Synthesis of titanium, zirconium, and hafnium complexes that contain diamido donor ligands of the type [(t-BuN-o-C6H4)2O]2- and an evaluation of activated versions for the polymerization of 1-hexene

Organometallics 1999, 18, 3649-3670

3649

Syn th esis of Tita n iu m , Zir con iu m , a n d Ha fn iu m

Com p lexes th a t Con ta in Dia m id o Don or Liga n d s of th e

Typ e [(t-Bu N-o-C₆H₄)₂O]^2-a n d a n Eva lu a tion of

Activa ted Ver sion s for th e P olym er iza tion of 1-Hexen e

Richard R. Schrock,* Robert Baumann, Steven M. Reid, J onathan T. Goodman,

Ru¨diger Stumpf, and William M. Davis

Department of Chemistry, Massachusetts Institute of Technology,

Cambridge, Massachusetts 02139

Received J une 29, 1999

Titanium, zirconium, and hafnium dialkyl complexes that contain the [(t-Bu-d₆-N-o-

C₆H₄)₂O]^2-([t-BuNON]^2-) ligand have been prepared. Only [t-BuNON]TiMe₂could be

isolated, but [t-BuNON]ZrR₂and [t-BuNON]HfR₂complexes could be isolated in which (for

example) R ) Me, Et, or i-Bu. X-ray studies showed [t-BuNON]MMe₂structures (M ) Ti or

Zr) to be of the “twisted fac” variety in which two amido nitrogens occupy equatorial positions

in a distorted trigonal bipyramid. However, in solution all such species show equivalent

alkyl groups on the NMR time scale as a consequence of formation of an intermediate mer

structure that contains a planar oxygen donor. In analogous complexes that contain the

{[Me(CD₃)₂CNC₆H₄][Me(CD₃)₂CN-2,4-Me₂C₆H₂]O}^2-or {[Me(CD₃)₂CNC₆H₄][Me(CD₃)₂N-2-

EtC₆H₃]O}^2-ligand the two metal alkyl groups are inequivalent on the NMR time scale.

Addition of trimethylphosphine to [t-BuNON]Zr(CH₂CH₃)₂yields structurally characterized,

pseudooctahedral [t-BuNON]Zr(η²-C₂H₄)(PMe₃)₂. Addition of B(C₆F₅)₃to [t-BuNON]ZrMe₂

yields structurally characterized {[t-BuNON]ZrMe}[MeB(C₆F₅)₃], while addition of [PhNMe₂H]-

[B(C₆F₅)₄] to [t-BuNON]ZrMe₂in bromobenzene-d₅generates “{[t-BuNON]ZrMe(PhNMe₂)]-

[B(C₆F₅)₄]”, which is an active catalyst for the polymerization of up to 500 equiv of 1-hexene

in a living manner at 0 °C. The analogous hafnium systems are not as well behaved, since

the dimethylaniline is insufficiently labile. No polymerization activity is observed for activated

titanium dialkyl complexes. Polymerization activity is quenched upon addition of THF or

dimethoxyethane to the cationic complexes. An X-ray structure of {[t-BuNON]ZrMe(THF)₂]-

[B(C₆F₅)₄] shows it to be a pseudooctahedral species in which the [t-BuNON]^2-ligand adopts

a “twisted mer” geometry, while the X-ray structure of {[t-BuNON]ZrMe(MeOCH₂CH₂OMe)]-

[B(C₆F₅)₄] was found to be of the “twisted fac” variety. In the case of hafnium, pseudoocta-

hedral cationic bis-THF or DME complexes can be isolated even when the anion is [B(C₆H₅)₄]^-;

like all complexes that contain THF or DME they are essentially inactive for polymerization

of 1-hexene.

In tr od u ction

of variations, in particular chiral metallocenes for con-

trolling tacticity,⁸anions (e.g., [B(C₆F₅)₄]^-)^16,17that are

relatively weakly associated with the metal cation,^14,18-22

alkylalumoxanes (e.g., MAO^23-25) as alkyl acceptors, and

catalysts that contain only one cyclopentadienyl ring.^26-28

For more than forty years^1-4group 4 metallocene

complexes have been targeted as catalysts for the

polymerization of ethylene or monosubstituted olefins.^5-8

The active species in such circumstances is now widely

regarded to be a metal cation.^9-16In the last fifteen

years research has focused largely on the development

(12) Bochmann, M.; Wilson, L. M.; Hursthouse, M. B.; Short, R. L.

Organometallics 1986, 6, 2556.

(13) Eshuis, J . J . W.; Tan, Y. Y.; Meetsma, A.; Teuben, J . H.;

Renkema, J .; Evens, G. G. Organometallics 1992, 11, 362.

(14) Hlatky, G. G.; Turner, H. W.; Eckman, R. R. J . Am. Chem. Soc.

1989, 111, 2728.

(15) Turner, H. W.; Hlatky, G. G. (Exxon) Eur. Pat. Appl., 1988.

(16) Yang, X.; Stern, C. L.; Marks, T. J . Organometallics 1991, 10,

840.

(17) Hlatky, G. G.; Upton, D. J .; Turner, H. W. (Exxon) U.S. Pat.

Appl., 1990.

(18) J ia, L.; Yang, X.; Stern, C. L.; Marks, T. J . Organometallics

1997, 16, 842.

(19) Canich, A. M.; Turner, H. W. (Exxon) World Pat. Application,

1992.

(20) Reed, C. A. Acc. Chem. Res. 1998, 31, 133.

(21) Strauss, S. H. Chem. Rev. 1993, 93, 927.

(22) Beck, W.; Sunkel, K. Chem. Rev. 1988, 88, 1405.

(23) Kaminsky, W.; Steiger, R. Polyhedron 1988, 7, 2375.

(1) Breslow, D. S.; Newburg, N. R. J . Am. Chem. Soc. 1957, 79, 5072.

(2) Natta, G.; Pino, P.; Mazzanti, G.; Giannini, U. J . Am. Chem. Soc.

1957, 79, 2975.

(3) Breslow, D. S.; Newburg, N. R. J . Am. Chem. Soc. 1959, 81, 81.

(4) Chien, J . C. W. J . Am. Chem. Soc. 1959, 81, 86.

(5) Sinclair, K. B.; Wilson, R. B. Chem. Ind. 1994, 857.

(6) Kaminsky, W.; Ardnt, M. Adv. Polym. Sci. 1997, 127, 144.

(7) Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 255.

(8) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.;

Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143.

(9) Dyachkovskii, F. S.; Shilova, A. K.; Shilov, A. E. J . Polym. Sci.

Part C 1967, 16, 2333.

(10) J ordan, R. F. Adv. Organomet. Chem. 1991, 32, 325.

(11) Bochmann, M.; Lancaster, S. J . J . Organomet. Chem. 1992, 431,

C1.

Publication on Web 08/12/1999

3650 Organometallics, Vol. 18, No. 18, 1999

Schrock et al.

Sch em e 1

Most recently group 4 metal catalysts that have no

cyclopentadienyl ring bound to the metal have been

actively sought.²⁹One of the most intriguing discoveries

was that titanium dialkyl complexes containing propyl-

ene-bridged aryl-substituted diamido ligands such as

[ArNCH₂CH₂CH₂NAr]^2-(Ar ) 2,6-R₂C₆H₃, R ) Me,

i-Pr) would promote the living polymerization of es-

sentially neat 1-hexene when activated by B(C₆F₅)₃, as

long as the concentration of 1-hexene remained high.^30,31

We had been exploring the chemistry of triamidoamine

complexes, largely of Mo or W,³²and considered the

possibility of increasing reactivity by employing related

diamido/donor ligands and in particular the possibility

of employing complexes containing such ligands for the

polymerization of olefins. That quest was successful, as

we reported in a preliminary fashion; zirconium cata-

lysts that contain the [(t-Bu-d₆-N-o-C₆H₄)₂O]^2-([t-

BuNON]^2-) ligand were shown to polymerize 1-hexene

in a living fashion, even after a given quantity of

1-hexene had been consumed.³³We have also reported

some ¹³C-labeling studies that support the proposal that

the polymerization is a living process and that the olefin

inserts into the metal-alkyl bond primarily (>95%) in

a 1,2-fashion.³⁴We now report the full version of the

synthesis and structure of [t-BuNON]^2-complexes of

Ti, Zr, and Hf, some polymerization chemistry employ-

ing Zr and Hf initiators, and X-ray structures of two

(catalytically inactive) Zr cations that contain the

[t-BuNON]^2-ligand.

Resu lts

Syn th esis of Liga n d s. 2,2′-Dinitrodiphenyl ether

was prepared by the known nucleophilic aromatic

substitution using 2-nitrophenol and 2-fluoronitroben-

zene (Scheme 1).³⁵A derivative that bears methyl

groups ortho and para to the phenol oxygen can be

synthesized in an analogous fashion in ∼80% yield

(Scheme 1; R₁) R₂) Me). However, larger substituents

ortho to the phenolic oxygen slow the nucleophilic

substitution. For example, 2-ethyl-2′,6-dinitrodiphenyl

ether (R₁) Et, R₂) H) can be prepared in only

moderate yield overall. All derivatives can be hydrogen-

ated in high yield employing Pd on C.³⁶The proton NMR

spectrum of H₂[t-BuNONEt] revealed that the ethyl’s

methylene protons are diastereotopic on the NMR time

scale as a consequence (we propose) of hindered rotation

of one phenyl ring past the other.

Schiff bases are formed quantitatively in a reaction

between the dianilines and acetone-d₆in the presence

of molecular sieves as the dehydrating reagent. The

condensation can be monitored conveniently by ¹H NMR

and is complete within 3-7 days. The Schiff bases can

be used without purification in a reaction with LiMe to

produce the tert-butyl-substituted anilines [Me(CD₃)₂-

CNHC₆H₄]₂O (H₂[t-BuNON]), [Me(CD₃)₂CNHC₆H₄]-

[Me(CD₃)₂CNH-2,4-Me₂C₆H₂]O (H₂[t-BuNONMe₂]), and

[Me(CD₃)₂CNHC₆H₄][Me(CD₃)₂NH-2-EtC₆H₃]O (H₂[t-

BuNONEt]. The first two compounds can be prepared

on a multigram scale and are isolated as pale orange

oils in ∼55% overall yield. This synthesis of tert-butyl-

substituted anilines is analogous to the synthesis of

monodentate tert-butyl anilines reported by Cummins

and co-workers.³⁷Similar reactions with acetone itself

produced only low yields of the tert-butyl-substituted

(24) Kaminsky, W.; Bark, A.; Steiger, R. J . Mol. Catal. 1992, 74,

109.

(25) Sinn, H.; Kaminsky, W. Adv. Organomet. Chem. 1980, 18, 99.

(26) Chen, Y.-X.; Marks, T. J . Organometallics 1997, 16, 3649.

(27) Shapiro, P. J .; Bunel, E.; Schaefer, W. P.; Bercaw, J . E.

Organometallics 1990, 9, 867.

(28) McKnight, A. L.; Waymouth, R. M. Chem. Rev. 1998, 98, 2587.

(29) For leading references see: (a) Martin, A.; Uhrhammer, R.;

Gardner, T. G.; J ordan, R. F.; Rogers, R. D. Organometallics 1998, 17,

382. (b) Bei, X. H.; Swenson, D. C.; J ordan, R. F. Organometallics 1997,

16, 3282. (c) Tjaden, E. B.; Swenson, D. C.; J ordan, R. F.; Petersen, J .

L. Organometallics 1995, 14, 371.

(30) Scollard, J . D.; McConville, D. H.; Payne, N. C.; Vittal, J . J .

Macromolecules 1996, 29, 5241.

(31) Scollard, J . D.; McConville, D. H. J . Am. Chem. Soc. 1996, 118,

10008.

(32) Schrock, R. R. Acc. Chem. Res. 1997, 30, 9.

(33) Baumann, R.; Davis, W. M.; Schrock, R. R. J . Am. Chem. Soc.

1997, 119, 3830.

(34) Baumann, R.; Schrock, R. R. J . Organomet. Chem. 1998, 557,

69.

(35) Wilshire, J . F. K. Aust. J . Chem. 1988, 41, 995.

(36) Randall, J . J .; Lewis, C. E.; Slagan, P. M. J . Org. Chem. 1962,

27, 4098.

(37) Laplaza, C. E.; Davis, W. M.; Cummins, C. C. Organometallics

1995, 14, 577.

Ti, Zr, and Hf Diamido Complexes

Organometallics, Vol. 18, No. 18, 1999 3651

Sch em e 2

coordination requirements. The Ti-C and Ti-N dis-

tances are in the expected range, but the Ti-O bond is

relatively long (Ti(1)-O ) 2.402(4) Å). The sum of the

angles about the oxygen atom (∼315.5°) suggests that

it is tetrahedral, while the sum of the angles around

the amido atoms suggests that they are planar, as

expected. The [t-BuNON]^2-ligand is twisted to a

significant degree, in part, we presume, to minimize the

steric interaction of the tert-butyl groups with the axial

methyl group, but also as a consequence of the rigidity

of the planar o-phenylene “arm” that connects O to N.

The “twisted fac” structure has C₁symmetry, with one

tert-butyl group (on N(2)) pointing “away” from C(1), and

the other (on N(1)) pointing “toward” C(1).

anilines. Successful synthesis of the d₆derivatives is

perhaps the consequence of a significant isotope effect

that enhances the rate of nucleophilic attack at the

imine carbon versus deprotonation of the imine. Proton

NMR spectra (500 MHz) of H₂[t-BuNON] show two

small upfield shoulders on the tert-butyl resonance that

amount to ∼0.5 H per tert-butyl group. These additional

resonances are ascribed to methyl protons in partially

deuterated methyl groups (CD₂H and CDH₂). Exchange

of D for H is believed to originate from base-catalyzed

scrambling of NH protons into CD₃groups, either in

acetone-d₆or at some stage during imine formation.

These shoulders are also observed in H₂[t-BuNONMe₂]

and H₂[t-BuNONEt], as well as all metal complexes

reported here that contain diamidoether ligands of this

type. The practical consequence is that integrations for

tert-butyl protons in a [t-BuNON]^2-ligand typically

amount to ∼7 instead of 6.

The fact that [t-BuNON]TiMe₂appears to have C₂or

C_2vsymmetry on the NMR time scale suggests that fac

forms are interconverting rapidly via a mer intermediate

form in which Ti, N(1), N(2), and O are in a plane (eq

1). Either there is a molecular plane coincident with the

Syn th esis of Tita n iu m Com p lexes. Addition of 2

equiv of LiBu to a solution of H₂[t-BuNON] in ether,

followed by Ti(NMe₂)₂Cl₂, yields orange crystalline

[t-BuNON]Ti(NMe₂)₂in ∼55% yield (Scheme 2). Proton

NMR spectra of [t-BuNON]Ti(NMe₂)₂reveal only one

singlet at ∼3.1 ppm for the dimethylamide groups. The

dichloride complex, [t-BuNON]TiCl₂, was prepared in

∼80% yield by treating [t-BuNON]Ti(NMe₂)₂with

Me₃SiCl over a period of several days at 110 °C.

[t-BuNON]TiCl₂is a purple-black solid that is moder-

ately soluble in toluene and ether. A dimeric formulation

for [t-BuNON]TiCl₂cannot be ruled out, since [t-

BuNON]ZrCl₂was shown to be a dimer in the solid state

(see below). Reaction of Li₂[t-BuNON] (generated in

situ) with TiCl₄(thf)₂led to [t-BuNON]TiCl₂in only low

and irreproducible yields. Addition of methylmagnesium

chloride to [t-BuNON]TiCl₂gave [t-BuNON]TiMe₂in

Ti/N(1)/N(2)/O plane (C_2vsymmetry), or the mer form

is also “twisted” with a C₂axis bisecting the C-Ti-C

angle (C₂symmetry). In an ideal C_2vmer form two

methyl groups in each tert-butyl group would lie on

either side of an adjacent phenyl ring, leaving the third

to point directly between the methyl groups on titanium.

The aryl protons in the backbone ortho to oxygen would

also point directly toward one another. Therefore a

“twisted mer” (C₂) form seems more likely and has been

observed in two molecules that we will discuss later in

this paper. We propose that steric interactions between

the tert-butyl groups and the TiMe₂groups lead to a

further twisting of the ligand, a rotation of the TiMe₂

unit in the OTiMe₂plane, and conversion of the twisted

mer to the more stable twisted fac form. We cannot tell

if the molecule actually “flips” on the NMR time scale

through a C_2vform having a planar oxygen donor, or

not, as formation of the twisted mer (C₂) form is

sufficient in order to equilibrate the methyl groups on

Ti. A variable-temperature ¹H NMR study of [t-BuNON]-

TiMe₂in toluene-d₈down to -80 °C revealed no

evidence for any inequivalence of the Ti methyl groups

on the NMR time scale.

1

good yield. The room-temperature H NMR spectra of

[t-BuNON]TiMe₂show one singlet for the titanium

methyl groups and one singlet for the tert-butyl groups.

Attempts to prepare [t-BuNON]TiR₂complexes in which

one or more â hydrogens are present in the alkyl ligand

(e.g., R ) Et or i-Bu) were unsuccessful; only apparent

decomposition took place upon addition of the Grignard

reagent to [t-BuNON]TiCl₂.

An X-ray study of [t-BuNON]TiMe₂(Tables 1 and 3;

Figure 1a,b) showed it to be a “twisted,” approximately

trigonal bipyramidal molecule with equatorial amido

groups, an axial oxygen donor, and an axial methyl

group (C(2)-Ti(1)-(O) ) 175.6(2) Å). We call this the

“twisted fac” form. It is characterized by an angle

between the N(1)-Ti-O and N(2)-Ti-O planes of

approximately 120° (here 121°) and O-Ti-N(1)-C(17)

and O-Ti-N(2)-C(27) dihedral angles of 136-137°.

The equatorial methyl group is bent down slightly from

the ideal equatorial position (C(1)-Ti(1)-C(2) ) 96.0(2)°),

while the two amide atoms are bent away from the axial

methyl group even further (114.6(2)° and 115.1(2)°), we

presume as a consequence of the [t-BuNON]^2-ligand’s

Syn th esis of Zir con iu m Com p lexes. Reactions

between Zr(NMe₂)₄and H₂[t-BuNON], H₂[t-BuNONMe₂],

or H₂[t-BuNONEt] proceed smoothly to give bisdi-

methylamido complexes (Scheme 3; “[NON]” refers to

any of the ligands employed in this work). Reactions

involving H₂[t-BuNONMe₂] and H₂[t-BuNONEt] re-

quired 100 °C to proceed readily as a consequence of

more significant steric problems. Reaction of the dilithio

[t-BuNON]^2-salt with ZrCl₄or ZrCl₄(thf)₂yielded only

a mixture of unidentified species. Upon treatment with

Me₃SiCl in ether or toluene, [t-BuNON]Zr(NMe₂)₂com-

plexes are converted in high yield into dichloride

3652 Organometallics, Vol. 18, No. 18, 1999

Schrock et al.

Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t for [t-Bu NON]TiMe₂, {[t-Bu NON]Zr Cl₂}₂, [t-Bu NON]Zr Me₂,

a n d [t-Bu NON]Zr (η²-C₂H₄)(P Me₃)₂

[t-BuNON]TiMe₂

{[t-BuNON]ZrCl₂}₂

[t-BuNON]ZrMe₂

[t-BuNON]Zr(η²-C₂H₄)L₂

crystals obtained from

ether/pentane

ether

toluene

ether

formula

fw

C

₂₂H₃₂N₂OTi

C₂₀H₂₆Cl₂N₂OZ

472.55

C_25.5H₃₆N₂OZr

477.78

C₂₈H₄₈N₂OP₂Zr

581.84

388.40

crystal size (mm)

crystal system

space group

a (Å)

b (Å)

c (Å)

0.34 × 0.34 × 0.20

monoclinic

P2₁/c

14.376(4)

9.160(4)

16.456(7)

90

102.04(3)

90

2119.4(14)

4

0.10 × 0.10 × 0.04

monoclinic

P2₁/c

10.109(3)

17.174(4)

12.132(4)

90

97.893(13)

90

2086.5(10)

4

0.32 × 0.18 × 0.03

triclinic

P1h

0.23 × 0.15 × 0.12

orthorhombic

Pbca

15.85260(10)

19.3138(3)

19.52380(10)

90

9.135(3)

12.244(4)

12.529(6)

118.55(3)

90.55(2)

91.67(2)

1230.0(7)

2

1.290

0.465

502

185(2)

R (deg)

â (deg)

90

γ (deg)

V (Å³)

5977.68(10)

8

1.293

0.497

2464

Z

density calcd (Mg/m³)

1.217

0.416

832

158(2)

1.504

0.794

968

183(2)

µ (mm^-1

F(000)

T (K)

)

183(2)

θ range (ω scans) (deg)

no. of reflns collected

no. of indep reflns

1.45-23.26

2.03-23.26

1.85-23.25

1.96-23.27

3857

8385

5113

22901

2632

2984

3467

4278

no. of data/restr/params

goodness-of-fit on F²

R1/wR2 [I > 2σ(I)]

R1/wR2 (all data)

2632/0/236

1.182

0.0682/0.1482

0.0886/0.1688

0.0113(13)

0.463/-0.369

2980/0/236

1.243

0.0446/0.0864

0.0567/0.0945

0.0013(3)

0.379/-0.396

3466/0/281

0.999

0.0445/0.1125

0.0595/0.1331

0.0009(14)

0.485/-0.503

4277/0/308

1.048

0.0296/0.0675

0.0340/0.0698

0.00075(11)

0.303/-0.285

extinction coeff

max/min peaks (e/Å³)

Ta ble 2. Cr ysta l Da ta a n d Str u ctu r e Refin em en t for {[t-Bu NON]Zr Me}[MeB(C₆F ₅)₃],

{[t-Bu NON]Zr Me(THF )₂}[B(C₆F ₅)₄], a n d {[t-Bu NON]Zr Me(DME)}[B(C₆F ₅)₄]

{[t-BuNON]ZrMe}[MeB(C₆F₅)₃]

{[t-BuNON]ZrMe(THF)₂}⁺

{[t-BuNON]ZrMe(DME)}⁺

crystals obtained from

formula

fw

pentane

C₄₀H₃₂BF₁₅N₂OZr

943.71

THF/pentane

C₅₃H₄₅BF₂₀N₂O₃Zr

1239.94

DME/pentane

C₄₉H₃₉BF₂₀N₂O₃Zr

1185.85

crystal size (mm)

crystal system

space group

a (Å)

b (Å)

c (Å)

0.33 × 0.29 × 0.22

triclinic

P1h

0.3 × 0.3 × 0.3

monoclinic

P2₁/c

12.5537(3)

12.1378(3)

34.1037(9)

90

98.470(1)

90

5139.7(2)

4

0.34 × 0.22 × 0.08

triclinic

P1h

11.747(5)

12.321(5)

16.829(8)

100.21(3)

98.22(3)

108.06(3)

2228(2)

2

1.407

0.341

948

153(2)

10.6023(3)

14.3701(5)

16.2272(4)

90.930(1)

99.707(1)

97.771(1)

2412.61(12)

2

R (deg)

â (deg)

γ (deg)

V (Å³)

Z

density calcd (Mg/m³)

1.602

0.333

2504

173(2)

1.632

0.351

1192

185(2)

µ (mm^-1

F(000)

T (K)

)

θ range (ω scans) (deg)

no. of reflns collected

no. of indep reflns

1.26-20.00

1.21-23.25

1.88-23.25

4425

20491

9796

3722

7365

6704

no. of data/restr/params

goodness-of-fit on F²

R1/wR2 [I > 2σ(I)]

R1/wR2 (all data)

3709/0/536

1.068

0.0890/0.1857

0.1077/0.2136

0.0006(4)

0.817/-0.535

7365/0/721

1.322

0.0665/0.1153

0.0791/0.1191

6704/0/685

1.441

0.0832/0.1463

0.1030/0.1551

extinction coeff

max/min peaks (e/Å³)

0.410/-0.414

0.612/-0.683

complexes.³⁸Even in the presence of excess Me₃SiCl the

sterically protected ligand amido nitrogen atoms are not

alkylated under the conditions employed. The reaction

between [t-BuNON]Zr(NMe₂)₂and methyl iodide^39,40

proceeds more slowly than that between [t-BuNON]Zr-

(NMe₂)₂and Me₃SiCl, although upon heating a mixture

of [t-BuNON]Zr(NMe₂)₂and excess methyl iodide in

toluene to ∼50 °C, [t-BuNON]ZrI₂is formed in high

yield within 2 days.

In proton NMR spectra of [t-BuNON]Zr(NMe₂)₂the

NMe₂groups appear as one sharp singlet, consistent

with C₂or C_2vsymmetry of the molecular core and

ligand backbone and free rotation about the Zr-N bond

in solution on the NMR time scale. In contrast, proton

NMR spectra of [t-BuNONMe₂]Zr(NMe₂)₂feature two

sharp singlets (at 3.15 and 2.82 ppm) for two NMe₂

ligands in which rotation about the Zr-N bond is still

rapid on the NMR time scale. No coalescence of the

NMe₂resonances was observed when a chlorobenzene-

(38) Diamond, G. M.; J ordan, R. F.; Petersen, J . L. Organometallics

1996, 15, 4045.

(39) J ohnson, A. R.; Davis, W. M.; Cummins, C. C. Organometallics

1996, 15, 3825.

(40) J ohnson, A. R.; Wanandi, P. W.; Cummins, C. C.; Davis, W. M.

Organometallics 1994, 13, 2907.

Ti, Zr, and Hf Diamido Complexes

Organometallics, Vol. 18, No. 18, 1999 3653

Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles (d eg) in [t-Bu NON]TiMe₂, {[t-Bu NON]Zr Cl₂}₂, a n d

[t-Bu NON]Zr Me₂

[t-BuNON]TiMe₂

{[t-BuNON]ZrCl₂}₂

[t-BuNON]ZrMe₂

Ti-O

2.402(4)

1.944(4)

1.936(4)

2.119(6)

2.097(6)

113.5(2)

73.9(2)

110.0(2)

115.1(2)

74.0(2)

105.7(2)

114.6(2)

175.6(2)

96.0(2)

80.2(2)

115.5(4)

128.0(3)

121

Zr-O

2.336(3)

2.089(4)

2.061(4)

2.4025(13)

2.5290(14)

101.88(14)

72.69(12)

98.79(12)

135.71(10)

73.28(12)

103.20(11)

135.71(10)

169.49(8)

110.89(5)

77.25(8)

115.5(3)

129.0(3)

135.3(3)

109

Zr-O

2.418(3)

2.096(4)

2.087(4)

2.280(5)

2.235(5)

113.19(14)

70.74(12)

113.6(2)

112.7(2)

71.16(12)

105.4(2)

111.8(2)

175.48(14)

99.2(2)

Ti-N(1)

Zr-N(1)

Zr-N(2)

Zr-N(1)

Zr-N(2)

Ti-N(2)^a

Ti-C(2)(ax)

Zr-Cl(2)(ax)

Zr-Cl(1)(eq)

N(1)-Zr-N(2)

N(1)-Zr-O

N(1)-Zr-Cl(2)

N(1)-Zr-Cl(1)

N(2)-Zr-O

N(2)-Zr-Cl(2)

N(2)-Zr-Cl(1)

Cl(2)-Zr-O

Cl(2)-Zr-Cl(1)

Cl(1)-Zr-O

C(1)-O-C(7)

Zr-N(1)-C(101)

Zr-N(2)-C(201)

N(1)/Zr/O/N(2)^b,c

O-Zr-N(1)-C(101)^c

O-Zr-N(2)-C(201)^c

Zr-Cl(1A)

Zr-C(2)(ax)

Zr-C(1)(eq)

N(1)-Zr-N(2)

N(1)-Zr-O

N(1)-Zr-C(2)

N(1)-Zr-C(1)

N(2)-Zr-O

N(2)-Zr-C(2)

N(2)-Zr-C(1)

C(2)-Zr-O

C(2)-Zr-C(1)

C(1)-Zr-O

C(11)-O-C(21)

Zr-N(1)-C(17)

Zr-N(2)-C(27)

N(1)/Zr/O/N(2)^b,c

O-Zr-N(1)-C(17)^c

O-Zr-N(2)-C(27)^c

Ti-C(1)(eq)

N(1)-Ti-N(2)

N(1)-Ti-O

N(1)-Ti-C(2)

N(1)-Ti-C(1)

N(2)-Ti-O

N(2)-Ti-C(2)

N(2)-Ti-C(1)

C(2)-Ti-O

C(2)-Ti-C(1)

C(1)-Ti-O

C(12)-Ti-C(26)

Ti-N(1)-C(17)

Ti-N(2)-C(27)

N(1)/Ti/O/N(2)^b,c

O-Ti-N(1)-C(17)^c

O-Ti-N(2)-C(27)^c

79.8(2)

117.2(3)

123.1(3)

126.6(3)

124

146.1

142.9

137.3

136.3

143.3

135.5

2.7944(13)

a

b

In all compounds the tert-butyl group on N(2) is turned toward the region between N(1) and N(2). The external angle between the

planes. ^cObtained from Chem 3D model.

Sch em e 3

on the NMR time scale. In this case the molecule must

pass through a true C_2vtransition state in order to

interconvert the two dimethylamido ligands; a “twisted

mer” transition state in which a C₂axis passes between

the two ZrMe₂methyl groups is insufficient. Proton

NMR spectra of [t-BuNONEt]Zr(NMe₂)₂at room tem-

perature also show two distinct NMe₂resonances.

The X-ray structure of [t-BuNON]ZrCl₂(Tables 1 and

3, Figure 2) shows it to be a dimer having a crystal-

lographic inversion center. Each zirconium has a dis-

torted trigonal bipyramidal coordination geometry simi-

lar to what is found in [t-BuNON]TiMe₂, with an axial

chloride (Zr-Cl(2) ) 2.4025(13)) and an equatorial

chloride (Zr-Cl(1) ) 2.5290(14)). A chloride that is in

an equatorial position with respect to the second zirco-

nium (Cl(1A)) is bonded to the N(2)-Cl(1)-Cl(2) face

at a distance of 2.7944(13) Å. (The N(2)-Cl(1)-Cl(2) face

is that from which the tert-butyl group turns away, i.e.,

C(201) points toward N(1), thereby providing room for

the weakly bound Cl(1A).) For comparison, in {Cl₂Zr-

F igu r e 1. (a) ORTEP diagram (35% probability level) of

[t-BuNON]TiMe₂. (b) Chem 3D view of [t-BuNON]TiMe₂]

from the axial position.

41

(NSiHMe₂)₂}₂the Zr-Cl_bridgebond lengths are 2.599

and 2.628 Å, respectively. The Zr-O bond length

d₅solution of [t-BuNONMe₂]Zr(NMe₂)₂was heated to

120 °C. We propose that the lowest energy form of

[t-BuNONMe₂]Zr(NMe₂)₂is a twisted fac structure and

that the phenyl groups cannot pass one another rapidly

(2.336(3) Å) is approximately what would be expected

(41) Herrmann, W. A.; Huber, N. W.; Behm, J . Chem. Ber. 1992,

125, 1405.

3654 Organometallics, Vol. 18, No. 18, 1999

Schrock et al.

The X-ray structure of [t-BuNON]ZrMe₂is shown in

Figure 3. (See also Tables 1 and 3.) The molecule is a

twisted fac form in the solid state, similar to [t-BuNON]-

TiMe₂. The equatorial positions are occupied by the two

ligand nitrogen atoms [N(1)-Zr-N(2) ) 113.19(14)°]

and one methyl group. The other methyl group (con-

taining C(2)) and the oxygen donor are in axial positions

[C(2)-Zr-O ) 175.48(14)°]. The sum of the angles about

oxygen is ∼329°. The only significant structural differ-

ences between [t-BuNON]ZrMe₂and [t-BuNON]TiMe₂

are the more normal Zr-O distance (Zr-O ) 2.418(3)

Å) and the slightly larger O-Zr-N-C dihedral angles.

Several dialkyl complexes in which the alkyl contains

one or more â hydrogens (R ) Et, n-Pr, i-Bu) also can

be isolated as highly pentane soluble, pale yellow solids

in ∼50% yield. At -25 °C all three can be stored in the

solid state for months or in ether solution for several

days without decomposition. However, at room temper-

ature in C₆D₆or ether solution they decompose within

several hours to a mixture of unidentified products.

When [t-BuNON]ZrCl₂is treated with 1 or 2 equiv of

Me₃CCH₂MgCl, [t-BuNON]Zr(CH₂CMe₃)Cl is obtained,

while addition of 2 equiv of LiCH₂CMe₃to [t-BuNON]-

ZrCl₂leads to a mixture of unidentified products.

Apparently a complex that contains two neopentyl

groups is too crowded to form, and some alternative

pathway leads to decomposition during its attempted

formation. We propose that the neopentyl group in

[t-BuNON]Zr(CH₂CMe₃)Cl is located in the sterically

more open equatorial position in a fac structure, while

the chloride occupies the more crowded axial position

trans to the oxygen donor.

F igu r e 2. ORTEP diagram (35% probability level) of {[t-

BuNON]ZrCl₂}₂.

for a Zr-O_donorbond, and the sum of the angles about

the oxygen atom (∼328.5°) suggests that it is tetrahe-

dral. The N(1)-Zr-N(2) angle and the angle between

the N(1)-Zr-O and N(2)-Zr-O planes is approxi-

mately 10° smaller than the corresponding angles in the

other (five-coordinate) species listed in Table 3, consist-

ent with a more crowded pseudo-six-coordinate coordi-

nation sphere in {[t-BuNON]ZrCl₂}₂, while the Zr-N

bond lengths (2.061(4) and 2.089(4) Å) are approxi-

mately 0.1 Å longer than the corresponding Ti-N bond

lengths, as one would expect. An ipso carbon atom in

one phenyl ring (C(8)) weakly interacts with the zirco-

nium metal center (Zr‚‚‚C(8) ) 2.774(4) Å), as also has

been observed in compounds such as [1,2-(NSi-i-

Pr₃)₂C₆H₄]₂Zr,⁴²where Zr-C_ipso≈ 2.60 Å. It is believed

to be a consequence of the [t-BuNON]^2-ligand’s con-

formation in a crowded environment, not a determinant

of that conformation. For convenience, and since a

dimeric formulation was confirmed for only one dichlo-

ride complex, all [NON]ZrX₂(X ) Cl or I) complexes

will be written as monomers in the text of this paper

with the understanding that they almost certainly are

dimers in the solid state.

When an ether solution of [t-BuNON]ZrEt₂is allowed

to stand at -25 °C in the presence of excess PMe₃,

[t-BuNON]Zr(η²-C₂H₄)(PMe₃)₂forms over a period of 2

days and can be isolated in ∼80% yield (eq 2). Since

Alkylation of [NON]ZrX₂precursors with methyl

Grignard reagents affords a variety of dimethyl com-

plexes in 50-75% yield (Scheme 3). [t-BuNONMe₂]-

ZrMe₂is highly soluble even in pentane and conse-

quently could be isolated in only ∼55% yield as a pale

yellow amorphous solid. Proton NMR spectra of [t-

BuNON]ZrMe₂are virtually identical to those of [t-

BuNON]TiMe₂. However, the zirconium methyl groups

in [t-BuNONMe₂]ZrMe₂are inequivalent and appear as

two distinct singlets. Heating a solution of [t-BuNONMe₂]-

ZrMe₂in toluene-d₈to 70 °C did not lead to significant

broadening of the zirconium methyl resonances. At

temperatures higher than ∼70 °C the sample decom-

posed to a mixture of unidentified species. The meth-

ylene protons of the ethyl group in [t-BuNONEt]ZrMe₂

give rise to two distinct doublets of triplets, as expected

since the phenyl rings of the ligand cannot pass one

another on the NMR time scale even in the free form of

the ligand. At temperatures up to 90 °C, where the

sample of [t-BuNONEt]ZrMe₂in toluene-d₈decomposed,

there was no evidence that the methylene protons could

interconvert on the NMR time scale.

[t-BuNON]ZrEt₂does not decompose at this tempera-

ture in the absence of PMe₃, the â hydrogen abstraction

reaction must be induced by coordination of PMe₃to Zr.

According to ¹H and ³¹P NMR studies, the PMe₃is

labile. A variable-temperature ³¹P NMR study in toluene-

d₈shows a broad signal at -29.9 ppm at 0 °C. At -40

°C this resonance is sharp. The thermal stability of

[t-BuNON]Zr(η²-C₂H₄)(PMe₃)₂in C₆D₆is moderate, but

is much higher in the presence of additional PMe₃,

suggesting that decomposition occurs via initial loss of

PMe₃. All attempts to isolate a monophosphine ethylene

derivative have failed. Attempts to isolate olefin com-

plexes analogous to [t-BuNON]Zr(η²-C₂H₄)(PMe₃)₂via

decomposition of [t-BuNON]ZrPr₂or [t-BuNON]Zr(i-

Bu)₂in the presence of PMe₃failed, perhaps because

the second phosphine is not firmly bound.

An X-ray structure of [t-BuNON]Zr(η²-C₂H₄)(PMe₃)₂

(Tables 1 and 5, Figure 4) shows that it is a pseudo-

octahedral species in which the [t-BuNON]^2-ligand is

bound in a twisted mer manner and the two PMe₃

(42) Aoyagi, K.; Gantzel, P. K.; Kalai, K.; Tilley, T. D. Organo-

metallics 1996, 15, 923.

Ti, Zr, and Hf Diamido Complexes

Organometallics, Vol. 18, No. 18, 1999 3655

(2.253(2) and 2.256(2) Å), on the other hand, are long

relative to what they are in zirconium complexes that

contain the fac form of the [t-BuNON]^2-ligand. The

Zr-P bond distances (2.8284(7) and 2.8100(7) Å) are

also longer than the Zr-P distance in Cp₂Zr(η²-CH₂-

CH₂)(PMe₃) (2.695(1) Å). It appears that while the

oxygen atom interacts strongly with the metal center,

both the Zr-P bonds and the π component of the Zr-N

bonds are weakened as a consequence of steric crowding

in the pseudo-six-coordinate geometry. The lability of

PMe₃in solution is consistent with the long Zr-P bond.

The electron count in [t-BuNON]Zr(η²-C₂H₄)(PMe₃)₂is

14 if the Zr-N π bond that utilizes the unsymmetric

combination of p orbitals on the nitrogen atoms is

included.

Syn th esis of Ha fn iu m Com p lexes. The most con-

venient entry into Hf chemistry is analogous to that

shown in Scheme 2 for zirconium complexes. The

reaction between H₂[t-BuNON] and Hf(NMe₂)₄in con-

centrated toluene solution at 100-105 °C for 16 h gave

[t-BuNON]Hf(NMe₂)₂in 82% yield. The purity of [t-

BuNON]Hf(NMe₂)₂was sufficiently high to use it with-

out further purification in a subsequent reaction with

Me₃SiCl. The dimethylamido methyl groups are equiva-

lent on the NMR time scale at room temperature in

[t-BuNON]Hf(NMe₂)₂(at 3.01 ppm), as they are in

[t-BuNON]Zr(NMe₂)₂and [t-BuNON]Ti(NMe₂)₂. The

reaction between [t-BuNON]Hf(NMe₂)₂and excess

Me₃SiCl in toluene at 100 °C for 5 h gave [t-BuNON]-

HfCl₂in 90% yield. [t-BuNON]HfCl₂can be used

without purification in subsequent alkylation reactions

in diethyl ether at -40 °C with the appropriate Grig-

nard reagent to give dialkyl derivatives [t-BuNON]HfR₂

(R ) Me, Et, i-Bu) in 70-80% isolated yields. As in the

case of [t-BuNON]ZrCl₂, only monoalkylation took place

upon addition of Me₃CCH₂MgCl to [t-BuNON]HfCl₂to

give [t-BuNON]Hf(CH₂CMe₃)Cl in 87% yield. Addition

of 2 equiv of neopentyllithium to [t-BuNON]HfCl₂gave

mixtures that appeared to contain crude [t-BuNON]Hf-

(CH₂CMe₃)₂(by ¹H NMR), but several attempts to

isolate [t-BuNON]Hf(CH₂CMe₃)₂in pure form were

unsuccessful. However, [t-BuNON]Hf(CH₂CMe₃)Me could

be prepared in good yield from the reaction between

[t-BuNON]Hf(CH₂CMe₃)Cl and MeMgI. NMR spectra

for the symmetric dialkyl derivatives show one set of

resonances for the alkyl ligands, suggesting that in

solution these complexes are interconverting rapidly

between fac and mer forms. [t-BuNON]HfEt₂and

[t-BuNON]Hf(CH₂CHMe₂)₂do not decompose at room

temperature in the solid state and at least for several

days in solution (C₆D₆, ether, or pentane) at room

temperature, in contrast to their less stable Zr ana-

logues.

F igu r e 3. ORTEP diagram (35% probability level) of

[t-BuNON]ZrMe₂.

F igu r e 4. ORTEP diagram (35% probability level) of

[t-BuNON]Zr(η²-C₂H₄)(PMe₃)₂.

ligands are trans to one another. The external angle

between the N(1)-Zr-O and N(2)-Zr-O planes is 177°

and the O-Zr-N-C_t-Budihedral angles are 159° and

165°, both significantly larger than in the twisted fac

structures. The ligand oxygen donor atom is essentially

planar, judging from the sum of the angles around it

(359°). The ethylene ligand is trans to the oxygen and

lies ∼15° out of the P-O-Zr-P plane. The Zr-CH₂

distances (Zr(1)-C(1A) ) 2.285(3) Å, Zr(1)-C(1B) )

2.288(3) Å) are slightly shorter than the zirconium to

ethylene carbon distances in Cp₂Zr(η²-CH₂CH₂)(PMe₃)

(Zr-C ) 2.354(3) and 2.332(4) Å),^43,44while the C(1A)-

C(1B) bond length (1.469(4) Å) is virtually identical to

that in Cp₂Zr(η²-CH₂CH₂)(PMe₃) (1.449(6) Å). The rela-

tively short Zr-O bond distance (2.295(2) Å) is consist-

ent with a strong interaction, while the Zr-N distances

Obser va tion a n d Isola tion of Ca tion s. When 1

equiv of B(C₆F₅)₃is added to a C₆D₅Br solution of

[t-BuNON]ZrMe₂, the color changes immediately to

bright yellow as {[t-BuNON]ZrMe}[MeB(C₆F₅)₃] is formed

(Scheme 4). The ¹H NMR spectrum of the solution shows

one sharp singlet at 0.77 ppm that we assign to the

equatorial ZrMe protons and a broad singlet at 2.24 ppm

that we assign to the Zr‚‚‚Me‚‚‚B protons. (The reso-

nance of the bridging methyl group is broadened due to

coupling to boron.) The tert-butyl groups are equivalent

on the NMR time scale and appear as a singlet at 0.98

(43) Binger, P.; Mu¨ller, P.; Benn, R.; Rufinska, A.; Gabor, B.; Kru¨ger,

C.; Betz, P. Chem. Ber. 1989, 122, 1035.

(44) Alt, H. G.; Denner, C. E.; Thewalt, U.; Rausch, M. D. J .

Organomet. Chem. 1988, 356, C83.

3656 Organometallics, Vol. 18, No. 18, 1999

Schrock et al.

Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles (d eg) in {[t-Bu NON]Zr Me}[MeB(C₆F ₅)₃],

{[t-Bu NON]Zr Me(THF )₂}[B(C₆F ₅)₄], a n d {[t-Bu NON]Zr Me(DME)}[B(C₆F ₅)₄]

{[t-BuNON]ZrMe}[MeB(C₆F₅)₃] {[t-BuNON]ZrMe(THF)₂}[B(C₆F₅)₄] {[t-BuNON]ZrMe(DME)}[B(C₆F₅)₄]

Zr-O

2.256(8)

2.049(10)

2.065(10)

2.487(12)^a

113.8(4)

73.5(4)

Zr-O(1)

2.302(3)

2.140(4)

2.160(4)

2.284(5)

137.20(15)

69.37(13)

68.72(13)

159.58(16)

99.33(17)

123.27(16)

125.2(4)

127.5(3)

118.9(3)

171

158.0(4)

175.6(4)

2.212(3)

96.90(14)

84.9814)

103.91(12)

173.48(12)

89.44(14)

91.44(14)

79.75(12)

Zr-O(1)

2.458(5)

2.061(5)

2.096(5)

2.238(7)

106.1(2)

71.58(19)

70.90(18)

171.1(2)

104.3(3)

103.5(3)

116.4(5)

131.5(4)

127.6(4)

115

132.2(6)

145.4(6)

2.259(5)

2.339(5)

130.2(2)

95.7(2)

Zr-N(1)

Zr-N(2)

Zr-C(1)

N(1)-Zr-N(2)

N(1)-Zr-O

N(2)-Zr-O

C(1)-Zr-O

N(1)-Zr-C(1)

N(2)-Zr-C(1)

C(11)-O-C(26)

Zr-N(1)-C(17)

Zr-N(2)-C(27)

N(1)/Zr/O/N(2)^b,c

O-Zr-N(1)-C(17)^c

O-Zr-N(2)-C(27)^c

Zr-C(2)

N(1)-Zr-C(2)

N(2)-Zr-C(2)

C(2)-Zr-O

C(2)-Zr-C(1)

B-C(1)

Zr-N(2)

Zr-C(1)

Zr-N(2)

Zr-C(1)

N(1)-Zr-N(2)

N(1)-Zr-O(1)

N(2)-Zr-O(1)

C(1)-Zr-O(1)

N(1)-Zr-C(1)

N(2)-Zr-C(1)

C(11)-O-C(12)

Zr-N(1)-C(2)

Zr-N(2)-C(18)

N(1)/Zr/O/N(2)^b,c

O-Zr-N(1)-C(2)

O-Zr-N(2)-C(18)

Zr-O(2)

N(1)-Zr-N(2)

N(1)-Zr-O(1)

N(2)-Zr-O(1)

C(1)-Zr-O(1)

N(1)-Zr-C(1)

N(2)-Zr-C(1)

C(11)-O-C(12)

Zr-N(1)-C(5)

Zr-N(2)-C(18)

N(1)/Zr/O/N(2)^b,c

O-Zr-N(1)-C(5)

O-Zr-N(2)-C(18)

Zr-O(2)

75.2(3)

167.3(4)

118.6(5)

101.2(5)

116.4(11)

125.8(7)

129.3(8)

121

140.3

125.4

2.200(13)

113.8(5)

115.4(5)

79.2(4)

Zr-O(3)

O(2)-Zr-N(1)

O(2)-Zr-N(2)

O(2)-Zr-O(1)

O(2)-Zr-O(3)

O(3)-Zr-N(1)

O(3)-Zr-N(2)

O(3)-Zr-O(1)

O(2)-Zr-N(1)

O(2)-Zr-N(2)

O(2)-Zr-O(1)

O(2)-Zr-O(3)

O(3)-Zr-N(1)

O(3)-Zr-N(2)

O(3)-Zr-O(1)

91.8(5)

1.69(2)

74.43(17)

67.89(17)

88.1(2)

163.2(2)

106.52(17)

a

b

Methyl group bridging between Zr and B. The external angle between the planes. ^cObtained from Chem 3D model.

Ta ble 5. Selected Bon d Dista n ces (Å) a n d An gles

(d eg) in [t-Bu NON]Zr (η²-CH₂CH₂)(P Me₃)₂

Distances

Zr-N(2)

Zr-C(1A)

Zr-P(1)

Zr-O

2.253(2)

2.285(3)

2.8284(7)

2.295(2)

Zr-N(1)

2.256(2)

2.288(3)

2.8100(7)

1.469(4)

Zr-C(1B)

Zr-P(2)

C(1A)-C(1B)

Angles

N(2)-Zr-N(1)

N(2)-Zr-O

137.94(7) C(1A)-Zr-C(1B)

37.48(10)

79.05(5)

83.65(5)

162.65(2)

124.8(2)

126.0(2)

128.1(2)

68.53(6) O-Zr-P(1)

N(2)-Zr-P(2)

N(2)-Zr-P(1)

N(1)-Zr-O

85.34(5) O-Zr-P(2)

89.57(5) P(2)-Zr-P(1)

69.50(7) C(6)-O-C(8)

87.37(5) C(31)-N(1)-Zr

85.33(5) C(41)-N(2)-Zr

N(1)-Zr-P(2)

N(1)-Zr-P(1)

N(1)/Zr/O/N(2)^a,b177

O-Zr-N(1)-C(31)^b165

O-Zr-N(2)-C(41)^b159

a

The external angle between the planes. ^bObtained from Chem

3D model.

Sch em e 4

F igu r e 5. ORTEP diagram (35% probability level) of {[t-

BuNON]ZrMe}[MeB(C₆F₅)₃].

multiplet) for the methyl group bridging between Zr and

B.

The reaction between [t-BuNON]ZrMe₂and B(C₆F₅)₃

also takes place in pentane. A solution of {[t-BuNON]-

ZrMe}[MeB(C₆F₅)₃] forms, from which at -35 °C a

yellow crystalline sample could be isolated in ∼46%

yield. This isolated sample contains 0.5 equiv of pen-

tane, according to ¹H NMR spectra. An X-ray structure

(Tables 2 and 4, Figure 5) reveals that the axial methyl

group has been partially abstracted from the zirconium

center. The Zr-C(1) bond length (2.487(12) Å) is length-

ened by ∼0.2 Å compared to what it is in [t-BuNON]-

ppm. Carbon NMR spectra show two different methyl

group resonances, one at 50.90 ppm for the methyl

group bound to Zr and another at 29.5 ppm (a broad

Ti, Zr, and Hf Diamido Complexes

Organometallics, Vol. 18, No. 18, 1999 3657

ZrMe₂. In related metallocene complexes^45,46Zr‚‚‚Me

bond distances are ∼2.549-2.667 Å. The Zr-ligand

bond lengths otherwise are contracted only slightly from

what they are in [t-BuNON]ZrMe₂, most noticeably in

the Zr-O bond length (2.256(8) Å), consistent with the

developing cationic charge on zirconium.

ether and C₆D₆gave “{[t-BuNON]ZrMe(ether)₂}-

[B(C₆F₅)₄]”; the ¹³C NMR spectrum consisted of a single

zirconium methyl resonance at 54.84 ppm. Multiple

attempts to obtain a crystalline product were unsuc-

cessful. The product was obtained as a solid in 92% yield

by addition of an ether solution of {[t-BuNON]ZrMe-

1

[t-BuNON]ZrMe₂reacts with 1 equiv of [PhNMe₂H]-

[B(C₆F₅)₄] in C₆D₅Br to give what we propose is {[t-

(ether)₂}[B(C₆F₅)₄] to cold pentane. The H NMR spec-

trum in C₆D₅Br contained a sharp resonance at 0.96

ppm for the zirconium methyl group and the tert-butyl

groups appeared as a single resonance at 1.46 ppm.

Dissolution of {[t-BuNON]ZrMe(ether)₂}[B(C₆F₅)₄] in

THF or DME yielded {[t-BuNON]ZrMe(THF)₂}[B(C₆F₅)₄]

and {[t-BuNON]ZrMe(DME)}[B(C₆F₅)₄], respectively.

(See below.)

1

BuNON]ZrMe(PhNMe₂)}[B(C₆F₅)₄] (Scheme 4). The H

NMR spectrum in C₆D₅Br shows a singlet for the

zirconium methyl group at 0.95 ppm. For comparison,

in C₆D₅Br the methyl groups of [t-BuNON]ZrMe₂ap-

pear at 0.66 ppm. At 25 °C the methyl resonances for

coordinated dimethyl aniline (at 2.74 ppm) and added

free dimethyl aniline (at 2.65 ppm) are broadened,

suggesting that dimethyl aniline is bound to Zr but

exchanging readily. Upon cooling this solution to -30

°C, the dimethylaniline methyl resonances sharpen. The

tert-butyl groups are equivalent. The ¹³C NMR spectrum

of {[t-BuNON]Zr(¹³CH₃)(PhNMe₂)}[B(C₆F₅)₄] showed a

single resonance for the zirconium methyl group at

55.88 ppm. Solutions of {[t-BuNON]ZrMe(PhNMe₂)}-

[B(C₆F₅)₄] in C₆D₅Br can be heated briefly to 50 °C,

although at that temperature decomposition is relatively

rapid. At room temperature {[t-BuNON]ZrMe(PhNMe₂)}-

[B(C₆F₅)₄] is stable for at least ∼1 h in solution.

Unfortunately, we have not yet been able to isolate a

solid sample of {[t-BuNON]ZrMe(PhNMe₂)}[B(C₆F₅)₄].

Solutions of {[t-BuNON]ZrMe(PhNMe₂)}[B(C₆F₅)₄] in

C₆H₅Cl or C₆D₅Br are bright yellow and homogeneous,

whereas dark orange oils separate out of toluene.

A methyl group also can be abstracted to give “{[t-

BuNON]ZrMe}[B(C₆F₅)₄]” by treating a C₆D₅Br solution

of [t-BuNON]ZrMe₂with [Ph₃C][B(C₆F₅)₄]; a sharp

singlet for Ph₃CMe appears at 2.01 ppm in the proton

NMR spectrum. The ¹H NMR resonances of {[t-BuNON]-

ZrMe}[B(C₆F₅)₄] are similar to those found for {[t-

BuNON]ZrMe(PhNMe₂)}[B(C₆F₅)₄]. In the absence of a

relatively good donor we propose that the metal is either

solvated by C₆D₅Br (by donation through bromide) or

forms a tight anion/cation pair. At room temperature

the zirconium methyl resonance in {[t-BuNON]ZrMe}-

[B(C₆F₅)₄] (at 0.72 ppm) is somewhat broader than in

{[t-BuNON]ZrMe(PhNMe₂)}[B(C₆F₅)₄], which suggests

that {[t-BuNON]ZrMe}[B(C₆F₅)₄] in C₆D₅Br may not be

as well-defined in terms of the nature of the interaction

between the cationic Zr center and the neutral base or

anion. The ¹³C NMR chemical shift of the methyl group

in {[t-BuNON]Zr(¹³CH₃)}[B(C₆F₅)₄] is 53.60 ppm (at 25

The THF adduct, {[t-BuNON]ZrMe(THF)₂}[B(C₆F₅)₄],

was prepared by adding 2 equiv of THF to a solution

of {[t-BuNON]ZrMe}[B(C₆F₅)₄] or {[t-BuNON]ZrMe-

(ether)₂}[B(C₆F₅)₄] in C₆H₅Cl; it was isolated in 72%

yield upon addition of pentane to the C₆H₅Cl solution.

1

The DME adduct could be prepared similarly. The H

NMR spectrum of {[t-BuNON]ZrMe(THF)₂}[B(C₆F₅)₄] in

C₆D₅Br contained a sharp single zirconium methyl

resonance at 1.03 ppm and three broadened resonances

at 3.9, 1.8, and 1.6 ppm that can be attributed to THF.

The ¹³C NMR spectrum of {[t-BuNON]Zr(¹³CH₃)(THF)₂}-

[B(C₆F₅)₄] revealed two broad methyl resonances at 53.4

and 55.6 ppm in a ratio of ∼10:1 that we ascribed to

isomers of the cation, perhaps fac and mer isomers

analogous to those observed in the Hf system (see

below). The ¹H NMR spectrum of {[t-BuNON]ZrMe-

(DME)}[B(C₆F₅)₄] contained a single zirconium methyl

resonance at 1.01 ppm. The resonances for the DME

appeared as two broadened resonances for methylene

protons at 3.62 and 3.86 ppm and a sharp singlet at

3.78 for the apparently equivalent methyl groups. The

¹³C NMR spectrum of {[t-BuNON]Zr(¹³CH₃)(DME)}-

[B(C₆F₅)₄] consisted of a single resonance at 52.47 ppm,

consistent with formation of only one isomer.

Crystals of {[t-BuNON]ZrMe(THF)₂}[B(C₆F₅)₄] suit-

able for single-crystal X-ray diffraction were obtained

from mixtures of THF and pentane (Tables 2 and 4,

Figure 6). The Zr atom is in a pseudooctahedral envi-

ronment with the [t-BuNON]^2-ligand in a twisted mer

conformation. The twisted mer conformation is sug-

gested by the large angle between the N(1)-Zr-O(1)

and N(2)-Zr-O(2) planes (171°) and O(1)-Zr-N-C_t-Bu

dihedral angles of 158° and 176°. These angles are

comparable to what are found for the twisted mer ligand

in [t-BuNON]Zr(η²-C₂H₄)(PMe₃)₂(Table 5). The ligand

oxygen donor atom (O(1)) is essentially planar, judging

from the sum of the angles around it (359°), as found

also in [t-BuNON]Zr(η²-C₂H₄)(PMe₃)₂. The CH₃group

occupies the position approximately trans to the ligand’s

oxygen donor (C(1)-Zr-O(1) ) 159.58(16)°), and the

THF donors are mutually trans. The Zr-ligand bonds

are all somewhat longer than they are in {[t-BuNON]-

ZrMe}[MeB(C₆F₅)₃], as would be expected in a com-

pound with a higher coordination number.

34

°C), compared to 45.2 ppm in [t-BuNON]Zr(¹³CH₃)₂

and 50.90 ppm for the terminal methyl group in the

incipient cation in {[t-BuNON]ZrMe}[MeB(C₆F₅)₃]. At

-30 °C the zirconium methyl group appears as three

broad resonances at 53.06, 50.16, and 44.20 ppm,

possibly as a consequence of a variety of anion and/or

solvent interactions with the cation that have compa-

rable stability. This phenomenon is still under investi-

gation in a variety of cations that contain diamido/donor

ligands.

Crystals of {[t-BuNON]ZrMe(DME)}[B(C₆F₅)₄] suit-

able for single-crystal X-ray diffraction were obtained

from mixtures of DME and pentane (Tables 2 and 4,

Figure 7). The Zr atom is in a pseudooctahedral envi-

ronment with the [t-BuNON]^2-ligand in a twisted fac

conformation. The twisted fac conformation is charac-

Abstraction of a methyl group from [t-BuNON]Zr-

(¹³CH₃)₂with [Ph₃C][B(C₆F₅)₄] in a 1:1 mixture of diethyl

(45) Bochmann, M.; Lancaster, S. J .; Hursthouse, M. B.; Malik, K.

M. A. Organometallics 1994, 13, 2235.

(46) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994,

116, 10015.

3658 Organometallics, Vol. 18, No. 18, 1999

Schrock et al.

{[t-BuNON]ZrMe(DME)}⁺from octahedral geometry

and its strong similarity with the distorted core in {[t-

BuNON]ZrCl₂}₂(Figure 2). In {[t-BuNON]ZrCl₂}₂Cl(1)

is in a position with respect to Zr(A) (and Cl(1A) with

respect to Zr in Figure 2) that is analogous to the

position of O(3) in {[t-BuNON]ZrMe(DME)}⁺; both

coordinate to the face on a five-coordinate core that is

more “open” as a consequence of the tert-butyl group

on the amido nitrogen (N(1) in {[t-BuNON]ZrMe-

(DME)}⁺) turning toward the other amido ligand, i.e.,

being twisted in a clockwise direction in the view in

Figure 7. (In Figure 2 the twist at Zr(A) is clockwise;

the twist at the other Zr center is counterclockwise.) The

chloride and oxygen that are bound to this more open

face in less than an ideal position have the longer Zr-

ligand bond lengths, e.g., Zr-O(2) ) 2.259(5) Å, while

Zr-O(3) ) 2.339(5) Å. On the NMR time scale at room

temperature we believe that {[t-BuNON]ZrMe(DME)}⁺

is oscillating from one twisted fac form to the other,

thereby yielding equivalent DME methyl (proton or

carbon) resonances but still inequivalent methylene

proton resonances (“up” and “down”).

F igu r e 6. ORTEP drawing (50% probability level) of the

structure of {[t-BuNON]Zr(CH₃)(THF)₂}⁺. (Anion not

shown.)

Addition of 1 equiv of [PhNMe₂H][B(C₆F₅)₄] to a C₆D₅-

Br solution of [t-BuNON]HfMe₂at 22 °C produced {[t-

BuNON]HfMe(PhNMe₂)}[B(C₆F₅)₄] in high yield, ac-

1

cording to NMR spectra. The H NMR spectrum of {[t-

BuNON]HfMe(PhNMe₂)}[B(C₆F₅)₄] in C₆D₅Br shows a

methyl resonance at 0.89 ppm, a singlet at 2.79 ppm

for bound Me₂NPh, and a resonance at 2.66 ppm for a

trace of free Me₂NPh. The ¹³C{¹H} NMR spectrum of

{[t-BuNON]Hf(¹³CH₃)(PhNMe₂)}[B(C₆F₅)₄] contains a

methyl resonance at 64.90 ppm (cf. 56.32 ppm in

[t-BuNON]HfMe₂). Addition of approximately 1 equiv

of free dimethylaniline yields a resonance at 2.66 ppm

for the methyl group in free aniline. These data suggest

that exchange of coordinated and free aniline is slow

on the NMR time scale at room temperature. When this

sample is heated, the methyl resonances for bound and

free dimethylaniline broaden and coalesce between 70

and 80 °C. No significant decomposition was observed,

even when the sample was held at 80 °C for 10-15 min,

and the original spectrum was regenerated when the

sample was cooled back to room temperature. The

analogous Zr compound will not survive this treatment,

as noted earlier.

F igu r e 7. ORTEP drawing (50% probability level) of the

structure of {[t-BuNON]Zr(CH₃)(DME)}⁺. (Anion not shown.)

Protonation of [t-BuNON]HfMe₂with 1 equiv of

[PhNMe₂H][B(C₆F₅)₄] in C₆D₅Br at -40 °C led to the

rapid dissolution of the sparingly soluble ammonium

reagent, but there was no obvious evolution of methane,

as there is in a similar reaction performed at 22 °C. A

proton NMR spectrum at -35 °C suggested that two

methyl groups were still present in a complex that lacks

a plane of symmetry. We propose that one amido

nitrogen has been protonated and the unsymmetric

dimethyl complex shown in eq 3 has been formed.

terized by an angle between the N(1)-Zr-O(1) and

N(2)-Zr-O(2) planes of close to 115° and O(1)-Zr-N-

C_t-Budihedral angles similar to those found in {[t-

BuNON]ZrMe}[MeB(C₆F₅)₃] (132° and 145°) and [t-

BuNON]ZrMe₂(143° and 146°). The CH₃group is trans

to the [t-BuNON]^2-ligand’s oxygen donor (O(1)-Zr-

C(1) ) 171.1(2)°), with the DME coordinated to the Zr

atom in the two positions approximately trans to the

amido nitrogen donors with Zr-O bond distances of

2.259(5) (to O(2)) and 2.339(5) Å (to O(3)). The Zr-O(1)

bond length (2.458(5) Å) is the longest of the Zr-O_NON

bond lengths in the three complexes in Table 4, which

we assume to be a consequence of the six-coordinate

geometry combined with the greater degree of confor-

mational strain associated with the twisted fac ligand

relative to a twisted mer ligand. It is interesting to note

the significant distortion of the six-coordinate core in

Important spectral features for {[t-BuNHC₆H₄OC₆H₄N-

Ti, Zr, and Hf Diamido Complexes

Organometallics, Vol. 18, No. 18, 1999 3659

1

F igu r e 8. 500 MHz H NMR spectrum of {[t-BuNHC₆H₄OC₆H₄N-t-Bu]HfEt₂}⁺in CD₂Cl₂at 22 °C. *Resonances for what

is proposed to be [t-BuNON]HfCl(Et)(Me₂NPh).

t-Bu]HfMe₂}⁺include two equally intense tert-butyl

resonances at 1.06 and 1.03 ppm and two hafnium

methyl resonances at 0.55 and 0.53 ppm. A slightly

broadened singlet at 4.33 ppm with a relative intensity

of 1 was assigned to the N-H proton. The solution also

contained free Me₂NPh, according to the chemical shift

of the Me₂NPh protons (2.53 ppm at -35 °C). Over the

course of several minutes, resonances for {[t-BuNON]-

HfMe(PhNMe₂)}⁺and methane increased in intensity

as those for {[t-BuNHC₆H₄OC₆H₄N-t-Bu]HfMe₂}⁺gradu-

ally disappeared. The generation of {[t-BuNHC₆H₄-

OC₆H₄N-t-Bu]HfMe₂}⁺was always accompanied by the

formation of substantial amounts of {[t-BuNON]HfMe-

(PhNMe₂)}⁺, even when the reaction was performed at

-40 °C. The details of how {[t-BuNON]HfMe(PhN-

Me₂)}⁺forms from {[t-BuNHC₆H₄OC₆H₄N-t-Bu]HfMe₂}⁺

are not known.

Progressively more stable “N-H” species resulted

from protonation of [t-BuNON]HfEt₂or [t-BuNON]Hf-

(i-Bu)₂by [PhNMe₂H][B(C₆F₅)₄] in cold CD₂Cl₂. At 22

°C {[t-BuNHC₆H₄OC₆H₄N-t-Bu]HfEt₂}⁺persists for

hours. The ¹H NMR spectrum of {[t-BuNHC₆H₄OC₆H₄N-

t-Bu]HfEt₂}⁺(Figure 8) includes a singlet at 4.64 ppm

arising from the N-H moiety and two sets of tert-butyl

and ethyl resonances. The R-protons on the ethyl ligands

are diastereotopic, as indicated by two complex multi-

plets at 0.87 and 1.23 ppm, as should be the case for

with formation of an unsymmetric species of the type

shown in eq 3. The two isobutyl methyne multiplets are

well-separated at 2.41 and 1.52 ppm. Slow decomposi-

tion of {[t-BuNHC₆H₄OC₆H₄N-t-Bu]Hf(CH₂CHMe₂)₂}⁺

in CD₂Cl₂over the course of 1 day yielded isobutane

and resonances consistent with formation of a monoiso-

butyl chloride complex.

Several base-stabilized methyl cations could be pre-

pared by oxidation of [t-BuNON]HfMe₂with [Cp′₂Fe]-

BPh₄(Cp′ ) η⁵-C₅H₄Me) in the presence of oxygen

donors (THF or 1,2-dimethoxyethane) in toluene. {[t-

BuNON]HfMe(THF)₂}BPh₄was obtained in 62% yield

as colorless crystals. Proton and carbon NMR spectra

in CD₂Cl₂showed that it is approximately an equimolar

mixture of bis-THF adducts, one that has two planes of

symmetry (believed to be the mer isomer) and one that

has one plane of symmetry (believed to be the fac

isomer) with structures that are analogous to those of

mer-{[t-BuNON]ZrMe(THF)₂}⁺and fac-{[t-BuNON]-

ZrMe(DME)}⁺, respectively, described above. The meth-

yl resonance in the mer isomer is found at 0.72 ppm

and in the fac isomer at 0.55 ppm. Lowering the

temperature to -40 °C did not change the relative

intensities of each set of resonances, but in C₆D₅Br the

mer/ fac ratio was found to be 2.4. The fac resonances

could be assigned on the basis of the location of the tert-

butyl and methyl resonances in the related DME

complex, {[t-BuNON]HfMe(DME)}BPh₄, in which the

Hf-CH₃resonance is found at 0.51 ppm. Addition of a

slight excess of DME to a dichloromethane solution of

{[t-BuNON]HfMe(THF)₂}BPh₄at 22 °C resulted in the

quantitative formation of {[t-BuNON]HfMe(DME)}-

BPh₄, while dissolution of {[t-BuNON]HfMe(DME)}-

BPh₄in THF and cooling to -40 °C gave back crystalline

{[t-BuNON]HfMe(THF)₂}BPh₄. Addition of THF or

DME to {[t-BuNON]HfMe(PhNMe₂)}[B(C₆F₅)₄] in C₆D₅-

Br generated spectra for the THF and DME adducts,

the unsymmetric species shown in eq 3. Ethane (δ_H

)

0.85 ppm) was liberated gradually and free Me₂NPh

consumed over the course of several hours as resonances

appear for what we propose to be a monochloride

complex [t-BuNON]HfCl(Et)(PhNMe₂), formally the prod-

uct of chloride abstraction by putative {[t-BuNON]HfEt-

(PhNMe₂)}⁺.

1

The H NMR spectrum of {[t-BuNHC₆H₄OC₆H₄N-t-

Bu]Hf(CH₂CHMe₂)₂}⁺in CD₂Cl₂at 22 °C showed the

N-H resonance at 4.89 ppm and resonances consistent

3660 Organometallics, Vol. 18, No. 18, 1999

Schrock et al.

Ta ble 6. Da ta for P oly(1-h exen e) P r ep a r ed a t 0 °C

in Ch lor oben zen e Em p loyin g

of {[t-BuNON]ZrMe}[B(C₆F₅)₄] and other initiators for

1-hexene and the polymerization of other monomers will

be reported in due course elsewhere.

{[t-Bu -NON]Zr Me(P h NMe₂)}[B(C₆F ₅)₄] a s th e

In itia tor ^a

Labeling experiments suggest that an initiator pre-

pared from [t-BuNON]Zr(¹³CH₃)₂and [Ph₃C][B(C₆F₅)₄]

in bromobenzene-d₅will polymerize 1-hexene or 1-non-

ene by a 1,2-insertion process and that living poly(1-

hexene) decomposes at ∼40 °C in 10 min to yield largely,

but not exclusively, the product expected by â hydride

elimination.³⁴These results were confirmed here. The

poly(1-hexene) had a ¹³C NMR spectrum essentially

identical to that reported by McConville.³⁰In C₆D₅Br

the six resonances are found at 41.1 (br), 35.2 (br m),

33.2 (br s), 29.4 (m), 24.2 (∼s), and 15.2 (s) ppm; note

that the region between 24.2 and 15.2 contains no

resonances. The last two resonances were assigned to

C₅and C₆(the methyl group at the end of the side

chain), respectively, where the numbers correspond to

those in the 1-hexene monomer. The addition of 1 equiv

of 1-hexene to {[t-BuNON]Zr(¹³CH₃)}[B(C₆F₅)₄] yielded

a solution whose ¹³C NMR spectrum consisted primarily

of several resonances near ∼20 ppm, where one would

expect the resonance for a methyl adjacent to a methyne

carbon to be found, in addition to resonances near 30.8

and 24.0 ppm that have been assigned to the first and

second 1,2-insertion products, respectively.³⁴Addition

of 5 equiv of 1-hexene to a rapidly stirred solution of

activated [t-BuNON]Zr(¹³CH₃)₂resulted in the complete

consumption of the zirconium methyl cation, which

suggests that k_p/k_iis on the order of 5 or less.⁴⁷The

chemical shift for a ¹³CH₃group bound next to a

methylene carbon, which would be the result of a initial

2,1-addition process, would be expected to fall in the

area between 10 and 15 ppm.³⁴Upon the addition of 5

equiv of 1-hexene to the zirconium methyl cation, a

resonance at ∼15 ppm is observed, but this resonance

is due to natural abundant ¹³C in the methyl group in

the side chain of poly(1-hexene) (see above) and has an

intensity of ∼5% that of the resonances at 20 ppm for

the labeled methyl group from the initiator, as expected.

The low intensity of any resonance arising from the ¹³C

label in the initial methyl group at a position other than

∼20 ppm leads us to conclude that the percentage of

1,2-insertion in the first step of the polymerization

reaction is greater than at least 95%.

1-hexene

(equiv)

initiator

(µmol)

entry

M_n(calcd) M_n(found) M_w/M_n

1

2

3

4

5

6

7

8

9

49

179

229

288

343

399

408

517

49

45

52

50

47

52

55

4144

15027

19306

24262

28902

33593

34349

43481

103500

131700

137700

4877

14890

19520

24780

24590

35820

28030

39310

102500

97550

124900

1.14

1.08

1.04

1.02

1.05

1.04

1.03

1.11

1.20

1.11

46

1230

1565

1635

45^b

10

11

46 (3.5 h)

44^b

a

The initiator was prepared in situ and the reaction time was

1 h, unless noted otherwise; see Experimental Section for full

details. Polymer yields in each case were essentially quantitative.

b

For 10 h at -10 °C.

respectively, that were identical to the spectra for the

isolated BPh₄^-salts, consistent with no coordination or

-

reaction of BPh₄with the metal in the BPh₄salts.

All attempts to observe a titanium cation in chloro-

benzene or bromobenzene prepared by treating [t-

BuNON]TiMe₂with [Ph₃C][B(C₆F₅)₄] or [PhNMe₂H]-

[B(C₆F₅)₄] failed. The appearance of the sample was

consistent with decomposition to dark oily materials

that could not be identified.

P olym er iza tion of 1-Hexen e. We employ the poly-

merization of 1-hexene as a means of evaluating cata-

lysts for controlled polymerizations, primarily because

1-hexene can be handled easily and because poly(1-

hexene) is soluble and easy to characterize by gel

permeation chromatography at room temperature. Re-

actions involving zirconium initiators were run in a

batch mode in chlorobenzene at 0 °C with a known

amount of initiator and activator, unless otherwise

noted. (Polymerization reactions were run at 0 °C in

order to avoid a rise in temperature above 30 °C and

irreversible decomposition of the catalyst.³⁴) Data are

shown in Table 6 for the polymerization of 1-hexene by

{[t-BuNON]ZrMe(PhNMe₂)}[B(C₆F₅)₄]. The yield of poly-

(1-hexene) in all cases was quantitative.

The poly(1-hexene) has a narrow molecular weight

distribution, consistent with a single polymerization site

and little or no chain termination or transfer during the

course of the polymerization reaction. The number

average molecular weights (M_n(found), measured by

light scattering) are in good agreement with the ex-

pected values (M_n(calcd)). The measured molecular

weights appear to deviate from the expected values at

higher monomer loadings, although the inherent errors

in measuring the molecular weight of poly(1-hexene) are

large as a consequence of the small change in refractive

index with concentration (dn/dc). (See Experimental

Section.) Polymers with the expected molecular weights

in excess of 100 000 can be formed at -10 °C. Prepara-

tion of higher molecular weight polymers is impractical

using simple stirring techniques, as the reaction mix-

tures become too viscous.

Analogous experiments with {[t-BuNON]HfMe-

(PhNMe₂)}[B(C₆F₅)₄] as an initiator in C₆D₅Br at 22 °C

also yielded poly(1-hexene) (Table 7). As indicated by

entries 2 and 5, polymers prepared near room temper-

ature had molecular weights 2 to 3 times greater than

expected for a well-behaved living polymerization in

which k_pis on the same order as k_i. The molecular

weights were approximately those expected when poly-

merizations were performed at 50 °C if no more than

150 equiv of 1-hexene was employed (entries 1, 3, and

4), but M_n(found) dropped below M_n(calcd) in attempts

to prepare longer polymers (entries 6 and 7). GPC traces

of the polymers revealed unimodal distributions of

molecular weights and relatively low polydispersities.

No poly(1-hexene) was isolated in polymerizations at 22

°C to which additional Me₂NPh (3 equiv) had been

added, consistent with tight binding of PhNMe₂to Hf

1-Hexene is also polymerized by {[t-BuNON]ZrMe}-

[B(C₆F₅)₄] (prepared using the trityl method) in chlo-

robenzene at 0 °C, although characterization of such

polymers is not yet complete. Results concerning the use

(47) Gold, L. J . Chem. Phys. 1958, 28, 91.

Ti, Zr, and Hf Diamido Complexes

Organometallics, Vol. 18, No. 18, 1999 3661

Ta ble 7. Da ta for P oly(1-h exen e) P r ep a r ed a t 0 °C

in Ch lor oben zen e Em p loyin g

initiator and more intense resonances arising from poly-

(1-hexene). Therefore it appears that the rate of propa-

gation is significantly greater than the rate of initiation,

if we assume that 1-hexene mixes completely with the

initiator before much is polymerized. Resonances that

could be assigned to the first and second insertion

products, which was possible in the Zr system,³⁴were

not observed, consistent with a much larger ratio of k_p

to k_iin the Hf system than in the Zr system. Unfortu-

nately, detailed kinetic investigations that might yield

definitive values for k_pand k_iwere prevented by the

fact that unreacted initiator persisted even after the

consumption of 200 equiv of 1-hexene, at which point

solutions were prohibitively viscous for NMR analyses.

One possible explanation of the observed results is that

dimethylaniline is much more strongly bound in the

initiator (which has the smallest alkyl group) than in

the propagating species.

{[t-Bu -NON]HfMe(P h NMe₂)}[B(C₆F ₅)₄] a s th e

In itia tor ^a

1-hexene time^btemp

entry

(equiv)

(min) (°C) M_n(calcd) M_n(found) PDI

1

2

3

4

5

6

7

50

100

150

200

250

400

72

100

93

64

95

50

21

50

22

50

4208

8416

7900

24600

14300

10200

35000

13000

10600

1.53

1.20

1.74

1.49

1.19

1.33

1.30

12624

16832

21040

33664

58

465

a

The initiator was prepared in situ and the reaction time was

1 h, unless noted otherwise; see Experimental Section for full

details. Polymer yields in each case were essentially quantitative.

b

Time was that required for complete consumption of 1-hexene.

In view of the failure to observe a titanium cation in

chlorobenzene or bromobenzene upon treating [t-BuNON]-

TiMe₂with [Ph₃C][B(C₆F₅)₄] or [PhNMe₂H][B(C₆F₅)₄],

we were not surprised to find that all attempts to

polymerize 1-hexene in a well-behaved fashion using

activated [t-BuNON]TiMe₂failed. We also found that

none of the zirconium or hafnium cations that contained

an external oxygen donor (diethyl ether, THF, DME)

was active for the polymerization of 1-hexene and that

addition of diethyl ether, THF, or DME to any active

system led to an immediate loss of activity. (The ether

complex, {[t-BuNON]ZrMe(ether)₂}[B(C₆F₅)₄], yielded

traces of poly(1-hexene) after 18 h at 60 °C.) Polymer-

ization of 1-hexene by “{[t-BuNON]ZrMe(2,4-lutidine)}-

[B(C₆F₅)₄]” (prepared by adding 1 equiv of 2,4-lutidine

to {[t-BuNON]ZrMe(PhNMe₂)}[B(C₆F₅)₄]) at 0 °C also

failed.

F igu r e 9. Plot of M_n(b) and PDI (O) for poly(1-hexene)

prepared at temperature T with Hf catalyst. (See Experi-

mental Section for experimental details.)

(relative to Zr) and required loss of PhNMe₂in order

for an olefin to access the metal.

Averaged values for M_n(found) and PDI for poly(1-

hexene) (two runs each) prepared from 100 equiv of

1-hexene at 10 °C intervals between 40 and 80 °C are

shown in Figure 9. In each case the yields of poly(1-

hexene) were essentially quantitative. The expected

value for M_nis 8416 for a well-behaved living poly-

merization in which k_pis on the same order as k_i. It is

clear that at 40 °C M_n(found) is much greater than

M_n(calcd), approaches the expected value at tempera-

tures between 50 and 60 °C, and then continues to

decrease as the temperature is increased, while the

relatively low values for PDI at 40 °C increase to almost

2 at 80 °C. The inherent inaccuracy of determining the

M_nfor poly(1-hexene) does not allow us to conclude with

confidence that M_nactually decreases below the ex-

pected value of ∼8400, although that seems to be the

trend.

The complete consumption of 2 equiv of 1-hexene by

{[t-BuNON]Hf(¹³CH₃)(PhNMe₂)}[B(C₆F₅)₄] in C₆D₅Br at

22 °C was confirmed by ¹H NMR spectroscopy. The

¹³C{¹H} NMR spectrum of the resulting solution showed

that it contained a large amount of unreacted initiator

(δCH₃) 64.91). Several closely spaced resonances

centered near 20 ppm were assigned to the terminal

¹³CH₃end groups next to a methyne carbon, analogous

to what is observed in zirconium experiments described

above, which suggests that 1-hexene inserts into the

Hf(¹³CH₃) bond primarily in a 1,2 manner. The ¹³C{¹H}

NMR spectra in experiments described here show no

resonances between 10 and 15 ppm when only 1 equiv

of 1-hexene was employed. After addition of 20 more

equivalents of 1-hexene to the same sample, the ¹³C{¹H}

NMR spectrum still showed the presence of unreacted

Discu ssion

It has been known for some time that titanium alkyl

complexes that contain amido ligands are more stable

than simple chlorides.^48-51Even (R′₂N)₃TiR complexes

in which R contains one or more â protons (e.g., Et, Pr,

i-Pr) were found to be stable at temperatures up to 0

°C, which at the time was an unusually high stability

for titanium alkyl species containing a â proton.^48,52The

extensive work of Bu¨rger revealed that decomposition

of dialkylamido titanium complexes often involved an

N-C bond cleavage⁴⁹or abstraction of a proton R to

nitrogen.⁵³Bu¨rger also noticed that trimethylsilyl-

substituted amido complexes were much more stable

than dialkylamido complexes,⁵⁴a fact that he attributed

to the lower basicity of nitrogen atoms that have a silyl

substituent. Andersen prepared a variety of diamido

group 4 metal dialkyl complexes,^55,56especially those in

(48) De Vries, H. Recl. Trav. Chim. Pays-Bas 1961, 30, 866.

(49) Bu¨rger, H.; Neese, H.-J . J . Organomet. Chem. 1970, 21, 381.

(50) Bottrill, M.; Gavens, P. D.; Kelland, J . W.; McMeeking, J .

Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G.

A., Abel, E. W., Eds.; Pergamon Press: Oxford, 1982; Vol. 3, p 451.

(51) Bu¨rger, H.; Neese, H.-J . Chimia 1970, 24, 209.

(52) Bu¨rger, H.; Neese, H.-J . J . Organomet. Chem. 1969, 20, 129.

(53) Bu¨rger, H.; Kluess, C. J . Organomet. Chem. 1976, 108, 69.

(54) Da¨mmgen, U.; Bu¨rger, H. Zeit. Anorg. Allg. Chem. 1977, 429,

173.

(55) Planalp, R. P.; Andersen, R. A.; Zalkin, A. Organometallics

1983, 2, 16.

(56) Planalp, R. P.; Andersen, R. A. Organometallics 1983, 2, 1675.

3662 Organometallics, Vol. 18, No. 18, 1999

Schrock et al.

which the amide was [(Me₃Si)₂N]^-. He found (inter alia)

that [(Me₃Si)₂N]₂TiMe₂was significantly more stable

than the analogous (Me₂N)₂TiMe₂compounds prepared

by Bu¨rger. Andersen also showed that complexes of the

type [(Me₃Si)₂N]₂ZrR₂were relatively stable not only for

R ) Me but for R ) Et and documented decompositions

that involved double CH bond activation in a TMS

group.⁵⁵The greater stability of the sterically protected

TMS complexes, along with the ease of synthesizing

TMS-substituted amines, is presumably part of the

reason many explorations of group 4 amido chemistry

since then have employed TMS-substituted amido com-

plexes. (Notable exceptions are recently reported com-

plexes of the type (Cy₂N)₂TiR₂, in which R is neopentyl,

trimethylsilylmethyl, and other alkyls that do not

contain a â proton.^57,58) This is unfortunate, at least as

far as the search for olefin polymerization catalysts are

concerned, since TMS-substituted amido complexes in

general do not appear to be robust enough for chemistry

as demanding as that involved in olefin polymerizations.

(Complexes in which a dimethylsilyl group connects a

cyclopentadienyl ring and an amido nitrogen are notable

exceptions.²⁸) For example, we have found that although

[(Me₃SiN-o-C₆H₄)₂O]ZrMe₂can be prepared readily, it

cannot be activated to yield well-behaved catalysts for

the polymerization of 1-hexene.⁵⁹As Andersen showed,

CH activation is always a potential problem with TMS-

substituted amido groups, but other reactions such as

silyl migrations also might be relatively facile in some

circumstances.

The use of bidentate bisamido ligands in group 4

chemistry can be traced back to Bu¨rger,⁵⁰who studied

a variety of bidentate diamido titanium complexes,

among them complexes that contain relatively simple

[TMSNCH₂CH₂NTMS]^2-and [TMSNCH₂CH₂CH₂-

NTMS]^2-ligands, and also a variety of spirocyclic

bidentate diamido complexes. One might suspect biden-

tate diamido ligands to be relatively resistant to some

forms of decomposition compared to analogues that

contain related monodentate amido ligands, although

no direct comparisons are possible. Since 1990 a variety

of group 4 complexes have been reported that contain

bidentate diamido ligands, many of them without Si-N

bonds.^{19,30,31,33,34,42,60-79}Complexes that contain “di-

amido/donor” ligands in which the donor is in the central

position of a tridentate ligand are of relatively recent

vintage,^{33,34,60,61,65-67,70-76,80,81}especially those that do

not contain Si-N bonds.^{33,34,65-67,70,71,80,81}

There is a good deal of evidence in the recent

literature that diamido dialkyl group 4 metal complexes

can be relatively resistant toward â hydride abstraction

reactions in the alkyl groups. The instability of many

amido ligands, especially trimethylsilyl-substituted ami-

do ligands, toward reactions such as CH activation

perhaps has masked a natural resistance toward â

hydride abstraction in amido complexes. Stable dialkyl

complexes in which the alkyl contains a â proton have

begun to appear in group 4 metal chemistry in com-

plexes that contain at least one metal-amido bond.^82-86

The first stable diisobutyl complex of titanium also was

reported recently,⁶⁹and complexes of the type [C₅H₃N-

2,6-(CH₂N-2,6-i-Pr₂C₆H₃)]ZrR₂where R ) propyl or

butyl have been found to be isolable species.⁸⁷An

increase in the stability of group 4 dialkyl complexes

toward â hydride abstraction as one proceeds from Ti

to Zr to Hf that we have noted in this work is typical of

what has been found in metallocene chemistry. For

88

89

example, it is known that Cp₂TiEt₂and Cp₂TiBu₂

decompose readily, and in the presence of PMe₃, Cp₂TiEt₂

decomposes to yield Cp₂Ti(PMe₃)₂.⁴³Cp₂ZrEt₂is also not

isolable, although Cp₂HfEt₂is isolable.⁹⁰Dialkyl zir-

conocene complexes (alkyl ) Et, Pr, Bu) are known to

decompose to yield olefin adducts, which can be trapped

as PMe₃adducts.^43,91The trend toward greater stabili-

ties of dialkyl zirconocenes as the â protons become more

sterically protected and less numerous (Et < Pr < i-Bu)

has been documented by Negishi.^90,92

(70) Aizenberg, M.; Turculet, L.; Davis, W. M.; Schattenmann, F.

S.; Schrock, R. R. Organometallics 1998, 17, 4795.

(71) Schrock, R. R.; Schattenmann, F.; Aizenberg, M.; Davis, W. M.

Chem. Commun. 1998, 199.

(72) Schattenmann, F. J .; Schrock, R. R.; Davis, W. M. Organo-

metallics 1998, 17, 989.

(73) Horton, A. D.; de With, J .; van der Linden, A. J .; van de Weg,

H. Organometallics 1996, 15, 2672.

(74) Horton, A. D.; de With, J . Chem. Commun. 1996, 1375.

(75) Friedrich, S.; Schubart, M.; Gade, L. H.; Scowen, I. J .; Edwards,

A. J .; McPartlin, M. Chem. Ber. Rec. 1997, 130, 1751.

(76) Male, N. A. H.; Thornton-Pett, M.; Bochmann, M. J . Chem. Soc.,

Dalton Trans. 1997, 2487.

(77) Tsuie, B.; Swenson, D. C.; J ordan, R. F.; Petersen, J . L.

Organometallics 1997, 16, 1392.

(78) Tinkler, S.; Deeth, R. J .; Duncalf, D. J .; McCamley, A. Chem.

Commun. 1996, 2623.

(57) Minhas, R. K.; Scoles, L.; Wong, S.; Gambarotta, S. Organo-

metallics 1996, 15, 1113.

(58) Scoles, L.; Minhas, R.; Duchateau, R.; J ubb, J .; Gambarotta,

S. Organometallics 1994, 13, 4978.

(79) J eon, Y.-M.; Park, S. J .; Heo, J .; Kim, K. Organometallics 1998,

17, 3161.

(80) Gue´rin, F.; McConville, D. H.; Vittal, J . J . Organometallics

1995, 14, 3154.

(59) Schrock, R. R.; Liang, L.-C.; Baumann, R.; Davis, W. M. J .

Organomet. Chem., in press.

(60) Cloke, F. G. N.; Hitchcock, P. B.; Love, J . B. J . Chem. Soc.,

Dalton Trans. 1995, 25.

(61) Clark, H. C. S.; Cloke, F. G. N.; Hitchcock, P. B.; Love, J . B.;

Wainwright, A. P. J . Organomet. Chem. 1995, 501, 333.

(62) Cloke, F. G. N.; Geldbach, T. J .; Hitchcock, P. B.; Love, J . B. J .

Organomet. Chem. 1996, 506, 343.

(63) Herrmann, W. A.; Denk, M.; Albach, R. W.; Behm, J.; Herdtweck,

E. Chem. Ber. 1991, 124, 683.

(64) Scollard, J . D.; McConville, D. H.; Vittal, J . J . Organometallics

1995, 14, 5478.

(65) Gue´rin, F.; McConville, D. H.; Payne, N. C. Organometallics

1996, 15, 5085.

(66) Gue´rin, F.; McConville, D. H.; Vittal, J . J . Organometallics

1996, 15, 5586.

(67) Gue´rin, F.; McConville, D. H.; Vittal, J . J . Orgaometallics 1997,

16, 1491.

(81) Schrock, R. R.; Lee, J .; Liang, L.-C.; Davis, W. M. Inorg. Chim.

Acta 1998, 270, 353.

(82) Brand, H.; Arnold, J . Organometallics 1993, 12, 3655.

(83) Amor, F.; Spaniol, T. P.; Okuda, J . Organometallics 1997, 16,

4765.

(84) Amor, J . I.; Cuenca, T.; Galakhov, M.; Gomez-Sal, P.; Manza-

nero, A.; Royo, P. J . Organomet. Chem. 1997, 535, 155.

(85) Paolucci, G.; Pojana, G.; Zanon, J .; Lucchini, V.; Avtomonov,

E. Organometallics 1997, 16, 5312.

(86) Amor, F.; Butt, A.; duPlooy, K. E.; Spaniol, T. P.; Okuda, J .

Organometallics 1998, 17, 5836.

(87) Gue´rin, F. Ph.D. Thesis, University of British Columbia:

Vancouver, B. C., Canada, 1998.

(88) McDermott, J . X.; Wilson, M. E.; Whitesides, G. M. J . Am.

Chem. Soc. 1976, 98, 6529.

(89) Chang, B.-H.; Tung, H.-S.; Brubaker, C. H. Inorg. Chim. Acta

1981, 51, 143.

(90) Negishi, E.; Takahashi, T. Acc. Chem. Res. 1994, 27, 124.

(91) Buchwald, S. L.; Watson, B. T.; Huffman, J . C. J . Am. Chem.

Soc. 1987, 109, 2544.

(68) Warren, T. H.; Schrock, R. R.; Davis, W. M. Organometallics

1996, 15, 562.

(69) Warren, T. H.; Schrock, R. R.; Davis, W. M. Organometallics

1998, 17, 308.

(92) Negishi, E.; Nguyen, T.; Maye, J . P.; Choueiri, D.; Suzuki, N.;

Takahashi, T. Chem. Lett. 1992, 2367.

Ti, Zr, and Hf Diamido Complexes

Organometallics, Vol. 18, No. 18, 1999 3663

A potentially important issue for complexes that

contain diamido/donor ligands is the structure of five-

coordinate dialkyl complexes, especially when the ligand

is flexible and can form more than one type of five-

coordinate structure. We have used the structure of five-

coordinate dialkyl precursors to four-coordinate cations

as a measure of the degree of steric crowding that might

be expected in a four-coordinate cation, using the

argument that the anion will be couched on one face of

that pseudotetrahedral cation. We have been operating

on the theory that when a ligand adopts a fac coordina-

tion mode rather than a mer coordination mode in a five-

coordinate dialkyl complex, then pseudotetrahedral

four-coordinate cationic intermediates in polymerization

reactions will be relatively crowded. The failure to

prepare dineopentyl complexes, as found here, is actu-

ally a good sign that the four-coordinate cation in which

the alkyl is a growing poly(1-hexene) chain may be

crowded enough to keep the anion further away from

the metal than would be the case otherwise.

gomers.⁹⁸We propose that activated [i-PrNON]ZrMe₂

will only oligomerize 1-hexene for reasons largely trace-

able to a higher rate of â elimination, possibly from more

likely regioerrors (2,1-insertions). It is interesting to

note that complexes that contain the analogous [t-

BuNSN]^2-ligand are considerably less well-behaved

than [t-BuNON]^2-complexes in terms of polymerization

activity, even though they are predisposed to a fac

geometry as a consequence of the relatively constant

C-S-C angle (∼105°) and the reluctance of sulfur to

become planar, relative to oxygen.⁹⁹At this stage the

reason for the instability of {[t-BuNSN]ZrR}⁺complexes

relative to {[t-BuNON]ZrR}⁺complexes is not known.

We propose that the crowded tetrahedral environment

in {[t-BuNON]ZrR}⁺complexes, where R is the growing

poly(1-hexene) chain, most efficiently limits access to

the cationic metal center by a bulky, poorly coordinating

anion, encourages 1,2-insertion of 1-hexene, and dis-

courages â elimination from an alkyl derived from 1,2-

insertion. In {[t-BuNON]Zr(PhNMe₂)Me}⁺complexes

the base is likely to be less labile than in the product of

reaction with 1-hexene, so that k_iwill naturally be less

than k_p, and evidently significantly so in the case of {[t-

BuNON]Hf(PhNMe₂)Me}⁺. This may also be true of the

anion in initiators prepared in the absence of a base but

in the presence of a solvent such as chlorobenzene. The

more “open” the coordination sphere, the more tightly

the anion is likely to be associated with the cation, the

greater the probability for 2,1-insertion, and the more

opportunity for â elimination in what we presume to be

a less stable cationic alkyl complex. Polymerization of

ethylene by zirconium dimethyl complexes that contain

the rigorously planar [2,6-(ArylNCH₂)₂(C₅H₃N)]^2-lig-

and,^65,66at least when activated by MAO, was not

successful, although the reason is not yet known.¹⁰⁰The

theory that 2,1-regioerrors lead to relatively unstable

and unreactive intermediates in propylene polymeriza-

tions catalyzed by activated zirconocene alkyls has been

discussed in the literature recently.^101-105

The [t-BuNON]^2-ligand was chosen on the basis of

successful chemistry employing [d₆-t-BuNAryl]^-ligands

in early metal chemistry,^37,93-96the proposed relatively

high stability of the diphenyl ether backbone, and the

lack of any readily abstractable protons R to the nitrogen

or to the oxygen. The tert-butyl group is the largest

readily available substituent one could envision placing

on the amido nitrogen. The bulk of the tert-butyl group,

along with the planarity of the o-phenylene “arms” and

consequent interaction between two aryl protons ortho

to the oxygen (if the aryl rings lie in the same plane),

leads to a natural twisting of the backbone of the

[t-BuNON]^2-ligand, so that in five-coordinate species

that contain group 4 metals a twisted fac conformation

is preferred over the twisted mer coordination. The

[t-BuNON]^2-ligand “predisposes” five-coordinate di-

alkyl species or cationic monoalkyl species to have a

crowded, twisted fac geometry. (A five-coordinate yt-

trium complex that contains the [t-BuNON]^2-ligand in

a twisted mer coordination has been structurally char-

acterized. It was proposed that in this case the relatively

large size of yttrium(3+) allows the [t-BuNON]^2-ligand

to adopt the twisted mer conformation.⁹⁷) Interestingly,

six-coordinate cationic monoalkyl solvated species were

isolated in which the ligand had either a twisted mer

or a twisted fac orientation. In a cationic pseudotetra-

hedral {[t-BuNON]MR}⁺complex we propose that the

twisted fac conformation of the [t-BuNON]^2-ligand

becomes even more favorable in view of the likely

contraction of the metal-ligand bonds and exacerbation

of steric crowding. The importance of the tert-butyl

group is emphasized by the finding that decreasing the

size of the substituent on nitrogen from tert-butyl to

isopropyl leads to five- and six-coordinate complexes

that contain a mer form of the ligand and that activated

[i-PrNON]ZrMe₂initiators produce only 1-hexene oli-

An important feature of cations that contain a di-

amido/donor ligand is the fact that more than one site

for base (or anion) coordination to form a five-coordinate

species, and therefore also for olefin attack, is possible.

This behavior of pseudotetrahedral cations is unlike

that of pseudo-three-coordinate metallocenes, where the

resulting pseudotetrahedral transition state is basically

of only one type. The possibility of multiple and com-

petitive polymerization sites at a single metal center, a

circumstance that might also depend on the nature of

the olefin in question, is an additional complication in

the systems described here that must be taken into

account in future studies. Issues surrounding values of

(98) Baumann, R.; Stumpf, R.; Davis, W. M.; Liang, L.-C.; Schrock,

R. R. J . Am. Chem. Soc., in press.

(99) Graf, D. D.; Schrock, R. R.; Davis, W. M.; Stumpf, R. Organo-

metallics 1999, 18, 843.

(93) Laplaza, C. E.; J ohnson, M. J . A.; Peters, J . C.; Odom, A. L.;

Kim, E.; Cummins, C. C.; George, G. N.; Pickering, I. J . J . Am. Chem.

Soc. 1996, 118, 8623.

(94) Stokes, S. L.; Davis, W. M.; Odom, A. L.; Cummins, C. C.

Organometallics 1996, 15, 4521.

(100) McConville, D. H. Private communication.

(101) Busico, V.; Cipullo, R.; Chadwick, J . C.; Modder, J . F.;

Sudmeijer, O. Macromolecules 1994, 27, 7538.

(102) Busico, V.; Cipullo, R.; Talarico, G. Macromolecules 1998, 31,

2387.

(95) Laplaza, C. E.; Davis, W. M.; Cummins, C. C. Angew. Chem.,

Int. Ed. Engl 1995, 34, 2042.

(96) Odom, A. L.; Cummins, C. C.; Protasiewicz, J . D. J . Am. Chem.

Soc. 1995, 117, 6613.

(97) Graf, D. D.; Davis, W. M.; Schrock, R. R. Organometallics 1998,

17, 5820.

(103) Busico, V.; Cipullo, R.; Talarico, G.; Segre, A. L.; Caporaso, L.

Macromolecules 1998, 31, 8720.

(104) Resconi, L.; Piemontesi, F.; Balboni, D.; Sironi, A.; Moret, M.;

Rychlicki, H.; Zeigler, R. Organometallics 1996, 15, 5046.

(105) Guerra, G.; Longo, P.; Cavallo, L.; Corradini, P.; Resconi, L.

J . Am. Chem. Soc. 1997, 119, 4394.

3664 Organometallics, Vol. 18, No. 18, 1999

Schrock et al.

k_pversus k_itherefore are perhaps more complex than

might appear initially.

cessful for titanium chemistry^30,31,64have not yielded

well-behaved zirconium catalysts.¹⁰⁰The reason for this

sharp disparity is not known at this stage. However, as

far as diamido complexes of zirconium are concerned,

we suspect that a pseudo-three-coordinate cation leaves

the larger zirconium much too accessible and the alkyls

susceptible to â elimination processes, either from 1,2-

insertion products or from regioerrors (2,1-insertions).

We expect to explore some of the issues raised by this

work in future studies of {[t-BuNON]MR}⁺catalysts

and to continue to explore syntheses of other pseudo-

tetrahedral {(diamido/donor)MR}⁺species in which the

steric crowding can be maximized when R is a growing

polymer chain and in which 2,1-regioerrors thereby are

minimized and the stability toward â hydride elimina-

tion processes is maximized.

The thermal stability of the pseudotetrahedral cat-

ionic zirconium intermediates in a polymerization of

1-hexene is not high. The greater stability of the Hf

cations, at least with dimethylaniline coordinated to the

metal, probably can be ascribed to a low concentration

of four-coordinate cationic species. However, decomposi-

tion probably should not be attributed solely to irrevers-

ible â hydride elimination.³⁴The two alternative modes

of decomposition we favor at this stage are loss of a tert-

butyl radical or carbonium ion from an amido nitrogen,

as has been observed in a related diamido/phosphine

ligand system,¹⁰⁶or cleavage of the ligand backbone, as

has been observed in a recent report concerning [i-

PrNON]Ti(II) species.⁹⁸However, other possibilities

certainly cannot be excluded at this time, for example,

“direct” CH activation in a tert-butyl group to produce

isobutylene and an imido-like nitrogen.

Low-polydispersity polyolefins (as low as PDI ) 1.1)

have been obtained in the past in several early metal

catalyst systems, usually at low temperatures (-60 to

-20 °C).^107-110Molecular weights usually are relatively

low, in part as a consequence of the low temperatures

that are generally required, and often are consistent

with a low percentage of active polymerization sites.

Cobalt¹¹¹and nickel¹¹²catalysts have been discovered

recently that contain R-diimine ligands and which

appear to polymerize R-olefins in a living fashion, the

latter at -10 °C. The pyridine-based R-diimine ligand

in the nickel catalysts is strictly planar, and the

characteristics of the catalyst are controlled to a sig-

nificant degree by the steric demands of the 2,6-

disubstituted aryl groups on the imine nitrogens. Low

polydispersities are characteristic of a high rate of chain

propagation relative to chain termination, whereas a

polydispersity of 2.0 is characteristic of a polymer that

is formed from identical catalyst sites with fixed rates

of chain propagation and termination.¹¹³Polyolefins

produced from well-defined “single-site” catalysts such

as activated metallocenes typically have polydispersities

between 2.0 and 2.5.⁸It often is difficult to prove that a

process is living, unless chain initiation and chain

growth can be observed and studied directly, e.g., by

NMR techniques. That has been possible with the

system reported here and Ni¹¹²and Pd¹¹⁴systems that

contain pyridine-based R-diimine ligands. In the Ni and

Pd systems the olefin often inserts in 2,1-fashion, and

isomerizations (“chain-running”) of a coordinated olefin

are rampant.

Exp er im en ta l Section

Gen er a l P r oced u r es. Unless otherwise noted all manipu-

lations were performed under rigorous exclusion of oxygen and

moisture in a dinitrogen-filled glovebox or using standard

Schlenk procedures. Ether, THF, and pentane were sparged

with dinitrogen followed by passage through two 1 gallon

columns of activated alumina. Toluene and benzene were

distilled from benzophenone ketyl. Methylene chloride was

1

distilled from CaH₂. H NMR spectra are referenced (in ppm)

versus residual protons in the deuterated solvents as follows:

7.15 (C₆D₆), 7.27 (CDCl₃), 2.09 (toluene-d₈methyl), 7.29 (C₆D₅-

Br; most upfield resonance). ¹³C NMR spectra are referenced

as follows: 128.4 (C₆D₆), 77.2 (CDCl₃), 137.9 (toluene-d₈), 122.3

(C_ipsoin C₆D₅Br). ³¹P NMR spectra are referenced versus an

external standard of 85% H₃PO₄(δ ) 0). All NMR spectra were

taken at room temperature (∼22 °C) in C₆D₆unless otherwise

noted. Aromatic ligand resonances in ¹H and ¹³C spectra are

not assigned. Coupling constants usually are not provided

unless necessary for the identification of a compound.

Zr(NMe₂)₄,¹¹⁵Hf(NMe₂)₄,¹¹⁶TiCl₂(NMe₂)₂,¹¹⁷(2-NO₂C₆H₄)₂O,³⁵

(2-NH₂C₆H₄)₂O,³⁶and Me₃CCH₂MgCl¹¹⁸were prepared accord-

ing to literature procedures. 2,4-Dimethyl-6-nitrophenol¹¹⁹was

prepared according to a procedure reported for 2-tert-butyl-4-

methylnitrophenol.¹²⁰Zinc dust (97.5%) was purchased from

Strem and activated with 5% aqueous HCl prior to use.¹²¹PMe₃

(Strem) and 1,4-dioxane (anhydrous, Aldrich) were stored

under dinitrogen over 4 Å molecular sieves. All other reagents

were used as received. C₆D₆and toluene-d₈(Cambridge Isotope

Laboratories) were degassed with dinitrogen and dried over 4

Å molecular sieves for ∼1 day prior to use. CD₂Cl₂(Cambridge

Isotope Laboratories) was stirred over CaH₂for several days,

vacuum transferred, and stored under dinitrogen over 4 Å

molecular sieves. C₆D₅Br (Aldrich) was filtered through acti-

vated alumina and stored under dinitrogen over 4 Å molecular

sieves. Elemental analyses were performed in our laboratories

on

a Perkin-Elmer 2400 CHN analyzer or at H. Kolbe,

So far it appears that diamido/donor ligands do not

produce well-behaved titanium catalysts. Conversely,

simple arylated diamido ligands that have been suc-

Mikroanalytisches Laboratorium (Mu¨hlheim an der Ruhr,

Germany).

GPC analyses were carried out on a system equipped with

two Alltech columns (J ordi-Gell DVB mixed bed, 250 mm ×

10 mm (i.d.)). The solvent was supplied at a flow rate of 1.0

(106) Schrock, R. R.; Seidel, S. W.; Schrodi, Y.; Davis, W. M.

Organometallics 1999, 118, 428.

(107) Doi, Y.; Suzuki, S.; Soga, K. Macromolecules 1986, 19, 2896.

(108) Doi, Y.; Keii, T. Adv. Polym. Sci. 1986, 73/ 74, 201.

(109) Mashima, K.; Fujikawa, S.; Nakamura, A. J . Am. Chem. Soc.

1993, 115, 10990.

(110) Mashima, K.; Fujikawa, S.; Tanaka, Y.; Urata, H.; Oshiki, T.;

Tanaka, E.; Nakamura, A. Organometallics 1995, 14, 2633.

(111) Brookhart, M.; Desimone, J . M.; Grant, B. E.; Tanner, M. J .

Macromolecules 1995, 28, 5378.

(115) Diamond, G. M.; Rodewald, S.; J ordan, R. F. Organometallics

1995, 14, 5.

(116) Diamond, G. M.; J ordan, R. F.; Petersen, J . L. Organometallics

1996, 15, 4030.

(117) Benzing, E.; Kornicker, W. Chem. Ber. 1961, 94, 2263.

(118) Schrock, R. R.; Sancho, J .; Pederson, S. F. Inorg. Synth. 1989,

26, 44.

(112) Killian, C. M.; Tempel, D. J .; J ohnson, L. K.; Brookhart, M.

J . Am. Chem. Soc. 1996.

(113) Flory, P. J . Principles of Polymer Chemistry; Cornell University

Press: Ithaca, 1986.

(119) Hodgkinson, W. R.; Limpach, L. J . Chem. Soc. 1893, 63, 104.

(120) Stegmann, H. B.; Dumm, H. V.; Scheffer, K. Phosphorus Sulfur

1978, 5, 159.

(121) Micovic, I. V.; Ivanovic, M. D.; Piatak, D. M.; Bojic, V. D.

Synthesis 1991, 1043.

(114) Brookhart, M. Unpublished results.

Ti, Zr, and Hf Diamido Complexes

Organometallics, Vol. 18, No. 18, 1999 3665

mL/min with a Knauer HPLC pump 64. HPLC grade CH₂Cl₂

was continuously dried and distilled from CaH₂. Molecular

weights were measured using a Wyatt Technology miniDawn

three-angle detector operating at 690 nm coupled to a Knauer

differential-refractometer. The differential refractive index

increment, dn/dc, was determined assuming that all polymer

that was weighed for the run (usually ∼5 mg to (0.1 mg)

eluted from the column. To minimize polymer weighing error,

the average value for dn/dc (0.049 mL/g) from 18 runs (0.045-

0.053 mL/g) was employed, and the molecular weights were

recalculated.

C₂₀H₁₆D₁₂N₂O: C, 74.02; H, 8.70; N, 8.63. Found: C, 74.41;

H, 8.94; N, 8.30.

[2-Me(CD₃)₂CNH C₆H ₄]O[2′,4′-Me₂-6′-Me(CD₃)₂CNH C₆-

H₂](H₂[t-Bu NONMe₂]). (2-NH₂C₆H₄)O(2′,4′-Me₂-6′-NH₂C₆H₂)

(10.18 g, 44.6 mmol) was dissolved in acetone-d₆(60 g, 0.94

mol), and activated 4 Å molecular sieves (30 g) were added.

After the condensation was complete (3-7 days, as judged by

¹H NMR) the molecular sieves were filtered off and rinsed with

ether. All volatile components were removed in vacuo. The

imine dissolved in ether (80 mL) was slowly added to a

precooled solution (acetone/dry ice) of methyllithium in ether

(130 mL, 0.86 M). The reaction mixture was allowed to warm

to room temperature and stirred. After 24 h the reaction

mixture was quenched by pouring it slowly into a beaker filled

with 500 mL of a mixture of ice and water. The product was

extracted into pentane (3 × 50 mL), and the solvents were

evaporated in vacuo. The residue was redissolved in pentane

(200 mL) and filtered through a ∼40 cm long and 2.5 cm wide

alumina column. The product was eluted with more pentane

(400 mL). The pentane was evaporated in vacuo to afford a

viscous pale yellow oil; yield 8.43 g (54%): ¹H NMR (CDCl₃) δ

7.01 (d, 1), 6.86 (t, 1), 6.70 (s, 1), 6.54 (t, 1), 6.40 (m, 2), 4.43

(s, 1, NH), 3.87 (s, 1, NH), 2.30 (s, 3, ArMe), 2.00 (s, 3, ArMe),

1.43 (s, 3, C(CD₃)₂Me), 1.26 (s, 3, C(CD₃)₂Me); ¹³C NMR (CDCl₃)

δ 146.1, 140.2, 139.3, 136.6, 134.6, 130.9, 122.0, 120.2, 117.6,

116.1, 114.5, 112.6, 51.4 (C(CD₃)₂Me), 51.0 (C(CD₃)₂Me), 30.3

(C(CD₃)₂Me), 30.1 (C(CD₃)₂Me), 29.9 (m, C(CD₃)₂Me), 21.8

(ArMe), 16.5 (ArMe); HRMS (EI) calcd for C₂₂H₂₀D₁₂N₂O

352.326785; found 352.32679. Anal. Calcd for C₂₂H₂₀D₁₂N₂O:

C, 74.94; H, 9.15; N, 7.94. Found: C, 74.91; H, 9.14; N, 7.96.

2-Eth yl-6-n itr op h en ol. To a cooled (0 °C) and vigorously

stirred solution of 34.00 g (0.4 mol) NaNO₃and 1.760 g (4

mmol) of La(NO₃)₃‚6H₂O in 640 mL of a 1:1 mixture of

concentrated HCl and water was added a solution of 48.88 g

(0.4 mol) of 2-ethylphenol in 500 mL of diethyl ether over a

period of 20 min.¹²²The reaction was stirred for 2.5 h at 0 °C

until no more starting material could be detected by TLC. The

phases were separated, and the aqueous phase was extracted

twice with 200 mL of diethyl ether. The combined organic

phases were dried with Na₂SO₄, and the diethyl ether was

removed in vacuo. The dark yellow oil was subjected to

chromatography on silica with hexane first as an eluent, with

gradually increasing amounts of CH₂Cl₂. Only the first yellow

fraction was collected. All volatile components were removed

in vacuo to leave a yellow-orange oil; 26.82 g (0.16 mol, 40%):

¹H NMR δ 10.95 (s, 1), 7.97 (d, 1), 7.46 (d, 1), 6.91 (t, 1), 2.75

(q, 2), 1.26 (t, 3); ¹³C NMR δ 153.5, 136.6, 135.2, 133.5, 122.5,

119.5, 23.0, 13.6.

6-Eth yl-2,2′-d in itr od ip h en yl Eth er . A mixture of 2-ethyl-

6-nitrophenol (16.72 g, 0.1 mol), 2-fluoronitrobenzene (14.11

g, 0.1 mol), and anhydrous K₂CO₃(27.64 g, 0.2 mol) was heated

in 100 mL of DMSO to 100 °C for 48 h. The mixture was

poured into 500 mL of ice water. After 2 h the tan precipitate

was filtered off and washed with water until the washings

were colorless. The residue was dried in vacuo and recrystal-

lized from 30 mL of boiling methanol to give a tan powder;

15.51 g (0.054 mol, 54%): ¹H NMR (CDCl₃) δ 7.97 (d, 1), 7.63

(d, 1), 7.45-7.38 (m, 2), 7.15 (t, 1), 6.60 (d, 1), 2.64 (q, 2), 1.21

(t, 3): ¹³C NMR (CDCl₃) δ 151.1, 144.2, 143.2, 140.8, 139.1,

135.3, 134.4, 126.8, 126.4, 124.0, 122.6, 115.6, 23.4, 14.1. (Due

to impurities, these chemical shifts are not completely reliable.)

6-Eth yl-2,2′-d ia m in od ip h en yl Eth er . In a pressure bottle,

15.14 g (52.5 mmol) of 6-ethyl-2,2′-dinitrodiphenyl ether was

suspended in 50 mL of degassed ethanol, and 0.75 g of 10%

Pd on activated carbon was added. The bottle was purged with

N₂three times and then pressurized with dihydrogen while

stirring the solution. The pressure was adjusted to 40 psi, and

the bottle was heated to 70 °C for 16 h. After the bottle had

(2-NO₂-C₆H₄)O(2′,4′-Me₂-6′-NO₂-C₆H₂). A 1 L one-neck

flask was charged with 2,4-dimethyl-6-nitrophenol (47.5 g, 0.28

mol), 2-fluoronitrobenzene (40.0 g, 0.28 mol), K₂CO₃(80.0 g,

0.58 mol), and DMSO (500 mL). The reaction mixture was

stirred at 100 °C under an atmosphere of dinitrogen for 48 h.

The dark red slurry was allowed to cool to room temperature

and then poured onto ice/water (1.5 L). A beige solid im-

mediately precipitated from the red solution. The mixture was

stirred for 30 min and then filtered. The solid was liberally

washed with water and dried in vacuo; yield 68.1 g (83%). The

crude product was used for subsequent reactions without

further purification. Recrystallization from hot methanol gave

analytically pure tan needles: ¹H NMR (CDCl₃) δ 8.01 (d, 1),

7.71 (s, 1), 7.42 (m, 2), 7.15 (t, 1), 6.63 (d, 1), 2.44 (s, 3, Me),

2.22 (s, 3, Me); ¹³C NMR (CDCl₃, only 11 aromatic resonances

were identified) δ 150.8, 142.9, 142.2, 139.1, 137.5, 137.0,

134.4, 126.2, 124.0, 122.4, 115.7, 20.8, 16.2. Anal. Calcd for

C

₁₄H₁₂N₂O₅: C, 58.33; H, 4.20; N, 9.72. Found: C, 58.53; H,

4.22; N, 9.66.

(2-NH₂C₆H₄)O(2′,4′-Me₂-6′-NH₂C₆H₂). A Fischer-Porter

bottle was charged with (2-NO₂C₆H₄)O(2′,4′-Me₂-6′-NO₂C₆H₂)

(60.7 g, 0.21 mol), Pd/C (3.00 g, 10% Pd), and ethanol (500

mL). The slurry was stirred under dihydrogen (35 psi) at 65

°C for 24 h. The mixture was cooled to room temperature and

filtered through Celite. The initially colorless filtrate turned

orange upon exposure to air. All volatile components were

removed in vacuo, leaving a light orange/brown solid or

occasionally an orange oil; yield 46.9 g (98%). The crude

product was used for subsequent reactions without further

purification. It slowly darkens in air and is therefore best

stored under dinitrogen. It may be crystallized as large off-

white blocks by slow evaporation of a saturated ether solu-

tion: ¹H NMR (CDCl₃) δ 6.82 (m, 2), 6.59 (dd, 1), 6.47 (m, 3),

4.0 (br s, 2, NH₂), 3.66 (br s, 2, NH₂), 2.26 (s, 3, Me), 2.07 (s,

3, Me); ¹³C NMR (CDCl₃) δ 144.8, 139.5, 138.0, 135.9, 135.3,

131.5, 122.4, 121.5, 118.7, 115.8, 114.9, 112.8, 21.2, 16.1. Anal.

Calcd for C₁₄H₁₆N₂O: C, 73.66; H, 7.06; N, 12.27. Found: C,

73.69; H, 7.21; N, 12.43.

[2-Me(CD₃)₂CNHC₆H₄]₂O (H₂[t-Bu NON]). (2-NH₂C₆H₄)₂O

(18.8 g, 94 mmol) was dissolved in acetone-d₆(120 g, 1.87 mol),

and activated 4 Å molecular sieves (30 g) were added. After

the condensation was complete (3-7 days, as judged by ¹H

NMR) the molecular sieves were filtered off and rinsed with

ether. All volatile components were removed from the ether

solution of the ligand in vacuo. The imine dissolved in ether

(60 mL) was slowly added to a precooled solution (acetone/dry

ice) of methyllithium in ether (270 mL, 0.88 M). The reaction

mixture was allowed to warm to room temperature and stirred.

After 24 h the reaction mixture was quenched by pouring it

slowly into a beaker filled with 500 mL of a mixture of ice

and water. The product was extracted into hexane (3 × 100

mL), and the combined organic layers were filtered through a

∼35 cm long and 2.5 cm wide alumina column. The solvent

was evaporated in vacuo to afford a viscous orange oil; yield

16.7 g (55%): ¹H NMR (CDCl₃) δ 7.00 (m, 4), 6.68 (m, 4), 4.19

(br s, 2, NH), 1.35 (s, 6, C(CD₃)₂Me); ¹³C NMR (CDCl₃) δ 145.24,

138.34, 123.62, 117.76, 117.30, 115.96, 50.81 (C(CD₃)Me), 29.81

(C(CD₃)₂Me), 29.28 (m, C(CD₃)₂Me); HRMS (EI) calcd for

(122) Ouertani, M.; Girard, P.; Kagan, H. B. Tetrahedron Lett. 1982,

23, 4315.

C

₂₀H₁₆D₁₂N₂O 324.295485; found 324.29549. Anal. Calcd for

3666 Organometallics, Vol. 18, No. 18, 1999

Schrock et al.

reached room temperature, the ethanol was removed in vacuo.

The residue was dissolved in 75 mL of diethyl ether, and the

solution was cooled to -60 °C. A tan precipate formed, which

was filtered off using a precooled (-78 °C) frit. The residue

was dried in vacuo. The product contains ∼10% of an uniden-

tified impurity that contains one ethyl group; 6.30 g (27 mmol,

53% if pure product): ¹H NMR (CDCl₃) δ 7.03 (t, 1), 6.83 (dt,

2), 6.70 (dt, 2), 6.63 (dt, 1), 6.44 (d, 1), 4.02 (s, br, 2), 3.70 (s,

br, 2), 2.51 (q, 2), 1.15 (t, 3); ¹³C NMR (CDCl₃) δ 151.0, 144.0,

143.1, 140.6, 139.0, 135.4, 134.5, 126.8, 126.2, 123.9, 122.6,

115.5, 23.1, 14.0.

6-Eth yl-2,2′-d ia m in od ip h en yl Eth er Aceton ed iim in e-

d ₆. 6-Ethyl-2,2′-diaminodiphenyl ether (6.30 g, 27 mmol) was

dissolved in 20.0 g (310 mmol) of acetone-d₆. Activated 4 Å

molecular sieves (15 g) were added, and the mixture was

stirred for 16 h. The solution was filtered, and the molecular

sieves were thoroughly washed with 150 mL of diethyl ether.

The solvents were removed in vacuo to give an orange oil; 7.97

g (25 mmol, 96%): ¹H NMR (CDCl₃) δ 7.09 (t, 1), 6.98 (d, 1),

6.85 (dt, 1), 6.73-6.61 (m, 2), 6.42 (d, 1), 2.52 (q, 2), 2.19 (m,

1), 1.93 (m, 1), 1.85 (m, 1), 1.73 (m, 1), 1.13 (t, 3).

6-Eth yl-2,2′-bis(d ₆-ter t-bu tyla m in o)d ip h en yl Eth er . A

solution of 7.97 g (25 mmol) in 25 mL of diethyl ether was

slowly added to 100 mL of a 0.7 M solution of methyllithium

(obtained by dilution of 50 mL of a 1.4 M solution with 50 mL

of diethyl ether) in diethyl ether (70 mmol) at -78 °C. The

mixture was allowed to reach room temperature, was stirred

for 16 h, and then was poured on 200 mL of ice. The phases

were separated, and the aqueous phase was extracted with

150 mL of pentane. The combined organic phases were dried

with Na₂SO₄, and the solvents were removed in vacuo. The

dark green oil was purified by chromatography on silica with

pentane/CH₂Cl₂mixtures of gradually increasing polarity as

the eluent. The first yellow fraction was collected, and the

solvents were removed in vacuo to give an orange oil; 3.27 g

(10 mmol, 39%): ¹H NMR (CDCl₃) δ 7.05 (t, 2), 6.89 (t, 2), 6.64

(d, 1), 6.53 (t, 1), 6.42 (d, 1), 4.46 (s, 1), 3.92 (s, 1), 2.44 (dm,

2), 1.45 (s, ∼4), 1.27 (s, ∼4), 1.13 (t, 3); ¹³C NMR (CDCl₃) δ

146.2, 140.7, 140.4, 137.3, 136.5, 125.4, 122.2, 117.6, 116.0,

113.5, 112.6, ≈ 51.2, 30.0, 23.3, 14.7.

[t-Bu NON]TiMe₂. A solution of MeMgCl in THF (3.0 M,

350 µL) was added to a solution of [t-BuNON]TiCl₂(230 mg,

0.52 mmol) in ether (10 mL) at -35 °C. The color immediately

changed from dark purple to orange, and a white solid

precipitated. The mixture was stirred for 15 min without

further cooling. All volatile components were removed in vacuo,

and the residue was extracted with pentane (∼10 mL) over a

period of ∼5 min. The mixture was filtered through Celite,

and the pentane was removed from the filtrate in vacuo to

afford an orange-red solid, which was recrystallized from a

mixture of ether and pentane at -35 °C; yield 162 mg (78%):

¹H NMR δ 6.87 (m, 6), 6.56 (m, 2), 1.60 (s, 6, TiMe₂) 1.42 (s, 6,

C(CD₃)₂Me); ¹³C NMR δ 148.5, 143.5, 126.1, 122.1, 121.4, 119.3,

64.6 (TiMe₂), 60.2 (C(CD₃)₂Me), 31.4 (C(CD₃)₂Me), 30.9 (m,

C(CD₃)₂Me). Anal. Calcd for C₂₂H₂₀D₁₂N₂OTi: C, 65.98; H, 8.05;

N, 6.99. Found: C, 66.07; H, 7.94; N, 6.84.

[t-Bu NON]Zr (NMe₂)₂. H₂[t-BuNON] (6.48 g, 20 mmol) and

Zr(NMe₂)₄(5.34 g, 20 mmol) were dissolved in pentane (40 mL).

Colorless crystals precipitated over a period of 2 days at 22

°C and were filtered off (6.9 g). The supernatant was concen-

trated and cooled to -35 °C overnight, yielding a second crop

of colorless solid (1.15 g); total yield 8.05 g (80%): ¹H NMR δ

6.97 (m, 6), 6.55 (m, 2), 2.94 (s, 12, NMe₂), 1.33 (s, 6,

C(CD₃)₂Me); ¹³C NMR δ 147.8, 145.7, 125.6, 122.4, 118.3, 117.8,

57.0 (C(CD₃)₂Me), 43.6 (NMe₂), 32.1 (C(CD₃)₂Me), 32.0 (m,

C(CD₃)₂Me). Anal. Calcd for C₂₄H₂₆D₁₂N₄OZr: C, 57.43; H,

7.57; N, 11.16. Found: C, 57.56; H, 7.76; N, 11.16.

[t-Bu NON]Zr Cl₂. Me₃SiCl (1.5 g, 13.74 mmol) was added

to a suspension of [t-BuNON]Zr(NMe₂)₂(2.295 g, 4.58 mmol)

in ether (50 mL). The reaction mixture was stirred at room

temperature for 20 h. All volatile components were removed

from the mixture in vacuo, and the yellow solid was washed

with pentane (10 mL) and dried; yield 2.06 g (93%). An

analytically pure sample was obtained by crystallization from

ether. For alkylation reactions the crude material was used

without further purification: ¹H NMR δ 6.79 (m, 6), 6.54 (m,

2), 1.29 (s, 6H, C(CD₃)₂Me); ¹³C NMR δ 147.1, 141.0, 127.4,

122.8, 122.4, 118.9, 58.7 (C(CD₃)₂Me), 30.6 (C(CD₃)₂Me), 30.1

(m, C(CD₃)₂Me). Anal. Calcd for C₂₀H₁₄Cl₂D₁₂N₂OZr: C, 49.77;

H, 5.43; N, 5.80. Found: C, 49.84; H, 5.21; N, 5.68.

[t-Bu NON]Ti(NMe₂)₂. A solution of butyllithium in hexane

(4.2 mL, 1.6 M) was added to a solution of H₂[t-BuNON] (1.09

g, 3.36 mmol) in ether (30 mL) at -35 °C. The mixture was

warmed to room temperature and stirred for 4 h. A suspension

of TiCl₂(NMe₂)₂(696 mg, 3.36 mmol) in ether (20 mL) was

added to the solution containing the Li₂[t-BuNON] at -35 °C.

The mixture was warmed to room temperature and stirred for

15 h. The mixture was filtered through Celite, and all volatile

components were removed from the filtrate in vacuo. The

residue was dissolved in a minimum of methylene chloride and

layered with pentane. The mixture was cooled to -35 °C to

afford an orange crystalline solid; yield 864 mg (56%). An

analytically pure sample was obtained by recrystallization

from ether: ¹H NMR δ 6.92 (m, 6), 6.63 (m, 2), 3.13 (s, 12,

NMe₂), 1.28 (s, 6, C(CD₃)₂Me); ¹³C NMR δ 150.9, 147.1, 124.37,

123.3, 120.3, 118.6, 60.2 (m, C(CD₃)₂Me), 47.8 (NMe₂), 32.4

(C(CD₃)₂Me), 31.9 (m, C(CD₃)₂Me). Anal. Calcd for C₂₄H₂₆D₁₂N₄-

OTi: C, 62.86; H, 8.35; N, 12.22. Found: C, 62.85; H, 8.34; N,

12.14.

[t-Bu NON]TiCl₂. A Schlenk tube was charged with [t-

BuNON]Ti(NMe₂)₂(379 mg, 0.83 mmol), Me₃SiCl (270 mg, 2.49

mmol), and toluene (10 mL). The solution was heated to 110

°C for 7 days, during which time the solution turned black-

purple. The volatile components were removed in vacuo, and

the residue was recrystallized from a mixture of methylene

chloride and pentane at -35 °C; yield 286 mg (78%): ¹H NMR

δ 6.84 (m, 4), 6.57 (m, 4), 1.33 (s, 6, C(CD₃)₂Me); ¹³C NMR δ

147.8, 142.1, 126.7, 124.4, 120.6, 118.9, 64.8 (m, C(CD₃)₂Me),

30.6 (C(CD₃)₂Me), 30.4 (m, C(CD₃)₂Me). Anal. Calcd for

[t-Bu NON]Zr I₂. A Schlenk tube was charged with [t-

BuNON]Zr(NMe₂)₂(3.5 g, 7.0 mmol), methyl iodide (15 g, 106

mmol), and toluene (100 mL). The pale yellow solution was

heated to 50 °C for 2 days, during which time white Me₄NI

precipitated from the reaction and the color of the solution

turned bright orange. The Me₄NI was filtered off, the solvents

were removed from the filtrate in vacuo, and the residue was

washed with pentane (10 mL) to afford a yellow solid. The

crude product can be recrystallized from toluene layered with

pentane, but was used in subsequent reactions without further

purification; yield 4.14 g (89%): ¹H NMR δ 6.79 (m, 6), 6.56

(m, 2), 1.36 (br s, 6, C(CD₃)₂CH₃); ¹³C NMR (C₆D₆, 70 °C) δ

146.8, 139.4, 127.9, 124.0, 123.3, 119.4, 60.2 (m, C(CD₃)₂CH₃),

31.3 (C(CD₃)₂CH₃), 30.7 (m, C(CD₃)₂CH₃). Anal. Calcd for

C

₂₀H₁₄D₁₂I₂N₂OZr: C, 35.98; H, 3.93; N, 4.20. Found: C, 35.71;

H, 3.94; N, 3.88.

[t-Bu NONMe₂]Zr (NMe₂)₂. A solution of H₂[t-BuNONMe₂]

(5.00 g, 14.2 mmol) and Zr(NMe₂)₄(3.79 g, 14.2 mmol) in

toluene (40 mL) was heated in a sealed Schlenk tube to 105

°C for 3 days. All volatile components were then removed in

vacuo. Recrystallization of the light orange residue from

pentane at -25 °C produced pale yellow microcrystalline

material in 4 crops; yield 4.97 g (66%): ¹H NMR δ 7.13 (d, 1),

6.88 (t, 1), 6.72 (s, 1), 6.62 (d, 1), 6.53 (t, 1), 6.35 (s, 1), 3.15 (s,

6, NMe₂), 2.82 (s, 6, NMe₂), 2.21 (s, 3, ArMe), 2.17 (s, 3, ArMe),

1.51 (s, 3, C(CD₃)₂Me), 1.20 (s, 3, C(CD₃)₂Me); ¹³C NMR δ 149.4,

146.3, 144.2, 143.0, 135.6, 130.4, 124.2, 122.5, 121.4, 120.8,

119.4, 113.3, 57.5 (m, C(CD₃)₂Me), 56.7 (m, C(CD₃)₂Me), 45.3

(NMe₂), 42.3 (NMe₂), 32.3 (C(CD₃)₂Me), 32.1 (C(CD₃)₂Me), 31.7

(m, C(CD₃)₂Me), 22.3 (ArMe), 16.6 (ArMe). Anal. Calcd for

C

₂₀H₁₄D₁₂Cl₂N₂OTi: C, 54.43; H, 5.89; N, 6.35. Found: C,

54.57; H, 5.96; N, 6.13.

Ti, Zr, and Hf Diamido Complexes

Organometallics, Vol. 18, No. 18, 1999 3667

C₂₆H₃₀D₁₂N₄OZr: C, 58.93; H, 7.99; N, 10.57. Found: C, 59.21;

H, 8.10; N, 10.38.

was extracted with pentane (20 mL) for 15 min. The extract

was filtered, and the pentane was removed in vacuo. The

residue was recrystallized from ether at -25 °C to produce

pale yellow crystals; yield 664 mg (72%).

[t-Bu NONMe₂]Zr Cl₂. Me₃SiCl (2.55 g, 23.5 mmol) was

added to a suspension of [t-BuNONMe₂]Zr(NMe₂)₂(4.59 g, 8.66

mmol) in ether (60 mL). After stirring the mixture at room

temperature for 20 h all volatile components were removed in

vacuo, leaving an analytically pure, bright yellow powder (4.31

g, 97%): ¹H NMR δ 6.77 (m, 2), 6.52 (s, 1), 6.47 (d, 2), 6.38 (s,

1), 2.18 (s, 3, ArMe), 2.0 (s, 3, ArMe), 1.53 (s, 3, C(CD₃)₂Me),

1.12 (s, 3, C(CD₃)₂Me); ¹³C NMR δ 149.2, 141.9, 141.0, 139.0,

131.6, 125.8, 125.3, 122.3, 121.9, 120.9, 114.6 (only 11 aroamat-

ic resonances were observed), 59.2 (C(CD₃)₂Me), 58.2 (C(CD₃)₂-

Me), 30.9 (C(CD₃)₂Me), 30.5 (C(CD₃)₂Me), 30.0 (m, C(CD₃)₂Me),

22.0 (ArMe), 16.9 (ArMe). Anal. Calcd for C₂₂H₁₈D₁₂Cl₂N₂OZr:

C, 51.54; H, 5.90; N, 5.46. Found: C, 51.88; H, 6.07; N, 5.47.

[t-Bu NONEt]Zr (NMe₂)₂. A 1.763 g (5 mmol) sample of

6-ethyl-2,2′-bis([d₆]-tert-butylamino)diphenyl ether and 1.334

g (5 mmol) of Zr(NMe₂)₄were dissolved in 25 mL, and the

mixture was heated in a sealed Schlenk tube at 100 °C for 24

h. The toluene was removed in vacuo, and the residue was

recrystallized from pentane to give orange crystals; 1.724 g

(3.25 mmol, 65%): ¹H NMR δ 7.10 (t, 1), 6.99 (t, 1), 6.87-6.79

(m, 2), 6.61-6.46 (m, 3), 3.12 (s, 6), 2.82 (s, 6), 2.79 (dt, 1),

2.55 (dt, 1), 1.15 (s, ∼4), 1.19 (t, 3), 1.18 (s, ∼4); ¹³C NMR δ

149.3, 146.8, 144.3, 143.9, 136.9, 126.8, 124.2, 122.7, 120.8,

119.5, 117.9, 113.3, ∼57.3, 45.4, 42.2, 32.2, 23.5, 14.9.

[t-Bu NONMe₂]Zr Me₂. A solution of MeMgI in ether (3.0

M, 1.3 mL) was added to a suspension of [t-BuNONMe₂]ZrCl₂

(1.00 g, 1.95 mmol) in ether (20 mL) at -25 °C. The reaction

mixture was stirred for 5 min without further cooling. All

volatile solvents were then removed in vacuo, and the residue

was extracted with pentane (20 mL) for 5 min. The extract

was filtered, and the pentane was removed from the filtrate

in vacuo. Crystallization of the foamy, very soluble residue

from a concentrated solution of ether/pentane (∼1-2 mL) at

-25 °C produced analytically pure, pale yellow, somewhat

waxy material; yield 503 mg (55%): ¹H NMR δ 6.92-6.77 (m,

3), 6.56-6.38 (m, 3), 2.15 (s, 3, ArMe), 2.11 (s, 3, ArMe), 1.63

(s, 3, C(CD₃)₂Me), 1.16 (s, 3, C(CD₃)₂Me), 0.89 (s, 3, ZrMe), 0.81

(s, 3, ZrMe); ¹³C NMR δ 149.6, 142.9, 142.5, 141.8, 137.5, 131.6,

124.5, 123.7, 122.4, 120.4, 119.5, 114.9, 57.3 (C(CD₃)₂Me), 56.7

(C(CD₃)₂Me), 45.7 (ZrMe), 44.1 (ZrMe), 31.5 (C(CD₃)₂Me), 31.1

(m, C(CD₃)₂Me), 30.7 (C(CD₃)₂Me), 22.1 (ArMe), 17.0 (ArMe).

Anal. Calcd for C₂₄H₂₄D₁₂N₂OZr: C, 61.09; H, 7.69; N, 5.94.

Found: C, 61.12; H, 8.06; N, 6.08.

[t-Bu NON]Zr Et₂. A solution of EtMgBr in ether (3.0 M,

1.4 mL) was added to a suspension of [t-BuNON]ZrCl₂(1.00

g, 2.07 mmol) in ether (20 mL) at -25 °C. The reaction mixture

was stirred for 5 min without further cooling. All volatile

solvents were then removed in vacuo, and the residue was

extracted with cold pentane (20 mL) over a period of 5 min.

The extract was filtered through Celite, and the pentane was

removed from the filtrate in vacuo. Recrystallization of the

residue from ether at -25 °C produced pale yellow crystals;

yield 549 mg (56%): ¹H NMR δ 6.90 (m, 6), 6.54 (m, 2), 1.60

(t, 6, ZrCH₂CH₃), 1.37 (s, 6, CMe(CD₃)₂), 1.18 (q, 4, ZrCH₂CH₃);

¹³C NMR δ 148.53, 143.30, 126.43, 122.67, 120.08, 119.45,

59.98, 57.18, 31.16 (C(CD₃)₂Me), 30.59 (m, C(CD₃)₂Me), 13.86

(ZrCH₂CH₃). Anal. Calcd for C₂₄H₂₄D₁₂N₂OZr: C, 61.09; H,

7.69; N, 5.94. Found: C, 61.41; H, 7.73; N, 6.02.

[t-Bu NON]Zr P r ₂. A solution of PrMgCl in ether (2.0 M,

2.1 mL) was added to a suspension of [t-BuNON]ZrCl₂(1.00,

2.07 mmol) in ether (20 mL) at -25 °C. The reaction mixture

was stirred for 5 min without further cooling. All volatile

solvents were then removed in vacuo, and the residue was

extracted with cold pentane (20 mL). After 5 min the extract

was filtered and the pentane was reduced in volume in vacuo

to a pale yellow oil (∼1 mL). Ether (∼1 mL) was added. Cooling

this solution to -35 °C overnight yielded 527 mg (51%) of a

pale yellow solid. The precise assignment of ¹H and ¹³C

resonances is uncertain: ¹H NMR δ 6.90 (m, 6), 6.54 (m, 3),

1.93 (m, 4), 1.37 (s, 6, CMe(CD₃)₂), 1.25 (m, 4), 1.08 (t, 6, ZrCH₂-

CH₂CH₃); ¹³C NMR δ 148.51, 143.23, 126.45, 122.76, 120.13,

119.48, 72.50 (ZrCH₂CH₂CH₃), 57.24, 31.20 (C(CD₃)₂Me), 30.39

(m, C(CD₃)₂Me), 23.96, 21.30. Anal. Calcd for C₂₆H₂₈D₁₂N₂-

OZr: C, 62.47; H, 8.06; N, 5.60. Found: C, 62.74; H, 8.34; N,

5.65.

[t-Bu NON]Zr (i-Bu )₂. A solution of i-BuMgCl in ether (2.0

M, 950 µL) was added to a suspension of [t-BuNON]ZrCl₂(462

mg, 954 µmol) in ether (12 mL) at approximately -35 °C. The

reaction mixture was stirred for 5 min without further cooling.

All volatile solvents were then removed in vacuo, and the off-

white residue was extracted with pentane (10 mL). After 5

min two drops of 1,4-dioxane were added. The extract was

filtered, and the pentane was reduced in volume in vacuo to a

pale yellow oil (∼1 mL). Ether (∼1 mL) was added. This

solution was stored at -35 °C overnight and produced 244 mg

(49%) of analytically pure pale yellow, waxy solid: ¹H NMR

(C₆D₅Br) δ 6.95 (m, 6), 6.63 (m, 2), 2.24 (sept, 2, CH₂CH(CH₃)₂)

1.38 (s, 6, CMe(CD₃)₂), 1.18 (d, 4, CH₂CH(CH₃)₂), 1.01 (d, 12,

CH₂CH(CH₃)₂); ¹³C NMR (C₆D₅Br) δ 147.52, 142.29, 125.8,

121.9, 119.4, 118.7, 81.5 (CH₂CHMe₂, 56.7 (C(CD₃)₂Me), 30.8

(C(CD₃)₂Me), 30.2 (m, C(CD₃)₂Me), 28.5 (CH₂CHMe₂). The

[t-Bu NONEt]Zr Cl₂. A 1.152 g (2.2 mmol) sample of [t-

BuNONEt]Zr(NMe₂)₂and 0.6 g (5.5 mmol) of Me₃SiCl were

dissolved in 10 mL of diethyl ether, and the mixture was

stirred for 17 h. All volatile components were removed, and

repeated coevaporation with pentane gave a yellow powder;

1.083 g (2.1 mmol, 96%): ¹H NMR δ 6.93 (t, 1), 6.82-6.60 (m,

4), 6.45 (m, 2), 2.76 (dt, 1), 2.40 (dt, 1), 1.50 (s, ∼4), 1.21 (t, 3),

1.11 (s, ∼4); ¹³C NMR δ 148.9, 142.6, 141.7, 139.8, 138.1, 129.3,

125.4, 123.0, 121.9, 121.9, 121.0, 114.6, 58.8, 30.2, 24.3, 14.9.

[t-Bu NONEt]Zr Me₂. A 1.02 g (2.0 mmol) sample of [t-

BuNONEt]ZrCl₂was dissolved in 20 mL of diethyl ether, and

1.33 mL (3 M solution in diethyl ether, 2.0 mmol) of MeMgBr

was added. After 10 min all volatile components were removed

in vacuo, and the residue was extracted with 20 mL of pentane.

The solution was filtered through Celite, and the pentane was

removed in vacuo. The residue was recrystallized from 5-7

mL of pentane to give large colorless crystals; 0.738 g (1.5

mmol, 78%): ¹H NMR δ 7.03 (t, 1), 6.93-6.79 (m, 3), 6.67 (d,

1), 6.53 (d, 1), 6.43 (d, 1), 2.73 (dt, 1), 2.40 (dt, 1), 1.62 (s, ∼4),

1.15 (t, 3), 1.14 (s, ∼4), 0.88 (s, 3), 0.81 (s, 3); ¹³C NMR δ 149.4,

144.1, 142.7, 142.4, 138.2, 124.6, 121.8, 121.0, 120.5, 119.6,

114.9, ∼57.0, 45.8, 44.6, 30.7, 24.3, 15.2. Anal. Calcd for

C

₂₄H₂₄D₁₂N₂OZr: C, 61.09; H, 7.69; N, 5.94. Found: C, 61.18;

H, 7.76; N, 6.05.

[t-Bu NON]Zr Me₂. (a ) F r om [t-Bu NON]Zr I₂. A solution

of MeMgI in ether (2.8 M, 2.3 mL) was added to a suspension

of [t-BuNON]ZrI₂(2.119 g, 3.17 mmol) in ether (50 mL) at -35

°C. The reaction mixture was allowed to warm to room

temperature and was stirred until the yellow solid was

replaced by white precipitate (∼30 min). All volatile solvents

were then removed in vacuo, and the off-white residue was

extracted with pentane (50 mL). The extract was filtered, and

the pentane was removed in vacuo. The crude product was

recrystallized from a mixture of pentane and ether to afford

pale yellow crystals; yield 1.02 g (72%): ¹H NMR δ 6.90 (m,

6), 6.53 (m, 2), 1.36 (s, 6, C(CD₃)₂Me), 0.84 (s, 6, ZrMe₂); ¹³C

NMR δ 148.1, 142.9, 126.5, 122.5, 120.1, 119.3, 57.0 (C(CD₃)₂-

Me), 45.6 (ZrMe₂), 31.1 (C(CD₃)₂Me), 30.6 (m, C(CD₃)₂Me).

Anal. Calcd for C₂₂H₂₀D₁₂N₂OZr: C, 59.54; H, 7.21; N, 6.31.

Found: C, 59.81; H, 7.19; N, 6.39.

(b) F r om [t-Bu NON]Zr Cl₂. A solution of MeMgI in ether

(3.0 M, 1.4 mL) was added to a suspension of [t-BuNON]ZrCl₂

(1.00 g, 2.07 mmol) in ether (20 mL) at -25 °C. The reaction

mixture was stirred for 5 min without further cooling. All

volatile solvents were then removed in vacuo, and the residue

3668 Organometallics, Vol. 18, No. 18, 1999

Schrock et al.

resonance for CH₂CHMe₂was not observed. Anal. Calcd for

-40 °C as colorless prisms; yield 7.405 g (77%): ¹H NMR δ

6.94-6.83 (m, 6, Ar), 6.54 (m, 2, Ar), 1.36 (s, 6, t-Bu), 0.65 (s,

6, Me); ¹³C{¹H} NMR δ 126.66, 123.15, 119.93, 119.15, 57.01.

Anal. Calcd for C₂₂H₂₀N₂D₁₂HfO: C, 49.76; H, 6.07; N, 5.27.

Found: C, 49.62, 49.66; H, 5.97, 5.90; N, 5.18, 5.21.

[t-Bu NON]Hf(¹³CH₃)₂. This complex was prepared in an

analogous manner to that employed to prepare [t-BuNON]-

HfMe₂from [t-BuNON]HfCl₂(1.43 g, 2.50 mmol) and ¹³CH₃-

MgI (5.00 mmol, 1.54 M in ether; prepared from equimolar

amounts of ¹³CH₃I and Mg in ether) in 17 mL of ether at -40

°C; yield 670 mg (50%): ¹H NMR δ 6.94-6.83 (m, 6, Ar), 6.54

(m, 2, Ar), 1.36 (s, 6, t-Bu), 0.65 (d, 6, ¹J _CH) 112, Me); ¹³C{¹H}

NMR δ 56.32 (¹³CH₃).

C

₂₈H₃₂D₁₂N₂OZr: C, 63.70; H, 8.40; N, 5.31. Found: C, 63.92;

H, 8.69; N, 5.28.

[t-Bu NON]Zr (CH₂CMe₃)Cl. A solution of Me₃CCH₂MgCl

in ether (1.35 M, 840 µL) was added to a suspension of

[t-BuNON]ZrCl₂(543 mg, 1.12 mmol) in ether (10 mL) at -25

°C. The reaction mixture was allowed to warm to room

temperature and stirred for 30 min. All volatile components

were removed in vacuo, and the residue was extracted with

pentane (20 mL) over a period of 10 min. The extract was

filtered, and the filtrate was concentrated to ∼3 mL. Pale

yellow microcrystals began to form. The mixture was stored

at -25 °C overnight; yield 414 mg (71%): ¹H NMR δ 6.87 (m,

4), 6.80 (d, 2), 6.52 (m, 2), 1.64 (s, 2, CH₂CMe₃), 1.36 (s, 6,

C(CD₃)₂Me), 1.08 (s, 9, CH₂CMe₃); ¹³C NMR δ 146.7, 142.3,

127.3, 122.6, 120.4, 118.8, 87.9 (CH₂CMe₃), 57.6 (CCD₃)₂Me),

35.3 (CH₂CMe₃), 34.5 (CH₂CMe₃), 31.1 (C(CD₃)₂Me), 30.6

(C(CD₃)₂Me). Anal. Calcd for C₂₅H₂₅D₁₂ClN₂OZr: C, 57.71; H,

7.17; N, 5.38. Found: C, 57.88; H, 7.16; N, 5.36.

[t-Bu NON]Zr (η²-C₂H₄)(P Me₃)₂. To a solution of [t-BuNON]-

ZrEt₂(149 mg, 316 µmol) in ether (2 mL) neat PMe₃(185 mg,

2.434 mmol) was added. The reaction mixture was shaken for

a few seconds and then stored at -25 °C. After 38 h red

crystals were separated and dried in vacuo; yield 160 mg

(85%): ¹H NMR (toluene-d₈) δ 7.23 (d, 2), 6.85 (t, 2), 6.75 (d,

2), 6.37 (t, 2), 1.43 (br s, 2, CH^AH^BCH^ACH^B), 1.23 (br s, CH^AH^B-

CH^ACH^B), 1.08 (s, 6, C(CD₃)₂Me), 0.87 (d, J _PH) 3 Hz, 18,

PMe₃); ¹³C NMR (toluene-d₈, 0 °C) δ 148.60, 145.22, 124.64,

118.09, 114.03, 112.65, 53.22 (C(CD₃)₂Me), 46.45 (s, C₂H₄),

30.93 (C(CD₃)₂Me), 16.23 (s, PMe₃); ³¹P (0 °C) δ -29.9 (br s).

Anal. Calcd for C₂₈H₃₆D₁₂N₂OP₂Zr: C, 56.62; H, 8.15; N, 4.72.

Found: C, 57.01; H, 8.27; N, 4.59.

[t-Bu NON]Hf(NMe₂)₂. H₂[t-BuNON] (22.87 g, 0.070 mol)

and Hf(NMe₂)₄(25.00 g, 0.070 mol) were dissolved in 30 mL

of toluene, and the solution was heated slowly. Rapid gas

evolution was observed, and a microcrystalline product sub-

sequently precipitated from solution. The resulting mixture

was kept at 100-105 °C for 16 h. It was then cooled to 22 °C,

and the volatile components were removed in vacuo. The white

microcrystalline solid was slurried in 40 mL of pentane,

collected on a frit, washed with several portions of pentane,

and dried in vacuo; yield 33.90 g (82%): ¹H NMR δ 7.06 (m, 2,

Ar), 6.97 (m, 2, Ar), 6.90 (m, 2, Ar), 6.56 (m, 2, Ar), 3.01 (s, 12,

NMe₂), 1.34 (s, 6, t-Bu); ¹³C{¹H} NMR δ 147.73, 145.30, 125.79,

123.28, 118.51, 117.91, 57.18 (C(CD₃)₂CH₃), 43.33 (N(CH₃)₂),

32.23 (C(CD₃)₂CH₃), 31.69 (m, C(CD₃)₂CH₃). Anal. Calcd for

[t-Bu NON]HfEt₂. EtMgBr (7.28 mmol, 3.00 M in ether) was

added dropwise to a stirred suspension of [t-BuNON]HfCl₂

(2.00 g, 3.47 mmol) in 60 mL of ether at -40 °C. The mixture

was allowed to warm to 25 °C over 2 h, after which 1,4-dioxane

(∼2 mL) was added. The resulting mixture was stirred for an

additional 10 min and filtered through Celite, and the filtrate

was stripped to dryness in vacuo. The residue was dissolved

in ether (7 mL), and the solution was stored at -40 °C.

Colorless crystals separated from the mother liquor were

collected and washed quickly with pentane and dried in vacuo;

yield 1.535 g (79%): ¹H NMR δ 7.01-6.80 (m, 6), 6.55 (m, 2),

1.78 (t, 6, CH₂CH₃), 1.36 (s, 6, t-Bu), 0.97 (q, 4, CH₂CH₃);

¹³C{¹H} NMR δ 148.08, 142.82, 126.59, 123.43, 120.02, 119.30,

70.26 (CH₂CH₃), 56.92, 31.47, 30.02, 14.14 (CH₂CH₃). Anal.

Calcd for C₂₄H₂₄N₂D₁₂HfO: C, 51.56; H, 8.65; N, 5.01. Found:

C, 51.72; H, 6.74; N, 5.35.

[t-Bu NON]Hf(CH₂CHMe₂)₂. A stirred suspension of [t-

BuNON]HfCl₂(3.00 g, 5.20 mmol) in 50 mL of ether at -40

°C was treated with i-BuMgCl (10.400 mmol, 2.0 M in ether).

The mixture was allowed to warm to 25 °C over 2 h, after

which 1,4-dioxane (∼3 mL) was added and the mixture was

stirred for an additional 30 min. The mixture was filtered

through Celite, and the filtrate was stripped to dryness. The

crude product was dissolved in pentane (30 mL), and the

solution was filtered. The filtrate was concentrated in vacuo

and stored at -40 °C. Large colorless prisms separated from

the mother liquor and were collected and dried in vacuo; yield

2.49 g (78%): ¹H NMR δ 7.02-6.85 (m, 6, Ar), 6.56 (m, 2, Ar),

2.43 (m, 2, CH₂CHC(CH₃)₂), 1.37 (s, 6, t-Bu), 1.16 (d, 12, CH₂-

CHC(CH₃)₂, 1.02 (d, 4, CH₂CHC(CH₃)₂, J _HH) 6.9); ¹³C{¹H}

NMR δ 148.29, 142.77, 126.64, 123.73, 120.18, 119.48, 92.22,

31.57, 31.35, 30.81 (m, CD₃), 29.84. Anal. Calcd for C₂₈H₃₂N₂D₁₂-

HfO: C, 54.66; H, 7.21; N, 4.55. Found: C, 54.85; H, 7.39; N,

4.48.

C

₂₄H₂₆N₄D₁₂OHf: C, 48.93; H, 6.50; N, 9.51. Found: C, 49.08;

H, 6.54; N, 9.51.

[t-Bu NON]Hf(CH₂CMe₃)Cl. A stirred suspension of [t-

BuNON]HfCl₂(3.28 g, 5.69 mmol) in 50 mL of ether at -40

°C was treated dropwise with Me₃CCH₂MgCl (5.69 mmol, 3.16

M in ether), and the mixture was allowed to warm to room

temperature over a period of 2 h. 1,4-Dioxane (∼3 mL) was

added, and the mixture was stirred for another 15 min and

then filtered through Celite. The filtrate was stripped to

dryness, dissolved in a mixture of ether and pentane, and

filtered again. The filtrate was stored at -40 °C. Colorless

crystals of the product were collected, washed with pentane,

and dried in vacuo; yield 3.00 g (87%): ¹H NMR δ 6.90 (m, 4),

6.81 (m, 2), 6.51 (m,2), 1.38 (m, 14, t-Bu), 1.34 (s, 2, CH₂C-

(CH₃)₃)), 1.10 (s, 9, CH₂C(CH₃)₃); ¹³C{¹H} NMR δ 146.31,

141.90, 127.42, 123.11, 120.01, 118.54, 92.13 (CH₂C(CH₃)₃),

57.10 (CH₂C(CH₃)₃), 56.95 (m, C(CD₃)₂CH₃), 35.28 (CH₂C-

(CH₃)₃), 31.41 (s, C(CD₃)₂CH₃), 30.88 (m, C(CD₃)₂CH₃). Anal.

Calcd for C₂₅H₂₅N₂ClD₁₂HfO: C, 49.42; H, 6.14; N, 4.61.

Found: C, 49.28; H, 6.25; N, 4.51.

[t-Bu NON]HfCl₂. [t-BuNON]Hf(NMe₂)₂(33.90 g, 57.54

mmol) and Me₃SiCl (25.00 g, 230.2 mmol) were dissolved in

125 mL of toluene in a 250 mL round-bottom Schlenk flask.

The stirred mixture was heated to 100 °C, whereupon all solids

dissolved. After 16 h, the solution was cooled to 22 °C and

volatile components were removed in vacuo. The pale yellow

solid was slurried in 100 mL of pentane, collected by filtration,

washed with 2 × 30 mL of pentane, and dried in vacuo; yield

31.445 g (96%). Analytically pure samples were recrystallized

from ether at -40 °C: ¹H NMR δ 6.80 (m, 6, Ar), 6.53 (m, 2,

Ar), 1.31 (s, 6, t-Bu); ¹³C{¹H} NMR δ 146.89 (b), 140.71, 127.58

(b), 123.31 (b), 121.74, 118.81 (b), 57.79 (C(CD₃)₂CH₃), 31.01

(C(CD₃)₂CH₃), 30.46 (m, C(CD₃)₂CH₃). Anal. Calcd for C₂₀H₁₄N₂-

Cl₂D₁₂HfO: C, 42.00; H, 4.58; N, 4.90; Cl, 12.40. Found: C,

42.16; H, 4.60; N, 4.86; Cl, 12.81.

[t-Bu NON]HfMe₂. A stirred solution of [t-BuNON]HfCl₂

(10.41 g, 18.21 mmol) in 100 mL of ether at -40 °C was treated

with MeMgI (38.24 mmol, 3.0 M in ether). The mixture was

allowed to warm to 25 °C over 1 h, after which 1,4-dioxane

(∼5 mL) was added and the mixture was stirred for an

additional 50 min. The mixture was filtered through Celite,

and the volatile components were removed from the filtrate

in vacuo. The crude material was crystallized from ether at

[t -Bu NON]H f(CH₂CMe₃)Me. A stirred solution of [t-

BuNON]Hf(CH₂CMe₃)Cl (1.35 g, 2.23 mmol) in 15 mL of ether

at -40 °C was treated dropwise with MeMgI (2.34 mmol, 3.0

M in ether), and the mixture was stirred at room temperature

for 16 h. 1,4-Dioxane (1 mL) was added, and the mixture was

stirred for an additional 30 min and filtered through Celite.

Ti, Zr, and Hf Diamido Complexes

Organometallics, Vol. 18, No. 18, 1999 3669

The filtrate was stripped to dryness in vacuo. The crude

product was recrystallized from pentane at -40 °C as small

white crystals; yield 949 mg (73%): ¹H NMR δ 6.95 (m, 4),

6.84 (m,2), 6.54 (m, 2), 1.38 (s, 6, t-Bu), 1.24 (s, 2, CH₂C(CH₃)₃),

1.06 (s, 9, CH₂C(CH₃)₃), 0.82 (s, 3, HfMe); ¹³C{¹H} NMR δ

147.47, 142.81, 126.71, 123.29, 119.78, 119.26, 95.12 (CH₂C-

(CH₃)₃), 62.68 (HfMe), 56.95 (CH₂C(CH₃)₃), 56.60 (m, C(CD₃)₂-

CH₃), 35.65 (CH₂C(CH₃)₃), 31.43 (C(CD₃)₂CH₃), 31.18 (m,

C(CD₃)₂CH₃).

1.15 (s, 6, t-Bu), 0.89 (d, 3, HfMe, J _CH) 111 Hz); ¹³C{¹H} NMR

(C₆D₅Br) δ 64.91 (HfMe).

{[t-Bu NON]HfMe(THF )₂}BP h ₄. A light blue mixture of

[t-BuNON]HfMe₂(700 mg, 1.318 mmol), [Cp′₂Fe]BPh₄(703 mg,

1.318 mmol), and THF (209 mg, 2.900 mmol) in 15 mL of

toluene was stirred for 16 h. A pale green solid was collected

on a fine frit and was washed with 2 × 3 mL toluene followed

by 2 × 1 mL of pentane. The crude product was dissolved in

THF, and a small amount of white solid was filtered off. The

product was crystallized from THF/pentane at -40 °C as an

off-white microcrystalline solid, which was washed with pen-

tane and dried in vacuo; yield 805 mg, 62%): ¹H NMR (CD₂Cl₂)

δ 7.40-6.70 (m, 8), 7.31 (br, 8, o-H), 7.02 (m, 8, m-H), 6.89 (m,

4, p-H), 4.14/3.80 (bs, 8, THF), 1.76 (m, 8, THF), 1.61 (m,

t-Bu_mer), 1.40 (m, t-Bu_fac), 0.72 (s, Me_mer), 0.55 (s, Me_fac); ¹³C{¹H}

NMR (CD₂Cl₂) δ 164.46 (q, C_ipso, J _CB) 49 Hz), 147.51 (b),

143.61, 142.72, 136.36 (C_meta), 127.59 (b), 126.33, 126.07 (C_ortho),

122.18 (C_para), 121.68 (b), 120.89, 120.12, 117.97, 113.85, 76.67

(THF), 62.14 (Me_fac), 60.57 (Me_mer), 57.43 (br, C(CD₃)₂CH₃, fac),

56.45 (br, C(CD₃)₂CH₃, mer), 30.77 (m, C(CD₃)₂CH₃), 25.99/

25.81 (THF). Anal. Calcd for C₅₃H₅₃N₂BD₁₂HfO₃: C, 64.86; H,

6.68; N, 2.86. Found: C, 64.88; H, 6.80; N, 2.82.

{[t-Bu NON]HfMe(DME)}BP h ₄. A light blue mixture of

[t-BuNON]HfMe₂(1.500 g, 2.824 mmol), [Cp′₂Fe]BPh₄(1.506

g, 2.824 mmol), and DME (305 mg, 3.389 mmol) in 50 mL of

toluene was stirred for 18 h. An off-white solid was collected

on a fine frit and was washed with 3 × 5 mL of toluene followed

by 3 × 2 mL of pentane. The crude product was dissolved in

15 mL of CH₂Cl₂, and a small amount of white solid was

filtered off. The product was crystallized from CH₂Cl₂at -40

°C as a white microcrystalline solid, which was washed with

pentane and dried in vacuo; yield 1.658 g (63%): ¹H NMR

(CD₂Cl₂) δ 7.35 (br, 8, o-H), 7.24-6.80 (m, 20), 3.57 (s, 6), 3.04

(m, 2), 2.70 (m, 2), 1.34 (s, 6), 0.51 (s, 3, Me); ¹³C{¹H} NMR

(CD₂Cl₂) δ 164.45 (q, C_ipso, J _CB) 49 Hz), 146.53, 140.70, 136.35

(C_meta), 127.83, 126.32 (C_ortho), 122.74, 122.45, 121.87 (C_para),

119.66, 73.47 (OMe), 67.84 (HfMe), 58.54 (CH₂O), 57.67 (m,

C(CD₃)₂CH₃), 30.65 (C(CD₃)₂CH₃), 30.02 (m, C(CD₃)₂CH₃).

Anal. Calcd for C₄₉H₄₇N₂BD₁₂HfO₃: C, 63.60; H, 6.43; N, 3.02.

Found: C, 63.06; H, 6.54; N, 3.00.

Obser vation of {[(t-Bu N-d₆-o-C₆H₄)(d₆-t-Bu NH-o-C₆H₄)O]-

HfMe₂}[B(C₆F ₅)₄]. A solution of [t-BuNON]HfMe₂(20 mg,

0.038 mmol) in 0.5 mL of C₆D₅Br at -40 °C was combined with

a suspension of [PhNMe₂(H)][B(C₆F₅)₄] (30 mg, 0.038 mmol)

in 0.5 mL of C₆D₅Br at 22 °C, whereupon the solids dissolved

and the color rapidly turned pale green. The solution was kept

at -40 °C for 20 min, then quickly transferred to an NMR

tube, which was flame-sealed and kept at -196 °C until placed

into an NMR probe precooled to -35 °C: ¹H NMR (C₆D₅Br,

-35 °C) δ 7.2 6.0 (m, 13), 4.33 (s, 1, NH), 2.53 (s, 6, Me₂NPh),

1.06 (s, 3, t-Bu), 1.03 (s, 3, t-Bu), 0.55 (s, 3, HfMe), 0.53 (s, 3,

HfMe). The spectrum also contained resonances for [t-BuNON]-

HfMe(PhNMe₂)}[B(C₆F₅)₄] and CH₄(0.16 ppm).

Obser vation of {[(t-Bu N-d₆-o-C₆H₄)(d₆-t-Bu NH-o-C₆H₄)O]-

HfEt₂}[B(C₆F ₅)₄]. [t-BuNON]HfEt₂(15 mg, 0.027 mmol) and

[PhNMe₂(H)][B(C₆F₅)₄] (21 mg, 0.027 mmol) were rapidly

dissolved in 0.8 mL of CD₂Cl₂. The solution was transferred

rapidly to an NMR tube, which was flame-sealed and then kept

at 0 °C until placed into an NMR probe at 22 °C: ¹H NMR

(CD₂Cl₂) δ 7.60-6.60 (m, 14), 4.64 (s, 1, NH), 2.93 (s, 6, Me₂-

NPh), 1.78 (t, 3, CH₂CH₃), 1.61 (s, 3, t-Bu), 1.20 (m, 2,

CH₂CH₃), 1.19 (t, 3, CH₂CH₃) 1.08 (s, 3, t-Bu), 0.87 (m, 2,

CH₂CH₃). The solution also contained C₂H₆(δ 0.85) and

resonances for [t-BuNON]HfCl(Et)(PhNMe₂): δ 7.65 (m, 3),

7.51 (m, 2), 7.17 (m, 6), 6.80 (m, 2), 3.66 (s, 6, Me₂NPh), 1.38

(s, 6, t-Bu), 1.28 (t, 3, CH₂CH₃), 0.69 (q, 2, CH₂CH₃).

{[t-Bu NON]Zr Me}[MeB(C₆F ₅)₃]. A solution of B(C₆F₅)₃(35

mg, 67 µmol) in pentane (5 mL) that had been cooled to -35

°C was added to a solution of [t-BuNON]ZrMe₂(30 mg, 67

µmol) in pentane (5 mL). The mixture immediately turned

bright yellow. A solid precipitated when the B(C₆F₅)₃solution

was added at -35 °C, but it dissolved when the mixture was

warmed to room temperature. The slightly cloudy bright yellow

solution was stirred at room temperature for 5 min, filtered,

and cooled to -35 °C for 2 days. Yellow crystals were filtered

off and briefly dried in vacuo; yield 31 mg (47%): ¹H NMR

(C₆D₅Br) δ 7.03-6.55 (m, 8), 2.24 (br s, 3, BMe), 0.98 (s, 6,

CMe(CD₃)₂), 0.77 (s, 3, ZrMe); ¹³C NMR (toluene-d₈, -30 °C) δ

150.24, 147.16, 141.5 (m, C₆F₅), 139.5 (m, C₆F₅), 137.77, 135.8

(m, C₆F₅), 123.54, 59.20, 50.90 (s, ZrMe), 29.5 (br m, t-Bu,

B-Me); ¹⁹F NMR (C₆D₆) δ -133.14 (d, 6, F_o), -159.35 (br s, 3,

F_p), -164.27 (t, 6, F_m).

Obser va tion of {[t-Bu NON]Zr Me(P h NMe₂)]}[B(C₆F ₅)₄].

Solid [t-BuNON]ZrMe₂(∼8 mg, 18 µmol) was added to a

suspension of [PhNMe₂H][B(C₆F₅)₄] (15 mg, 18 µmol) in C₆D₅-

Br (1 mL) at -35 °C, and the mixture was stirred for 30 min

at room temperature: ¹H NMR (C₆D₅Br) δ 6.94-6.50 (m, 13),

2.74 (s, 6, PhNMe₂), 1.17 (s, 6, C(CD₃)₂Me), 0.95 (s, 3, ZrMe);

¹⁹F NMR (C₆D₅Br) -131.78 (F_o), -162.11 (t, F_p), -165.94 (br

m, F_m); ¹³C NMR (C₆D₅Br) δ 55.88 (ZrMe).

{[t -Bu NON]Zr Me(TH F )₂]}[B(C₆F ₅)₄]. [Ph₃C][B(C₆F₅)₄]

(0.230 g, 0.249 mmol) was added to a -35 °C solution of (t-

BuNON)ZrMe₂(0.110 g, 0.248 mmol) in 3 mL of C₆H₅Cl. The

solution was allowed to stand for ∼5 min or until the [Ph₃C]-

[B(C₆F₅)₄] entirely dissolved. To this dark yellow solution was

added 0.04 mL (0.493 mmol) of THF. The solution immediately

lightened to bright yellow. The product was precipitated as a

bright yellow powder by the addition of 10 mL of pentane to

the C₆H₅Cl solution; yield 0.222 g (72%): ¹H NMR (C₆D₅Br) δ

1.03, 1.5-1.8 (br m), 3.9 (br, THF); ¹³C NMR (C₆D₅Br) δ 53.4,

55.6 (Zr¹³CH₃). When this reaction was repeated in C₆D₅Br,

crystals of [(t-BuNON)ZrMe(THF)₂][B(C₆F₅)₄] formed when

THF was added. It should be noted that the direct reaction of

(t-BuNON)ZrMe₂with [Ph₃C][B(C₆F₅)₄] in THF yielded a

polymeric product, most likely poly(THF). The addition of

[Ph₃C][B(C₆F₅)₄] to THF will also produce poly(THF), as will

the dissolution of [(t-BuNON)ZrMe(THF)₂][B(C₆F₅)₄] in THF,

although the latter reaction is much slower.

{[t-Bu NON]Zr Me(DME)]}[B(C₆F ₅)₄]. In a 10 mL round-

bottom flask 0.102 g (0.082 mmol) of [[t-BuNON]ZrMe(ether)₂]-

[B(C₆F₅)₄] was dissolved in 1 mL of DME. The bright yellow

solution was stirred for 5 min, and then 10 mL of pentane was

added. Golden yellow crystals precipitated from solution and

were isolated via filtration; yield 0.085 g (87%): ¹H NMR (C₆D₅-

Br, 500 MHz) δ 1.01 (3, ZrMe), 1.58 (∼6, t-Bu), 3.62 (2,

OCH₂CH₂O), 3.78 (6, CH₃O), 3.86 (2, OCH₂CH₂O); ¹³C NMR

(C₆D₅Br, 125 MHz); δ 52.47 (Zr(¹³CH₃)).

Obser va tion of {[t-Bu NON]HfMe(P h NMe₂)}[B(C₆F ₅)₄].

Solid [t-BuNON]HfMe₂(15 mg, 0.028 mmol) and [PhNMe₂H]-

[B(C₆F₅)₄] (22 mg, 0.028 mmol) were dissolved in 0.7 mL of

C₆D₅Br by stirring for 30 min to give a pale lime-colored

solution: ¹H NMR (C₆D₅Br) δ 6.8-7.3 (m, 14, Ar), 2.79 (s, 6,

Me₂NPh), 1.15 (s, 6, t-Bu), 0.89 (s, 3, HfMe).

Obser vation of {[(t-Bu N-d₆-o-C₆H₄)(d₆-t-Bu NH-o-C₆H₄)O]-

Hf(i-Bu )₂}[B(C₆F₅)₄]. [t-BuNON]Hf(i-Bu)₂(20 mg, 0.033 mmol)

and [PhNMe₂(H)][B(C₆F₅)₄] (26 mg, 0.033 mmol) were rapidly

dissolved in 0.8 mL of CD₂Cl₂. The solution was transferred

rapidly to an NMR tube, which was flame-sealed and then kept

{[t-Bu NON]Hf(¹³CH₃)(P h NMe₂)}[B(C₆F ₅)₄] was prepared

in an analogous manner from [t-BuNON]Hf(¹³CH₃)₂(15 mg,

0.028 mmol) and [PhNMe₂H][B(C₆F₅)₄] (22 mg, 0.028 mmol):

¹H NMR (C₆D₅Br) δ 6.8-7.3 (m, 14, Ar), 2.79 (s, 6, Me₂NPh),

3670 Organometallics, Vol. 18, No. 18, 1999

Schrock et al.

at 0 °C until placed into an NMR probe at 22 °C: ¹H NMR

(CD₂Cl₂) δ 7.60-7.07 (m, 10, Ar), 6.80 (m, 3, Ar), 4.49 (s, 1,

NH), 2.93 (s, 6, Me₂NPh), 2.41 (m, 1, CH₂CH(CH₃)₂), 1.62 (s,

3, t-Bu), 1.52 (m, 1, CH₂CH(CH₃)₂), 1.22 (m, 2, CH₂CH(CH₃)₂),

1.21 (s, 3, t-Bu), 1.10 (m, 2, CH₂CH(CH₃)₂), 1.02 (d, 3), 0.97

(d, 3), 0.81 (d, 3), 0.66 (d, 3). The solution also contained

isobutane (δ 0.70 (d, 9), the methyne proton was not located)

and a small amount of isobutylene (δ 4.61 (m) and 1.72 (m)).

Resonances for [t-BuNON]HfCl(i-Bu)(PhNMe₂): δ 7.65 (m, 3),

7.51 (m, 2), 7.17 (m, 6), 6.80 (m, 2), 3.66 (s, 6, Me₂NPh), 1.75

(m, CH₂CHC(CH₃)₂), 1.38 (s, 6, t-Bu), 0.89 (d, 6, CH₂CHC-

(CH₃)₂), 0.80 (d, 2, CH₂CHC(CH₃)₂).

mL, 1.0 M). Most solvent was removed at 15 Torr (water

aspirator) at 60 °C. The viscous oil was dried at 60 mTorr at

80 °C for 20 h. The yields were essentially quantitative (97-

100%).

X-r a y Cr ysta l Stu d ies. All data were collected on Bruker

Platform diffractometer equipped with a CCD area detector

and driven by the SMART¹²³suite of programs using Mo/KR

radiation, λ ) 0.71073 Å. Data reduction was carried out with

SAINT,¹²³while SHELXTL¹²³was used to solve and refine both

structures. Patterson methods were employed to locate the

heavy atoms in each instance, while subsequent difference

Fourier calculations revealed the positions of the remaining

non-hydrogen atoms. Those atoms were treated as anisotropic

scatterers. Hydrogen atoms were placed in calculated positions

and were allowed to ride upon their respective non-hydrogen

atoms. Crystal data and structure refinement data can be

found in Tables 1 and 2.

P olym er iza tion of 1-Hexen e Usin g {[t-Bu NON]Zr Me-

(P h NMe₂)]}[B(C₆F ₅)₄]. In

a typical experiment varying

amounts of hexene (0.3-3.0 mL) were added to a solution of

{[t-BuNON]ZrMe(PhNMe₂)]}[B(C₆F₅)₄] (∼50 µmol of [PhNMe₂H]-

[B(C₆F₅)₄] and ∼1.1 equiv of [t-BuNON]ZrMe₂) in chloroben-

zene at 0 °C). The carefully weighed, limiting reagent was the

“activator”, [PhNMe₂H][B(C₆F₅)₄]. It is assumed that the

amount of catalyst formed is equal to the amount of activator

when it is added to a 10% excess of [t-BuNON]ZrMe₂in

chlorobenzene. ([t-BuNON]ZrMe₂itself was found to be inac-

tive.) The total volume of the reaction mixture was always 13.0

mL. The reaction mixture was stirred for 1.5 h and quenched

by addition of HCl in diethyl ether (4 mL, 1.0 M). Most solvent

was removed at 15 Torr (water aspirator) at 45 °C. The viscous

oil was dried at 100 mTorr at 50-60 °C for 20 h. The yields

were essentially quantitative (97-100%). The molecular weights

and polydispersities were measured by light scattering. The

average value for dn/dc (0.049 mL/g) obtained (assuming total

elution) from 18 runs (0.045-0.053 mL/g) was employed and

M_n(found) calculated using that basis.

Ack n ow led gm en t. R.R.S. thanks the Department

of Energy (DE-FG02-86ER13564) for supporting this

research. R.S. thanks the Alexander von Humboldt

Foundation for a Feodor-Lynen-Fellowship, while R.B.

thanks the Studienstiftung des Deutschen Volkes for a

predoctoral fellowship.

Su ppor tin g In for m ation Available: Fully labeled ORTEP

drawings, atomic coordinates, bond lengths and angles, and

anisotropic displacement parameters for [t-BuNON]ZrCl₂,

[t-BuNON]ZrMe₂, [t-BuNON]Zr(η²-C₂H₄)(PMe₃)₂, {[t-BuNON]-

ZrMe(THF)₂}[B(C₆F₅)₄], and {[t-BuNON]ZrMe(DME)}[B(C₆F₅)₄].

(Supporting Information for [t-BuNON]TiMe₂and {[t-BuNON]-

ZrMe}[MeB(C₆F₅)₃] were provided for the preliminary publica-

tion of this material.³³) This material is available free of charge

via the Internet at http://pubs.acs.org.

P olym er iza tion of 1-Hexen e Usin g {[t-Bu NON]HfMe-

(P h NMe₂)}[B(C₆F₅)₄]. In a typical experiment varying amounts

of 1-hexene (0.3-3.0 mL) were added to a solution of {[t-

BuNON]HfMe(PhNMe₂)}[B(C₆F₅)₄] (prepared from ∼75 µmol

of [PhNMe₂H][B(C₆F₅)₄] and ∼1 equiv of [t-BuNON]HfMe₂in

chlorobenzene at 22 °C). The reaction mixture was stirred for

1-6 h and quenched by addition of HCl in diethyl ether (3

OM9905005

(123) SMART, SAINT, and SHELXTL are part of the 1995 Bruker

Analytical X-ray Systems software, Madison, WI.

Article Doi

Synthesis of titanium, zirconium, and hafnium complexes that contain diamido donor ligands of the type [(t-BuN-o-C6H4)2O]2- and an evaluation of activated versions for the polymerization of 1-hexene

DOI: 10.1021/om9905005

Source and publish data:

Authors:

Article abstract of DOI:10.1021/om9905005

Full text of DOI:10.1021/om9905005

Products guided by the article

R&D Labs maybe for 247938-64-3

Relevant to this article

Hot Product