Preparation and activation of complexes of the type [((mesityl)NCH2CH2)2NX]ZrMe2 (X = H, Me) with [Ph3C][B(C6F5)4] or [PhNMe2H][B(C6F5

Organometallics 2000, 19, 5325-5341

5325

P r ep a r a tion a n d Activa tion of Com p lexes of th e Typ e

[((m esityl)NCH₂CH₂)₂NX]Zr Me₂(X ) H, Me) w ith

[P h ₃C][B(C₆F ₅)₄] or [P h NMe₂H][B(C₆F ₅)₄]

Richard R. Schrock,* Arturo L. Casado, J onathan T. Goodman,

Lan-Chang Liang, Peter J . Bonitatebus, J r., and William M. Davis

Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue,

Cambridge, Massachusetts 02139

Received J une 13, 2000

The zirconium dimethyl complexes [N₂NX]ZrMe₂(N₂NX ) [(MesNCH₂CH₂)₂NX]; Mes )

mesityl; X ) H (1a ), Me (1b)), have “mer” structures in the solid state in which the amido

nitrogens occupy “axial” positions in a trigonal bipyramid. The reaction of 1b with 1 equiv

of [Ph₃C][B(C₆F₅)₄] followed by addition of diethyl ether yielded the ether adduct {[N₂NMe]-

ZrMe(Et₂O)}⁺(with [B(C₆F₅)₄]^-as the anion), an X-ray study of which revealed it to be a fac

trigonal-bipyramidal species in which the diethyl ether is coordinated in an apical position.

The reaction of 1b with 1 equiv of [PhNMe₂H][B(C₆F₅)₄] led to {[N₂NMe]ZrMe(NMe₂Ph)}-

[B(C₆F₅)₄], solution NMR studies of which suggest a structure analogous to that of {[N₂NMe]-

ZrMe(Et₂O)}⁺. Heating solutions of {[N₂NMe]ZrMe(NMe₂Ph)}[B(C₆F₅)₄] led to C-H activation

in one mesityl o-methyl group and formation of methane. The reaction of 1b with 0.5 equiv

of [Ph₃C][B(C₆F₅)₄] yielded [{[N₂NMe]ZrMe}₂(µ-Me)][B(C₆F₅)₄] (5b), an X-ray diffraction study

of which revealed an almost linear (167.4°) methyl bridge linking two distorted TBP moieties

through the apical positions (average Zr-C(bridge) ) 2.48 Å, average Zr-C(terminal) )

2.24 Å). The equatorial methyl groups in 5b exchange readily between Zr centers, while the

bridging methyl group and the equatorial methyl groups exchange relatively slowly on the

NMR time scale, but still rapidly on the chemical time scale. Exchange of free [N₂NMe]-

ZrMe₂with the [N₂NMe]ZrMe₂fragment in 5b is also facile on the chemical time scale. The

reaction of 1b with 1.0 equiv or more of [Ph₃C][B(C₆F₅)₄] led to formation of a cationic species

(6b), two forms of which could be observed at low temperature. Activation of 1a with [Ph₃C]-

[B(C₆F₅)₄] yielded only one cationic form of 6a at low temperatures. Exchange of methyl

groups between 6a and 6b is slow on the chemical time scale. All evidence is consistent

with the observation of different ion pairs of 6b at low temperatures.

In tr od u ction

class of group 4 metal diamido complexes that are

being explored for early-transition-metal chemistry,

often with the goal of preparing new olefin polymeri-

zation catalysts.^14-46We have found that dimethyl

Dialkylzirconium(IV) complexes that contain di-

amido/donor ligands, e.g., [(t-Bu-N-o-C₆H₄)₂O]^{2- 1-3}

,

[(MesNCH₂CH₂)₂NR]^2-(Mes ) mesityl; R ) H, Me),⁴

and others,^5-13have been prepared and studied recently

in our laboratory. They are members of a growing

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

R. J . Am. Chem. Soc. 1999, 121, 7822.

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

Organomet. Chem. 1999, 591, 163.

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69.

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1997, 119, 9, 3830.

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1998, 17, 989.

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1996, 15, 5085.

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1996, 15, 5586.

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metallics 1999, 118, 428.

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metallics 1999, 18, 843.

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Publication on Web 11/11/2000

5326 Organometallics, Vol. 19, No. 25, 2000

Schrock et al.

complexes that contain a diamido/donor ligand in which

oxygen is the central donor can be activated with

[PhNMe₂H][B(C₆F₅)₄] or [Ph₃C][B(C₆F₅)₄] to give cat-

ionic complexes that will polymerize 1-hexene effi-

ciently. In the case of the [(t-Bu-N-o-C₆H₄)₂O]^2-system,

the polymerization occurs in a living fashion below

∼10 °C via 1,2-insertions into the Zr-C bond, as shown

by ¹³C labeling¹and kinetic⁴⁷studies. Ligands that

pared by the palladium-catalyzed reaction^48-51between

2 equiv of mesityl bromide and diethylenetriamine. A

reliable method of preparing dimethyl complexes that

contain the [N₂NH]^2-ligand involves the reaction of

H₂[N₂NH] with Zr(NMe₂)₄to yield [N₂NH]Zr(NMe₂)₂.

Treatment of [N₂NH]Zr(NMe₂)₂with Me₃SiCl yields

[N₂NH]ZrCl₂, which upon treatment with CH₃MgX

(X ) Cl, Br, I) affords [N₂NH]ZrMe₂. Treatment of

[N₂NH]ZrMe₂(1a ) with methyllithium followed by

methyl iodide was found to yield [N₂NMe]ZrMe₂(1b).⁴

It is also possible to prepare either 1a or 1b in one pot

directly from H₂[N₂NH] and ZrCl₄via methylation of

the initial adduct, “{H₂[N₂NH]}ZrCl₄”, with 4 equiv of

CH₃MgI (to give 1a ) or with 5 equiv of methyllithium

followed by methyl iodide (to give 1b). Alternatively,

H₂[N₂NMe] can be prepared directly from H₂[N₂NH] in

∼80% yield by treating it with MeI in acetonitrile at

room temperature in the presence of potassium carbon-

ate (eq 1). [N₂NMe]ZrMe₂is then prepared by methods

analogous to those described for the H₂[N₂NH] system.

contain a central amine donor, [(MesNCH₂CH₂)₂NR]^{2- 4}

,

also show significant promise for 1-hexene polymeriza-

tion, although in preliminary studies they are not as

well-behaved as complexes that contain the [(t-Bu-N-

o-C₆H₄)₂O]^2-ligand in terms of living characteristics for

1-hexene polymerization. The [(MesNCH₂CH₂)₂NR]ZrMe₂

systems are of special interest, because [(MesNCH₂CH₂)₂-

NR]ZrMe₂can be activated with MAO in chlorobenzene,

while the attempted activation of [(t-Bu-N-o-C₆H₄)₂O]-

ZrMe₂under similar conditions did not lead to an active

polymerization catalyst.⁴⁷Therefore, we set out to

explore in detail the nature of the species formed upon

activation of [(MesNCH₂CH₂)₂NR]ZrMe₂species (R )

H, Me) with [PhNMe₂H][B(C₆F₅)₄] or [Ph₃C][B(C₆F₅)₄].

Our initial efforts are reported here. Further elaboration

of these initial findings and the use of activated com-

plexes for the polymerization of olefins will be reported

in due course.

Resu lts

Syn t h esis of [N₂NX]Zr (CH ₃)₂([N₂NX]

)

[(MesNCH₂CH₂)₂NX]^2-; X ) H (1a ), CH₃(1b); Mes

) Mesityl). As reported in a preliminary communica-

tion,⁴(MesNHCH₂CH₂)₂NH (H₂[N₂NH]) can be pre-

Addition of 1 equiv of LiCH₃to [N₂NH]Zr(¹³CH₃)₂

followed by ¹³CH₃I yielded [N₂NMe]ZrMe₂, in which two-

thirds of the methyl groups on Zr are ¹³C-labeled, while

the methyl group on the central nitrogen is completely

¹³C-labeled (Scheme 1). This conclusion follows from

observation of two 1:1:1 patterns in the ¹H NMR

spectrum for the two inequivalent zirconium methyl

resonances (J _CH) 114, 114 Hz) and a doublet resonance

for the methyl group on the central nitrogen (J _CH) 136

Hz). We conclude that the two labeled methyl groups

in [N₂NH]Zr(¹³CH₃)₂statistically scramble with the

methyl group in LiCH₃before methane is evolved.

Possible mechanisms for scrambling of the labeled and

unlabeled methyl groups include fast axial/equatorial

exchange within a neutral dimethyl species, methyl

scrambling via a nonspecific Zr/Li methyl exchange, or

methyl scrambling via a “turnstile” mechanism within

pseudooctahedral “{[N₂NH]ZrMe₃}^-”. Although the pre-

cise mechanism of methane formation is not known, it

seems plausible that a [N₂NLi]ZrMe₂species is formed

and that it reacts cleanly with ¹³CH₃I to yield the

observed product. In general, under no circumstances

have we obtained evidence for any reaction at the

central nitrogen atom or at the methyl group on the

central nitrogen in [N₂NMe]ZrMe₂, at least none that

leads to any identifiable change. Therefore, the reso-

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Activation of [(MesNCH₂CH₂)₂NR]ZrMe₂Species

Organometallics, Vol. 19, No. 25, 2000 5327

F igu r e 1. ORTEP drawing of the structure of [N₂NH]-

ZrMe₂(1a ).

Sch em e 1

F igu r e 2. ORTEP drawing of the structure of [N₂NMe]-

ZrMe₂(1b).

trigonal bipyramid with “axial” amido nitrogen atoms

and “equatorial” methyl groups, which we call the mer

form. In both structures the three nitrogen atoms lie in

a plane that approximately bisects the C(1)-Zr-C(2)

angle. The donor amine nitrogen atom is approximately

tetrahedral in each compound (C-N-C ) 109, 109,

and 112° for 1b), although the C_arm-N_donor-C_armangle

in 1a is slightly larger (116.5(7)°) than it is in 1b

(112.3(6)°). The Zr-N_amine, Zr-N_amido, and Zr-Me bond

lengths and C-Zr-C, N-Zr-N, and Zr-N-C bond

angles are all typical of diamido/N_donorcomplexes having

this “mer” geometry.²The two amido nitrogens in 1b

are bent only slightly away from the side of the molecule

that contains C(3), as judged by the difference between

the N(1)-Zr-C(1) and N(1)-Zr-C(2) angles (∼1.3°;

Table 2). The mer geometry in compounds of this type

is clearly shown by the angle between the N(1)-Zr-

N(3) and N(2)-Zr-N(3) planes: 174° in 1a and 178° in

1b. In comparison, the angle between the N(1)-Zr-N(3)

and N(2)-Zr-N(3) planes in a facially coordinated

ligand is only ∼130°. (See below for an example.)

NMR spectra reveal two inequivalent ZrMe groups

with proton resonances at 0.24 and 0.07 ppm in 1a and

0.26 and 0.23 ppm in 1b (C₆D₆, 20 °C). In ¹³C NMR

spectra, the ZrMe resonances are found at 42.45 and

39.63 ppm in 1a and 43.31 and 40.62 ppm in 1b. The

chemical shifts for the methyl groups are somewhat

temperature-dependent, but we cannot say with cer-

tainty on the basis of the chemical shift or temperature

dependence what the conformation is of each species in

solution. In 1b the NMe resonances are found at 2.01

nance for the methyl group on the central nitrogen is a

1

convenient marker and/or internal standard in H and

¹³C NMR studies.

The structures of 1a and 1b are shown in Figures 1

and 2. (See Table 1 for crystallographic details and

Table 2 for selected bond distances and angles.) The

coordination geometry about each Zr is a distorted

5328 Organometallics, Vol. 19, No. 25, 2000

Schrock et al.

Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t Deta ils for [N₂NH]Zr (CH₃)₂(1a ), [N₂NMe]Zr (CH₃)₂(1b),

{[N₂NMe]Zr (CH₃)(Et₂O)}[B(C₆F ₅)₄] (2b), a n d [{[N₂NMe]Zr (CH₃)}₂(µ-CH₃)][B(C₆F ₅)₄] (5b)^a

1a

1b

2b

5b

formula

fw

C

_34.0150H₄₉N₃Zr

C₂₅H₃₉N₃Zr

472.81

C₅₂H₄₆BF₂₀N₃OZr

1210.95

C₇₃H₇₅BF₂₀N₆Zr₂

1609.66

596.99

cryst size (mm)

space group

0.24 × 0.12 × 0.08

0.12 × 0.12 × 0.12

0.38 × 0.38 × 0.16

0.12 × 0.2 × 0.2

P2₁/c

Pnma

P2₁/n

P2₁/c

a (Å)

b (Å)

c (Å)

18.740(11)

10.874(5)

17.541(7)

90

110.54(4)

90

3347(3)

4

1.185

0.353

13.1319(8)

24.1909(14)

7.9669(5)

90

2530.9(3)

4

1.241

0.449

1000

17.7775(3)

12.4765(2)

24.3498(5)

90

108.54(1)

90

5120.52(16)

4

1.571

14.268(3)

19.568(6)

25.719(7)

90

93.46(3)

90

7168(3)

4

1.492

0.389

R (deg)

â (deg)

γ (deg)

V (Å³)

Z

calcd density (g/cm³)

µ (mm^-1

F(000)

T (K)

)

0.330

2448

187(2)

1260

183(2)

3268

183(2)

192(2)

θ range (ω scans) (deg)

2.20-19.99

-20 e h e 18

-12 e k e 19

-14 e l e 19

9623

1.68-23.27

-14 e h e 14

-26 e k e 16

-8 e l e 8

9642

2.06-20.00

-16 e h e 17

-11 e k e 12

-20 e l e 23

14 652

2.20-20.00

-7 e h e 12

-14 e k e 18

-22 e l e 24

9897

index ranges

no. of rflns collected

no. of indep rflns

3122

1868

4753

6209

no. of data/restr/params

goodness of fit on F²

R1/wR2 (I > 2σ(I))

R1/wR2 (all data)

extinction coeff

2977/0/353

1.118

0.0692/0.1565

0.0945/0.1759

0.0031(5)

0.577/-0.354

1868/0/140

1.113

0.0526/0.1244

0.0788/0.1401

0.0000(7)

0.432/-0.401

4753/0/704

1.343

0.0663/0.1184

0.0736/0.1205

0.00040(10)

0.359/-0.340

6209/0/919

0.907

0.0532/0.0945

0.1350/0.1173

0.0000(9)

0.461/-0.333

max/min peaks (e/Å³)

a

b

All structures were solved on a Bruker CCD diffractometer using 0.710 73 Å Mo KR radiation. R1 ) ∑||F_o| - |F_c||/∑|F_o|. ^cwR2 )

[(∑w(|F_o| - |F_c|)²/∑wF_o²)]^1/2

.

Ta ble 2. Bon d Len gth s (Å) a n d An gles (d eg) for

[N₂NH]Zr Me₂(1a ) a n d [N₂NMe]Zr Me₂(1b)

1a

1b

Zr-N(1)

2.095(6)

2.248(9)

2.255(9)

2.387(7)

2.095(4)

2.240(7)

2.265(7)

2.373(5)

Zr-N(2)

Zr-C(1)

Zr-C(2)

Zr-N(3)

N(1)-Zr-N(2)

N(1)-Zr-C(1)

N(1)-Zr-C(2)

N(1)-Zr-N(3)

N(2)-Zr-C(2)

N(2)-Zr-N(3)

N(2)-Zr-C(1)

C(1)-Zr-C(2)

C(1)-Zr-N(3)

C(2)-Zr-N(3)

Zr-N(1)-C(11)

Zr-N(2)-C(21)

N(1),Zr,N(3)/N(2),Zr,N(3)

C-N-C

140.0(3)

140.5(2)

102.1(3)

102.3(3)

70.1(2)

103.4(3)

70.3(2)

101.8(3)

102.3(3)

135.1(3)

122.6(3)

121.8(5)

120.4(5)

174^a

101.46(13)

102.78(13)

70.26(11)

102.78(13)

70.26(11)

101.46(13)

103.2(3)

129.2(2)

127.6(3)

118.8(3)

178^a

116.5(7)

112.3(6)

a

Obtained from a Chem 3D model.

F igu r e 3. Peak intensities versus time for labeled methyl

groups, as determined by ¹³C NMR spectroscopy in C₆D₆,

in a mixture of *1a ([[N₂NH]Zr*Me₂) and 1b ([N₂NMe]-

ZrMe₂): (b) *1a (eq); (O) *1a (ax); (9 *1b(eq); (0) *1b(ax).

[*1a ]₀) 5.41 mM; [1b]₀) 74.3 mM. The intensities of *1b

resonances have been corrected for the initial concentration

of naturally abundant ¹³C using the unlabeled NMe sub-

stituent as an internal standard.

ppm in the ¹H NMR spectrum and 37.10 ppm in the

¹³C NMR spectrum.

Addition of [N₂NMe]ZrMe₂(1b; 74.3 mM) to [N₂NH]-

Zr*Me₂(*1a ; 5.41 mM) led to a scrambling of the ¹³C-

labeled methyl groups in 1a with the unlabeled groups

(naturally abundant ¹³C) in 1b over a period of several

hours. (The excess of 1b ensures that >95% of the

labeled methyl groups end up in 1b and that labeled

methyl groups disappear from *1a in a pseudo-first-

order manner.) As shown in Figure 3, the labeled methyl

groups in *1a scramble into 1b completely in ∼7 h, but

at that point the amount of labeled methyl group in the

equatorial methyl position in *1b is 5.5 times the

amount in the axial methyl position; i.e., a labeled

methyl group scrambles from 1a into 1b specifically into

an equatorial position, and axial/equatorial scrambling

within partially and selectively labeled 1b is relatively

slow. (Assignment of the Zr-Me resonances is based

upon 2D NMR studies, as described in the Experimental

Section.) Note that both axial and equatorial labeled

methyl groups disappear from *1a at approximately the

same rate. The rate constant for the intermolecular

methyl scrambling process from the data shown in

Activation of [(MesNCH₂CH₂)₂NR]ZrMe₂Species

Organometallics, Vol. 19, No. 25, 2000 5329

Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles

(d eg) in {[N₂N(CH₃)]Zr (CH₃)(Et₂O)}[B(C₆F ₅)₄]

Sch em e 2

Bond Lengths

Zr(1)-C(1)

Zr(1)-O(1)

Zr(1)-N(3)

2.391(8)

2.234(5)

2.049(6)

Zr(1)-N(1)

Zr(1)-N(2)

2.014(7)

2.426(6)

Bond Angles

87.3(2) N(1)-Zr(1)-N(2)

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

70.1(2)

O(1)-Zr(1)-N(2) 170.5(2) N(3)-Zr(1)-C(1)

114.0(2)

99.9(2)

119.9(3)

72.5(2)

O(1)-Zr(1)-C(1)

90.7(2) N(3)-Zr(1)-O(1)

N(1)-Zr(1)-C(1) 109.5(3) N(3)-Zr(1)-N(1)

N(1)-Zr(1)-O(1) 119.3(2) N(3)-Zr(1)-N(2)

N(1),Zr,N(2)/

N(2),Zr,N(3)

132^a

Zr(1)-N(1)-C(16)-C(21) 88.9(7)

Zr(1)-N(3)-C(16)-C(17) 101.7(8)

a

Obtained from a Chem 3D model.

Syn th esis a n d Id en tifica tion of Ca tion s Th a t

Con ta in Dieth yl Eth er or Dim eth yla n ilin e. The

reaction of 1a or 1b with 1 equiv of [Ph₃C][B(C₆F₅)₄] in

chlorobenzene at -20 °C, followed by the addition of

diethyl ether, led to compounds formulated as {[N₂NX]-

Zr(CH₃)(ether)}[B(C₆F₅)₄] (X ) H (2a ), Me (2b); eq 2).

These products were isolated as yellow powders in 80%

(2a ) and 90% (2b) yields upon addition of pentane.

Figure 3 (60-330 min) is [8.2(4)] × 10^-2M^-1min^-1

,

while the first-order rate of axial/equatorial scrambling

in 1b (between t ) 500 and 830 min) is [5.1(2)] × 10^-4

min^-1. A plausible mechanism (Scheme 2) consists of

formation of a dimeric species that contains a fac form

of the ligand and equivalent bridging methyl groups

trans to the amido ligands and pseudooctahedral coor-

dination geometries around each Zr. This process

would generate initially the [N₂NMe]Zr*Me_eqMe_axform

of *1b. Intramolecular scrambling of *Me and Me within

[N₂NMe]Zr*Me_eqMe_axto give [N₂NMe]ZrMe_eq*Me_axthen

could be accomplished via (for example) a pseudorota-

tion process. Although it is not necessary to dissociate

and invert the amine donor in order to scramble “axial”

and “equatorial” methyl groups in a fac structure (or,

alternatively, a methyl group syn with respect to the

amine substituent with that anti with respect to the

amine substituent in a mer structure), we cannot

discount that possibility. However, we do not favor this

option in view of the relatively electrophilic nature of

zirconium. There is more than one possible reason axial

and equatorial labeled methyl groups in 1a both dis-

appear at the same rate, the simplest being that axial/

equatorial scrambling in 1a is relatively fast, in contrast

to 1b. (As noted above, rapid axial/equatorial scrambling

in 1a could be responsible for the result shown in

Scheme 1.) After considering a variety of potentially

complicating mechanistic features of this scrambling

process, and with the knowledge that alkyls scramble

in other diamido/donor systems that we have been

studying,^47,52we have decided to revisit this process at

a later date. One of the several interesting questions

that at least should be stated in view of our focus in

this paper on cationic (see below) and anionic (trimethyl)

diamido/donor Zr complexes is whether methyl group

exchange between Zr centers might be “ionic” rather

than covalent: e.g., involve formation of a Zr⁺Zr^-pair.

Single crystals of 2b suitable for X-ray diffraction

were grown from pentane/chlorobenzene at -28 °C (see

Tables 1 and 3). Compound 2b⁺(signifying the cation

only) has a distorted-trigonal-bipyramidal structure in

which the [N₂NMe]^2-ligand is coordinated facially, the

Zr-Me group (C(1)) is equatorial, and the diethyl ether

is in an axial position (Figure 4), as shown by the N(1)-

Zr-N(3) angle of 119.9(3)° and the O(1)-Zr-N(2) angle

of 170.5(2)°. The sum of the angles at the oxygen is

358.0°, which indicates that it is close to being trigonal

planar. Perhaps the most accurate measure of the

nature of the ligand’s coordination geometry is the angle

between the N(1)-Zr-N(2) and N(3)-Zr-N(2) planes

(132°), which is markedly reduced from what it is in 1a

(174°) and 1b (178°) and is typical of a complex that

has the “fac” structure, e.g., [(t-Bu-N-o-C₆H₄)₂O]ZrMe₂.²

The Zr(1)-C(1) distance (2.391(8) Å) is approximately

0.1 Å longer than what it is in 1a and 1b. The N(3)-

Zr(1)-N(1) angle (119.9(3)°) is the largest of the three

N-Zr-N angles. The N_amido-Zr bond lengths (Zr(1)-

N(1) ) 2.014(7) Å, Zr(1)-N(3) ) 2.049(6) Å) are similar

to those in 1a and 1b, but the Zr(1)-N(2) distance

(2.426(6) Å) is somewhat longer than a typical Zr-N_donor

distance (∼2.30 Å). The structure of the [B(C₆F₅)₄]^-

anion is normal.

(52) Mehrkhodavandi, P. Unpublished observations.

5330 Organometallics, Vol. 19, No. 25, 2000

Schrock et al.

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

solution of 1b in chlorobenzene yielded {[N₂NMe]Zr-

(CH₃)(NMe₂Ph)}[B(C₆F₅)₄] (3b; eq 3) quantitatively.

Compound 3b could be isolated in 95% yield as a orange

powder by addition of pentane to the chlorobenzene

solution. NMR spectra of 3b in C₆D₅Br between -10

and 60 °C are shown in Figure 5. All resonances

were assigned on the basis of NOE experiments (e.g.,

see eq 4) and comparison with spectra of the analogous

compound prepared from [N₂N*Me]Zr^#Me₂(# implies

67% ¹³C).

F igu r e 4. Views of [N₂NMe]Zr(CH₃)(ether)}⁺(2b): (top)

ORTEP diagram; (bottom) Chem 3D view down the

O-Zr-N axis.

The VT NMR spectra (¹H and ¹³C; -25 to 60 °C) of

2a and 2b in C₆D₅Br are consistent with the structure

of 2b⁺in the solid state. For example, the ¹³C{¹H} NMR

spectrum of 2b (recorded for the Zr(¹³CH₃) complex)

showed sharp resonances for the CH₃N (45.7 ppm) and

CH₃Zr (39.8 ppm) groups (cf. 36.8 ppm for the NMe

group and 42.5 and 39.9 ppm for the ZrMe groups in

1b). In a 1:4 mixture of C₆D₅Br and C₆D₅CD₃the Zr-

CH₃resonance is observed at 39.5 ppm at 22 °C and

shifts to 38.5 ppm at -50 °C before the product crystal-

lizes out of solution. The bound diethyl ether in 2b does

not exchange with free ether on the NMR time scale,

as shown in spectra of samples to which ether has been

added. The bound ether appears to freely rotate about

the Zr-O bond on the NMR time scale, as evidenced by

the overall mirror symmetry and equivalence of the four

methylene protons. Rotation of the mesityl rings around

the N-C_ipsobond is slow on the NMR time scale on the

basis of the observation of inequivalent o-methyl groups

and inequivalent aryl ring protons in a given mesityl

group. A ¹H NMR NOEDIF experiment for complex 2b

at room temperature revealed a NOE (+1.4%) between

the NCH₃(2.38 ppm) and the ZrCH₃(0.19 ppm) protons,

consistent with the equatorial methyl ligand’s proximity

At 20 °C several resonances are broad, including that

ascribed to ZrCH₃at 0.07 ppm. At 60 °C all resonances

are sharp and the spectrum is characteristic of a

structure with C_ssymmetry and nonrotating mesityl

groups. At -10 °C only the resonance that can be

1

ascribed to the mesityl p-methyl groups is sharp. H

NOEDIF experiments show that the dimethylaniline is

bound in the apical pocket and is freely rotating about

the Zr-N bond axis on the NMR time scale at 60 °C. In

an analogous sample in which free NMe₂Ph had been

added, resonances for the ortho aryl protons of both

the coordinated dimethylaniline (5.67 ppm) and free

dimethylaniline (6.80 ppm) were observed. This finding

suggests that the rate of exchange between free and

coordinated dimethylaniline is relatively slow (<∼0.1

s^-1) at 20 °C, while the rate of intramolecular motion

responsible for the fluxional process that leads to broad

resonances near room temperature must be on the order

of ∼10²s^-1. The ¹³C{¹H} NMR spectrum at 20 °C of a

sample prepared from [N₂N*Me]Zr^#Me₂revealed a

sharp resonance for the NCH₃group (at 46.41 ppm) and

a broad resonance for ZrCH₃(at 37.0 ppm). The ¹⁹F

NMR spectrum of 3b at 20 °C showed resonances

characteristic of “free” [B(C₆F₅)₄]^-.

1

to the axial NCH₃group. All other H NMR resonances

were assigned on the basis of similar NOE experiments.

¹⁹F NMR spectra at -25 °C showed resonances for

[B(C₆F₅)₄]^-that are characteristic of an “uncoordinated”

isotropic anion. Complexes 2a and 2b were stable in

C₆D₅Br for several days at room temperature.

Activation of [(MesNCH₂CH₂)₂NR]ZrMe₂Species

Organometallics, Vol. 19, No. 25, 2000 5331

1

F igu r e 5. Variable-temperature H NMR spectra (500 MHz, C₆D₅Br) of {[N₂N(CH₃)Zr](CH₃)(NMe₂Ph)}[B(C₆F₅)₄].

One possible explanation for broadening of most

resonances at low temperatures is that the dimethyl-

aniline adopts one of two different orientations within

the coordination pocket due to a “cog-wheel” effect

between it and the amido mesityl and axial amine

methyl groups. The two possible orientations are shown

in eq 4. The one in which the methyl group is located

between the two mesityl rings would give rise to a

molecule with no symmetry when rotation of the di-

methylaniline in the pocket is slow. At 60 °C rapid

rotation about the Zr-dimethylaniline bond would lead

to a molecule with mirror symmetry on the NMR time

scale. A variation of this explanation is that in the

lowest energy species the ligand backbone is twisted

with C(13) (Figure 4) lying on one side of the plane that

contains C(13), Zr, and N(2), as found in the solid state.

With such a backbone configuration the molecule would

have no symmetry. In this case dimethylaniline could

adopt either coordination mode, since the asymmetry

would arise from the twist in the ligand backbone alone.

Interconversion of “twisted” forms would also be part

of the fluxional process that leads to overall mirror

symmetry at higher temperatures. A preferred twist and

a fluxional process based on interconversion of “twisted”

forms have also been observed in related molecules that

contain the [(t-Bu-N-o-C₆H₄)₂O]^2-ion.²Finally, associa-

tion of the anion at more than one point on any five-

coordinate cation in principle could lead to different

forms being observed at some low temperature, a type

of phenomenon that we believe to be the case in

pseudotetrahedral “{[N₂NMe]Zr(CH₃)}[B(C₆F₅)₄]” (see

below). However, the anion is unlikely to associate

nearly as strongly with a five-coordinate species as with

a four-coordinate or weakly solvated species; therefore,

we do not propose that this behavior is part of the

temperature-dependent process shown in Figure 5.

Addition of diethyl ether to NMR samples of 3b

immediately yields 2b, although addition of dimethyl-

aniline to NMR samples of 2b does not lead to the

formation of any detectable 3b, consistent with a

preferred binding of diethyl ether to the cationic zir-

conium center. Since 3b⁺is almost certainly sterically

too crowded to react readily with another base in an

associative manner, we suggest that dimethylaniline

first dissociates from 3b⁺to yield a “base free” cation

and that diethyl ether then binds in place of dimethyl-

aniline.

When 1b was treated with a slight excess of [PhN-

Me₂H][B(C₆F₅)₄], the initial product was 3b, according

to NMR data. However, 3b rapidly decomposed to yield

methane and a new cationic zirconium complex that

contained no ZrMe group. We propose that this new

species is the product of C-H bond activation in the

1

mesityl’s o-methyl group (eq 5). The H NMR spectrum

of 4b⁺showed two doublets at 2.39 and 0.79 ppm (J _HH

) 12.5 Hz) that can be assigned to the two inequivalent

1

benzylic protons. Their coupling was confirmed in a H

gCOSY experiment. The remaining resonances have

1

been assigned on the basis of H ROESY and H-¹³C

HMQC experiments (see the Experimental Section). We

have observed and obtained structural confirmation that

a “base-free” CH activated version is formed upon

decomposition of {[N₂NMe]ZrMe}[B(C₆F₅)₄] (6b; see

below)⁴⁷and {[N₂NMe]Zr(CH₂CMe₃)}[B(C₆F₅)₄].⁵³These

results will be presented elsewhere. On the basis of this

(53) Schrodi, Y.; Bonitatebus, P. J ., J r. Unpublished observations.

5332 Organometallics, Vol. 19, No. 25, 2000

Schrock et al.

structure, which is a dimeric dication with the activated

mesityl rings behaving as η⁶-arenes toward cationic Zr

centers, an alternative possible structure for 4b⁺con-

tains dimethylaniline in the “apical” position and the

benzylic methylene group in the “equatorial” position

(eq 5). Compound 4b has not yet been isolated in pure

form. Only mixtures of 4b and 3b could be obtained by

addition of pentane to a chlorobenzene solution.

Compound 4b also could be obtained by decomposition

of complex 3b in chlorobenzene (4 h at 60 °C). The

1

decomposition was monitored by H NMR at 60 °C in

C₆D₅Br to ∼68% conversion (using a 21 mM sample).

The reaction followed first-order kinetics with k_decomp

)

[7.68(0.12)] × 10^-3min^-1. Decomposition is clearly much

more rapid in the presence of [PhNMe₂H][B(C₆F₅)₄], as

described above.

Rea ction s of [N₂NX]Zr Me₂(X ) H, CH₃) w ith 0.5

Equ iv of Tr ityl. The reaction between [N₂NMe]ZrMe₂

and 0.5 equiv of [Ph₃C][B(C₆F₅)₄] in chlorobenzene at

-30 °C gave a pale yellow solution. NMR studies were

consistent with the presence of a dimeric monocation,

[{[N₂NMe]Zr(CH₃)}₂(µ-CH₃)][B(C₆F₅)₄] (5b; eq 6). Upon

F igu r e 6. ORTEP drawing of the cation in complex 5b.

Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles

(d eg) in [{[N₂N(CH₃)]Zr (CH₃)]Zr (CH₃)}₂[µ-(CH₃)]⁺

Bond Lengths

Zr(1)-C(1)

Zr(1)-C(2)

Zr(1)-N(1)

Zr(1)-N(2)

Zr(1)-N(3)

2.508(9)

2.229(9)

2.024(8)

2.006(8)

2.433(8)

Zr(2)-C(1)

Zr(2)-C(26)

Zr(2)-N(4)

Zr(2)-N(5)

Zr(2)-N(6)

2.457(9)

2.256(9)

2.049(8)

2.015(8)

2.455(8)

Bond Angles

97.2(3)

92.4(4)

94.8(3)

C(2)-Zr(1)-C(1)

C(2)-Zr(1)-N(3)

C(26)-Zr(2)-C(1)

C(26)-Zr(2)-N(6)

N(1)-Zr(1)-C(1)

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

N(1)-Zr(1)-N(3)

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

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

N(2)-Zr(1)-N(1)

N(6)-Zr(2)-C(1)

Zr(2)-C(1)-Zr(1)

N(2)-Zr(1)-N(3)

N(3)-Zr(1)-C(1)

N(4)-Zr(2)-C(1)

N(4)-Zr(2)-N(26)

N(4)-Zr(2)-N(6)

N(5)-Zr(2)-C(1)

N(5)-Zr(2)-C(26)

N(5)-Zr(2)-N(4)

N(5)-Zr(2)-N(6)

167.4(4)

71.9(3)

170.1(3)

113.2(4)

112.3(4)

71.6(4)

103.9(3)

109.3(3)

120.2(4)

70.9(3)

85.4(4)

102.7(3)

113.1(3)

71.0(3)

107.2(3)

108.3(3)

124.5(3)

174.5(4)

addition of pentane, 5b was isolated as a off-white

powder in 87% yield. Unreacted [N₂NMe]ZrMe₂was

found when the reaction was carried out with less than

0.5 equiv of [Ph₃C][B(C₆F₅)₄], while addition of 0.5-1.0

equiv of [Ph₃C][B(C₆F₅)₄] to 1b yielded mixtures of 5b

and {[N₂NMe]ZrMe}[B(C₆F₅)₄] (6b) (see below).

bond lengths to the apical donor nitrogens (2.457(9) and

2.455(8) Å) are slightly longer (∼0.04 Å) than in

compound 2b⁺, while the Zr-N-C_ipsoangles are similar

to those in 2b⁺and 1b.

Single crystals of 5b suitable for X-ray diffraction

were grown from a mixture of toluene and chloroben-

zene at -28 °C. The solid-state structure of 5b⁺can be

described as an adduct of {[N₂NMe]ZrMe}⁺in which

[N₂NMe]ZrMe₂is the “base” that binds in an apical

position (Figure 6; Tables 1 and 4). The bridging methyl

group is approximately symmetrically bound between

the two zirconium centers (2.508(9) and 2.457(9) Å), and

a C₂axis (not crystallographically imposed) that relates

the two ends of the molecule passes through it. The

[B(C₆F₅)₄]^-anion is closer to one of the Zr centers than

to the other in the crystal lattice. The Zr-C-Zr angle

is close to linear (167.4(4)°). The hydrogen atoms on the

central bridging methyl could not be located in the

difference map. The Zr-C bond lengths to the terminal

(equatorial) methyl groups (2.229(9) and 2.256(9) Å) are

similar to the Zr-C bond lengths found in 1a , 1b, and

2b⁺. The two ends of 5b⁺are staggered with respect to

one another (∼60°), as a consequence of the steric bulk

and interlocking nature of the mesityl groups. The Zr-N

NMR studies in C₆D₅Br suggest that 5b⁺has a

structure in solution that is similar to that found in the

solid state. At -25 °C two sharp resonances are ob-

served that correspond to the terminal (-0.38 ppm) and

bridging (-0.89 ppm) ZrCH₃groups, the former with

twice the intensity of the latter. The average value of

the ¹J _CHcoupling constants in the bridging ZrCH₃group

is 133 Hz, which is consistent with C-H bonds that

have a higher s character and which is significantly

higher than for the terminal ZrCH₃groups (115 Hz).

As a consequence of the “interlocking” nature of the two

ends of 5b⁺, more than four proton resonances are

observed for the methylene protons in the two arms of

the [N₂NMe]^2-ligand and six inequivalent mesityl

methyl groups are observed at -25 °C (Figure 7). The

¹³C{¹H} NMR spectrum at -25 °C, recorded using ¹³C-

labeled 5b⁺, showed resonances for NCH₃(45.02 ppm),

terminal ZrCH₃(41.23 ppm), and µ-CH₃(40.11 ppm)

groups as sharp singlets. These resonances were as-

1

signed on the basis of H-¹³C HMQC experiments.

Activation of [(MesNCH₂CH₂)₂NR]ZrMe₂Species

Organometallics, Vol. 19, No. 25, 2000 5333

1

F igu r e 7. Variable-temperature H NMR spectra (500 MHz, C₆D₅Br) of [{[N₂N(CH₃)Zr](CH₃)}₂(µ-CH₃)][B(C₆F₅)₄].

¹H ROESY experiments at -25 °C were consistent

with the configuration at each metal in the solid state.

The most relevant NOE (negative) cross-peak was the

one between the terminal ZrCH₃and the NCH₃reso-

nances. No cross-peaks were found between the bridging

ZrCH₃and the NCH₃resonances. This result is consis-

tent with the fact that the terminal ZrCH₃groups

occupy equatorial positions and the bridge is formed by

a shared apical ZrCH₃group. NOE cross-peaks were

observed between one set of o-CH₃groups of the mesityl

substituents and the terminal ZrCH₃group. NOE cross-

peaks also were observed between the other set of o-CH₃

groups (the “inside” set at one metal center) with the

another readily. Therefore, we propose a process in

which the two terminal methyl groups are pushed into

bridging positions as the molecule “folds up” using the

bridging methyl group as a “hinge” (eq 7). The transi-

1

bridging ZrCH₃resonance. The H ROESY experiment

at -25 °C also showed EXSY (positive) cross-peaks

between resonances for inequivalent mesityl groups.

This was especially clear in the case of one o-CH₃group

(at ∼1.6 ppm) and indicates that the two inequivalent

mesityl groups are exchanging.

A variable-temperature ¹H NMR study (Figure 7)

revealed that at 55 °C each metal has mirror symmetry

on the NMR time scale. This process cannot consist of

reversible loss of [N₂NMe]ZrMe₂from 5b⁺, since sepa-

rate resonances for [N₂NMe]ZrMe₂and 5b⁺are observed

at 50 °C in a sample of 5b⁺to which [N₂NMe]ZrMe₂has

been added. The resonance for one ortho mesityl methyl

set (at ∼1.55 ppm) is somewhat broader than the other

at this temperature, but it is clear that rotation about

the Mes-N bonds is still slow on the NMR time scale.

The fluxional process does not affect the ZrCH₃and

tion-state structure is then a dinuclear species that has

three bent methyl bridges between two six-coordinate

Zr atoms (two face-sharing pseudooctahedra), in which

a mirror plane passes through Me_band the NMe groups.

Note that the bridging methyl group does not exchange

with a terminal methyl group in this proposed mecha-

nism, which is consistent with what is observed experi-

mentally. The pseudooctahedral structure about each

Zr in the dimeric species shown in eq 7 is reminiscent

of pseudooctahedral fac species proposed in other methyl

exchange reactions (Schemes 1 and 2).

1

NCH₃resonances, which are sharp singlets in both H

and ¹³C{¹H} NMR spectra between -25 and 65 °C. (The

NCH₃and o-CH₃resonances are coincident at 55 °C in

Figure 7.) The rate of this fluxional process was mea-

sured by line shape analysis of the two o-CH₃reso-

nances near 1.5 and 1.6 ppm between 248 and 330 K.

An Eyring plot yielded ∆H^q) 12.5(3) kcal mol^-1and

∆S^q) -3.4(1.2) cal mol^-1K^-1. A process that consists

of pure rotation of the two ends of the dimer with respect

to one another seems improbable on steric grounds, as

the mesityl rings would appear to be unable to pass one

1

In a H ROESY experiment at 45 °C, EXSY (positive)

cross-peaks were observed between the resonances for

the terminal and bridging methyl groups and between

the resonances for the two inequivalent o-CH₃groups

5334 Organometallics, Vol. 19, No. 25, 2000

Schrock et al.

in the mesityl groups, which suggests that terminal and

bridging methyl groups are exchanging on the chemical

time scale at this temperature, as are the two mesityl

o-methyl groups. Bridging and terminal methyl groups

exchange at rates on the order of ∼10^-1s^-1(at 45 °C),

whereas at 45 °C the rate of intermetallic exchange of

terminal methyl groups is approximately 4000 s^-1. At

25 °C the ROESY spectrum shows no EXSY (positive)

cross-peaks that would signal exchange of terminal and

bridging methyl groups.

Addition of 1 equiv of [Ph₃C][B(C₆F₅)₄] to ¹³C-labeled

1a in C₆D₅Br followed by addition of 1 equiv of 1b

yielded a statistical mixture of 5a , 5b, and [{[N₂NMe]-

Zr(CH₃)}(µ-CH₃){[N₂NH]Zr(CH₃)}][B(C₆F₅)₄] in which

the ¹³C label was scrambled throughout the ZrMe

positions. These data suggest that intra- and inter-

molecular scrambling processes discussed above for 1b

and 5b are also found in 1a and 5a . For example,

formation of [{[N₂NMe]Zr(CH₃)}(µ-CH₃){[N₂NH]Zr-

(CH₃)}][B(C₆F₅)₄], in which the ¹³C label is completely

scrambled between the bridging and terminal positions,

suggests that dissociation of any neutral dimethyl-

zirconium complex from “{[N₂NX]Zr(CH₃)}⁺” (X ) H,

Me) is fast on the chemical time scale (seconds).

Since 5b⁺is essentially a [N₂NMe]ZrMe₂adduct of

“{[N₂NMe]ZrMe}⁺”, we might suspect that [N₂NMe]-

ZrMe₂is lost readily from [{[N₂NMe]ZrMe}₂(µ-Me)]⁺

on the chemical time scale. This was confirmed by

1

observing H and ¹³C{¹H} NMR spectra of a mixture of

Rea ction s of [N₂NX]Zr (CH₃)₂(X ) H, CH₃) w ith

1 Equ iv or Mor e of [P h ₃C][B(C₆F ₅)₄]. The reaction

between [N₂NMe]Zr(CH₃)₂and 1 equiv of [Ph₃C]-

[B(C₆F₅)₄] in C₆D₅Br at -30 °C produces a yellow solu-

[N₂NMe]Zr*Me₂and 5b (1:2 ratio) in C₆D₅Br at 22 °C

10 min after mixing. By this time the Zr-methyl groups

in [N₂NMe]Zr*Me₂had scrambled with the unlabeled

Zr-methyl groups in 5b to produce a mixture in which

*Me was present statistically in all Zr-methyl positions

in all species. Therefore, the process shown in eq 8 must

1

tion. The H NMR spectrum of this solution at 20 °C

revealed that Ph₃CCH₃had formed quantitatively, along

with a species having a methyl resonance at 0.15 ppm,

consistent with formation of {[N₂NMe]Zr(CH₃)}[B(C₆F₅)₄]

(6b). As a sample of 6b is cooled to -35 °C, the methyl

resonance broadens and a resonance begins to grow in

near -0.02 ppm and to increase in intensity; the

resonances for what we shall call 6b₁(near 0.15 ppm)

and 6b₂(near -0.02 ppm) sharpen at lower tempera-

tures (Figure 8a). The ratio of the two resonances at

-35 °C is close to 1:1. This behavior is repeatable and

reversible. (For the moment we will ignore the small

peak at -0.15 ppm, although it also appears to be a part

of this temperature-dependent process.) The proportion

of 6b₂in the 6b₁/6b₂mixture decreases as the temper-

ature is increased (Figure 8a), and 6b₁begins to

interconvert with 6b₂. The equilibrium constant, K_eq

)

[6b₁]/[6b₂], was measured between 254 and 273 K at a

concentration of 22 mM. Values of ∆H° ) 7.9(5) kcal

mol^-1and ∆S° ) 32(3) cal mol^-1K^-1were obtained from

a van’t Hoff plot. Upon dilution of the sample (from

[Zr] ) 53 to 26 mM), isomer 6b₂was the dominant

species at low temperatures. Interconversion of 6b₁and

6b₂between -35 and 20 °C was modeled by line shape

analysis (Figure 8b), taking into account the observed

change in the amount of 6b₁and 6b₂at various temper-

atures, as calculated from the temperature dependence

of K close to and above the coalescence point. An Eyring

plot (248-293 K) led to values of ∆H^q) 16.3(5) kcal

mol^-1and ∆S^q) 8(2) cal mol^-1K^-1for the conversion

of 6b₂to 6b₁.

be rapid at 22 °C relative to the rate of exchange of

equatorial and axial methyl groups in [N₂N*Me]Zr*Me₂

and bridging and terminal methyl groups in 5b. The

fact that 5b is readily isolated suggests that the equi-

librium constant for the dissociation shown in eq 8

probably is relatively small. We know that 5b reacts

with 1 equiv of trityl readily to give “{[N₂NMe]ZrMe}⁺”

(see below) but do not know whether it does so in a

direct way or as a result of the dissociation shown in eq

8: i.e., via [N₂NMe]ZrMe₂.

The two new species, 6b₁and 6b₂, have mirror

symmetry on the NMR time scale and appear be two

isomers of “{[N₂NMe]Zr(CH₃)}[B(C₆F₅)₄]”. The ¹⁹F NMR

spectrum of the mixture at -25 °C showed resonances

consistent with “uncoordinated” [B(C₆F₅)₄]^-at chemical

shifts that are virtually identical with those found

in other ionic compounds reported here. Complex 6b

was stable in C₆D₅Br solution at -25 °C for days, but

it decomposed at room temperature after 60 min,

producing methane at the expense of the ZrCH₃group.

Preliminary results⁴⁷to be reported in full elsewhere

confirm that this product is a solvent-free dimer of 4b⁺.

Compound 5b is surprisingly stable in C₆D₅Br solu-

tion. Some decomposition was observed after 5 min at

65 °C or after 1 day at 20 °C. Formation of methane

could be confirmed, but the decomposition product or

products could not be identified. Addition of 0.5 equiv

of [Ph₃C][B(C₆F₅)₄] to 1a in C₆D₅Br yielded a species

analogous to 5b, namely [{[N₂NH]Zr(CH₃)}₂(µ-CH₃)]-

[B(C₆F₅)₄] (5a ), according to NMR spectra. Two zirco-

1

nium methyl resonances are found in both H and ¹³C

1

NMR spectra in a 2:1 ratio. A H ROESY experiment

at -10 °C showed negative (NOE) cross-peaks for the

terminal and bridging methyl groups; i.e., the two are

not exchanging readily at this temperature. All NMR

data suggest that the structure of 5a is similar to that

of 5b.

The reaction between [N₂N(*CH₃)]Zr(^#CH₃)₂and [Ph₃C]-

[B(C₆F₅)₄] yielded the same isotopic distribution of ¹²C

and ¹³C in the NMe and ZrMe groups in 6b₁and 6b₂

Activation of [(MesNCH₂CH₂)₂NR]ZrMe₂Species

Organometallics, Vol. 19, No. 25, 2000 5335

1

F igu r e 8. (a, top) Variable-temperature H NMR spectra (500 MHz, C₆D₅Br) of the ZrCH₃resonances in a mixture of 6b₁

and 6b₂. (b, bottom) Computer simulation and first-order rate constants (k_1,2) in s^-1

.

5336 Organometallics, Vol. 19, No. 25, 2000

Schrock et al.

(and triphenylethane) as in [N₂N(*CH₃)]Zr(^#CH₃)₂; i.e.,

the products appeared to be “{[N₂N(*CH₃)]Zr(^#CH₃)}⁺”

and Ph₃C^#CH₃(# implies 67% ¹³C; * implies 100% ¹³C).

The ¹³C{¹H} NMR spectrum of “{[N₂N(*CH₃)]Zr(^#CH₃)}⁺”

at -25 °C showed sharp resonances for the NCH₃

groups at 45.47 ppm in 6b₁and 46.51 ppm in 6b₂. Both

resonances are downfield of where they are observed

in [N₂N(*CH₃)]Zr(^#CH₃)₂(35.9 ppm). In 6b₁, the Zr-

Me resonance is found at 47.25 ppm, downfield with

respect to those in [N₂N(*CH₃)]Zr(^#CH₃)₂(40.7 and 42.7

ppm), similar to the chemical shift for an equatorial

methyl group in 2b and 3b. However, the Zr-Me

resonance in 6b₂appeared at 33.52 ppm, which is a

significantly higher field position than found for the

ZrMe group in 6b₁.

structure of 6a ₂⁺is similar to that of 6b₁⁺and 6b₂⁺and

other monomeric ionic species discussed here (2b⁺and

3b⁺).

A solution that contains a mixture of complexes 6a

and 6b was investigated via a ¹H ROESY experiment

at -25 °C. For this purpose, a sample was prepared by

mixing two freshly prepared solutions (∼53 mM) of each

in C₆D₅Br. A chemical interconversion of 6b₁and 6b₂

was indicated (EXSY cross-peaks for the ZrMe groups),

but not between 6a ₂and 6b₁or 6a ₂and 6b₂. Another

experiment was carried out in which Zr(*Me)-labeled

6a was mixed with unlabeled 6b; no incorporation of

the ¹³C label into 6b was observed. Both experiments

suggest that ZrMe groups do not exchange between 6a

and 6b readily on the chemical time scale.

Similar behavior is observed for the ZrCH₃resonance

by both proton and carbon NMR in a 1:4 mixture of

C₆D₅Br and C₆D₅CD₃. For example, a 10 mM sample

showed resonances only for 6b₂down to -20 °C, where

the ZrCH₃carbon resonance was observed at 32.67 ppm

and the proton resonance at -0.078 ppm. At -30 °C

two carbon resonances were observed at 32.49 and 32.33

ppm and two proton resonances at -0.135 and -0.187

ppm. Below -50 °C these resonances broadened and

decreased in intensity as an oil precipitated from

solution. The precise nature of the two forms of 6b₂

below -30 °C in this mixed solvent is not known.

Discu ssion

The mer structures for 1a and 1b that were found in

the solid state (versus fac structures) were initially

surprising to us. However, the flexibility of the arms

that connect the amine nitrogen with the amido nitro-

gens apparently allows the tetrahedral amine donor to

be accommodated in a mer structure. Orientation of

the plane of the aryl rings perpendicular to the plane

of the amido nitrogen is favored for steric reasons and

was noted initially by McConville in a variety of

titanium and zirconium complexes.^{14-16,18-21,23,24}There

is little steric hindrance between the aryl groups and

the equatorial methyl ligands. Therefore, the structure

has essentially no tendency to “twist” into a fac form.

Steric interaction between the tert-butyl groups and

the methyl groups in a mer structure is thought to be

one of the main reasons why [(t-Bu-N-o-C₆H₄)₂O]ZrMe₂

has a fac structure in the solid state, while [(i-Pr-

N-o-C₆H₄)₂O]ZrMe₂has a mer structure.^2,12In contrast,

the core structures of the two “base adducts” (2b⁺and

5b⁺) are fac with the base (diethyl ether or [N₂NMe]-

ZrMe₂, respectively) bound in an apical position trans

to the amine donor. This is the same type of structure

that is observed for {[(t-Bu-N-o-C₆H₄)₂O]ZrMe}[MeB-

(C₆F₅)₃], in which the “base” is [MeB(C₆F₅)₃]^-.^2,3One

might have predicted in each system that the equatorial

site would have been the least hindered position steri-

cally and that the base would bind there. However, the

top view of 2b shown in Figure 4 emphasizes that

the “outside” o-methyl groups on each mesityl ring

might interact sterically to a significant degree with

whatever ligand is in the equatorial position and that

a methyl group might be the least demanding sterically

in the equatorial position compared to diethyl ether or

[N₂NMe]ZrMe₂. It should be noted that the six-coordi-

nate structure of {[(t-Bu-N-o-C₆H₄)₂O]ZrMe(dimethoxy-

ethane)}⁺is essentially fac, with the methyl group in

the apical position and one of the dme oxygens binding

weakly to an upper CON face,²and that pseudoocta-

hedral {[(t-Bu-N-o-C₆H₄)₂O]ZrMe(THF)₂}⁺contains the

ligand in the mer configuration with the two THF

ligands trans to one another.²

1

On the basis of H ROESY experiments at -35 °C,

+

the structures of 6b₁and 6b₂in solution appear to

be similar to the structures of 2b⁺, 3b⁺, and 5b⁺. The

¹H ROESY spectrum of “{[N₂N(*CH₃)]Zr(^#CH₃)}⁺” shows

intense EXSY (positive) cross-peaks between related

signals of both complexes, which confirms that 6b₁⁺and

+

6b₂are in equilibrium. As we shall elaborate upon in

+

the Discussion, all evidence points toward 6b₁⁺and 6b₂

being two types of {[N₂NMe]Zr(CH₃)}[B(C₆F₅)₄] ion

pairs.

The reaction of [N₂NH]Zr(CH₃)₂with [Ph₃C][B(C₆F₅)₄]

in C₆D₅Br also led to a yellow solution. In this case,

along with the signal corresponding to Ph₃CCH₃, the

¹H NMR spectrum at -25 °C suggested the quantitative

formation of only one major new complex analogous to

6b₂: i.e., 6a ₂(eq 9). Assignment was made on the basis

of the chemical shift of the ZrCH₃resonance at -0.13

1

ppm in the H NMR spectrum and at 31.3 ppm in the

¹³C{¹H} spectrum (recorded using the ¹³C-labeled com-

plex). (We must assume that chemical shifts in the two

species are a reliable indicator of their nature.) At 20

°C only one broad resonance for the Zr-Me group was

observed in both the ¹H (-0.08 ppm) and ¹³C{¹H} (31.70

There is much precedent for the formation of neutral

homometallic M(µ-Me)M species in the literature, where

M is a transition metal, lanthanide, or actinide: e.g.,

Zr(µ-Me)Zr,^54-57Lu(µ-Me)Lu,⁵⁸and U(µ-Me)U species.⁵⁹

1

ppm) NMR spectra. An H ROESY experiment at -25

°C showed a NOE (negative) cross-peak between signals

of the ZrCH₃and NH (2.88 ppm) groups and between

one o-CH₃group in the mesityl substituents with the

ZrCH₃group. According to these studies, the basic

(54) Buchwald, S. L.; Lucas, E. A.; Davis, W. M. J . Am. Chem. Soc.

1989, 111, 397.

Activation of [(MesNCH₂CH₂)₂NR]ZrMe₂Species

Organometallics, Vol. 19, No. 25, 2000 5337

However, more relevant to the formation of 5a ⁺and 5b⁺

are monocationic species that contain a bridging methyl

group: e.g., various [Zr(µ-Me)Zr]⁺species^60-64and a

[Th(µ-Me)Th]⁺species.⁶⁵In all cases the compounds are

derived from metallocenes. Metallocenes and metal-

locene cations have received intense scrutiny in the last

15 years, in particular with respect to cations as

relatively well-defined catalysts for the polymerization

of ethylene and terminal olefins. We believe 5b⁺to be

the first example of a “non-metallocene” monocationic

[M(µ-Me)M]⁺species. Its formation is sensible on the

basis of published metallocene [Zr(µ-Me)Zr]⁺structures,

the ability of methyl groups to bridge in a linear or bent

manner between two of the same or two different metals

(including main-group metals), and the formation of

other cationic species described here that contain a

“base” less exotic than [N₂NMe]ZrMe₂, e.g., diethyl ether

or dimethylaniline. Although we could not locate the

protons on the bridging methyl group in 5b⁺, the

approximately equal Zr-(µ-Me) bond lengths, along

with the large CH coupling constant, suggest that the

methyl group is essentially planar, as found in several

other neutral and monocationic Zr-(µ-Me)Zr species.

One of the most important questions that we must

address here is the nature of 6b₁and 6b₂. We have

considered several explanations and have decided on the

basis of results in the literature, in particular relatively

recent studies by Marks⁶⁶and calculations by Ziegler,⁶⁷

that only one explanation can be argued successfully:

namely, that 6b₁and 6b₂are different ion pairs whose

interconversion at low temperatures is slow enough to

observe on the NMR time scale. (There are three

different faces in an untwisted tetrahedral cation such

as 6b⁺; therefore, three possible ion pairs could be

observed in theory, two of which have mirror symmetry.)

Before we discuss the nature of the ion pairs, we should

outline some of the findings of Marks and Ziegler for

metallocene and constrained-geometry catalysts.

[MeB(C₆F₅)₃]^-ion from one position in the pseudo-

tetrahedral ion pair to the other.^66,68In {(η⁵-1,2-

Me₂C₅H₃)₂ZrMe}[MeB(C₆F₅)₃] in toluene at 298 K the

rate of migration of the B(C₆F₅)₃fragment was found

to be 3 × 10^-3s^-1, while the rate of migration of the

[MeB(C₆F₅)₃]^-ion was found to be 30 × 10^-3s^-1. In

chlorobenzene the rates were found to be 60 and 2.0 ×

10⁴s^-1, respectively. Unfortunately, analogous systems

in which the anion is [B(C₆F₅)₄]^-are unstable. There-

fore, it was not possible to measure the rate of [B(C₆F₅)₄]^-

ion migration and compare it to the rate of [MeB(C₆F₅)₃]^-

ion migration.

A recent paper by Ziegler explores these issues and

others theoretically using DFT calculations for (η⁵-1,2-

Me₂C₅H₃)₂ZrMe₂combined with various Lewis acids,

including {(η⁵-1,2-Me₂C₅H₃)₂ZrMe}[B(C₆F₅)₄] species.⁶⁷

His calculations reproduce the experimental findings of

Marks for species that contain the [MeB(C₆F₅)₃]^-ion.^66,68

Moreover, Ziegler calculates that, upon changing the

solvent from toluene to chlorobenzene, the ion pair

dissociation energy (∆H_ips) for the [MeB(C₆F₅)₃]^-ion

decreases from 38.0 to 23.4 kcal mol^-1, or about 40%,

while upon changing to the [B(C₆F₅)₄]^-ion in toluene,

∆H_ipsdrops to 22.0 kcal mol^-1. No value for ∆H_ips

for the [B(C₆F₅)₄]^-ion in chlorobenzene was provided,

but if ∆H_ipswere to drop from 22.0 kcal mol^-1by 40%,

we would expect ∆H_ipsfor the [B(C₆F₅)₄]^-ion in chloro-

benzene to be ∼13 kcal mol^-1. Ziegler notes that no

zirconium cation/anion pairs are ever likely to be

“completely solvated.” Nevertheless, calculated ∆H_ips

values are a good measure of the degree of cation/anion

interaction in various solvents and, in particular, the

degree to which the anion might bind in a given position

on a pseudotetrahedral cation. All ∆H_ipsvalues will

depend dramatically on the steric crowding in the

cation, the degree to which the negative charge is

delocalized in the anion, the nature of the anion, etc.

To our knowledge there are no experimental results

in the literature which suggest that different ion pairs

in which [B(C₆F₅)₄]^-is the anion can be observed at

low temperatures. It should be noted, however, that

an X-ray structure of {Cp*₂ThMe}[B(C₆F₅)₄] shows

[B(C₆F₅)₄]^-to be associated with the Th through F_ortho

and F_metainteractions in one ring, with the Th-F

distances being longer than the relevant Th⁴⁺and F^-

ionic radii.⁶⁵Interestingly, however, the ¹⁹F NMR

spectrum in toluene-d₈, a solvent in which the anion

might be expected to be more strongly associated with

the cation than in chlorobenzene, showed magnetically

equivalent C₆F₅rings down to -70 °C. This result

suggests that although the association of the {Cp*₂-

ThMe}⁺cation and the [B(C₆F₅)₄]^-anion is strong

enough to isolate a crystalline adduct, the [B(C₆F₅)₄]^-

anion must be “tumbling” rapidly on the NMR time

scale (>100 s^-1) between various types of Th-F interac-

tions and from one C₆F₅ring to the other, etc., even at

-70 °C in toluene. Therefore, ¹⁹F NMR spectra of

[B(C₆F₅)₄]^-salts are unlikely to be reliable predictors

of the degree to which the [B(C₆F₅)₄]^-ion is associated

with the cation. It also seems unlikely that one could

distinguish between association of a [B(C₆F₅)₄]^-ion with

a cation in more than one position, i.e., on more than

There is now a significant amount of evidence that

[MeB(C₆F₅)₃]^-can associate relatively strongly with a

pseudo-three-coordinate metallocene cation. Marks and

his group in particular have experimentally measured

both the rate of migration of the B(C₆F₅)₃fragment from

one methyl group to the other in a neutral metallocene

dimethyl complex and the rate of migration of the

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Organometallics 1990, 9, 2843-2846.

(56) Waymouth, R. M.; Bronikowski, M. J .; Coots, R. J .; Grubbs, R.

H.; Santarsiero, B. D. J . Am. Chem. Soc. 1986, 108, 1427.

(57) Waymouth, R. M.; Santarsiero, B. D.; Grubbs, R. H. J . Am.

Chem. Soc. 1984, 106, 4050.

(58) Watson, P. L.; Parshall, G. W. Acc. Chem. Res. 1985, 18, 51.

(59) Stults, S. D.; Andersen, R. A.; Zalkin, A. J . Am. Chem. Soc.

1989, 111, 4507.

(60) Bochmann, M.; Lancaster, S. J . Angew. Chem., Int. Ed. Engl.

1994, 33, 1634.

(61) Beck, S.; Prosenc, M. H.; Brintzinger, H. H.; Goretzki, R.;

Herfert, N.; Fink, G. J . Mol. Catal. A 1996, 111, 67.

(62) Koehler, K.; Piers, W. E.; J arvis, A. P.; Xin, S.; Feng, Y.;

Bravakis, A. M.; Collins, S.; Clegg, W.; Yap, G. P. A.; Marder, T. B.

Organometallics 1998, 17, 3557.

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

M. A. Organometallics 1994, 13, 2235.

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

1997, 16, 842.

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

840.

(66) Deck, P. A.; Beswick, C. L.; Marks, T. J . J . Am. Chem. Soc.

1998, 120, 1772.

(67) Vanka, K.; Chan, M. S. W.; Pye, C. C.; Ziegler, T. Organo-

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5338 Organometallics, Vol. 19, No. 25, 2000

Schrock et al.

one type of pseudotetrahedral face of a cation; only one

“free” isotropic [B(C₆F₅)₄]^-ion is likely to be observed.

of a cationic alkyl: i.e., in which the “base” is a main-

group alkyl such as trimethylaluminum. Studies aimed

in these directions are under way.

A plausible scenario is that 6b₁is a tight ion pair in

which the anion is weakly bound on the “apical” CNN

face of the incipient trigonal-bipyramidal species, while

6b₂is a related species in which the anion is associated

more weakly with the cation on another tetrahedral face

and bromobenzene is bound in the apical position

through the lone pairs on the bromide. The process of

converting 6b₁to 6b₂consists essentially of removing

the [B(C₆F₅)₄]^-ion from one pseudo-tetrahedral face of

6b⁺. The observed value of ∆G^qfor that proposed

process in bromobenzene at 298 K is ∼14 kcal mol^-1

(∆H^q) 16.3(5) kcal mol^-1and ∆S^q) 8(2) cal mol^-1K^-1).

This value is essentially the same as the estimated

value for ∆H_ipsin a metallocene cation in chlorobenzene.

We have also considered the possibility that 6b₁is a

dimeric dicationic version of 6b₂(or vice versa) that

contains two bridging methyl groups. In that circum-

stance a labeled methyl group might exchange between

6a and 6b. However, we do not observe any such

exchange. Formation of a dimeric dication also would

seem to be unlikely for steric reasons. Nevertheless, a

dimeric dication is still a possible explanation.

There are some observations that cannot be explained

readily. For example, the observation of more than one

form of 6b₂in dilute bromobenzene/toluene mixtures at

low temperatures might be ascribed to formation of a

toluene solvate as well as a bromobenzene solvate or to

formation of C₁-symmetric “twisted” cations.

Why has a similar process not been observed in

metallocene chemistry? In three-coordinate metallocene

“cations” the process might be observable “indirectly”

by methods employed to study migration of the [MeB-

(C₆F₅)₃]^-ion from one position to another,^66,68but to our

knowledge no [B(C₆F₅)₄]^-salts are stable enough to

study in this manner.

We had hoped to determine whether more than one

form of either an ether adduct or a dimethylaniline

adduct could be observed at low temperatures. Unfor-

tunately, these “strongly solvated”, i.e., five-coordinate,

species crystallize out of bromobenzene/toluene mixtures

at low temperatures. There also is evidence for ad-

ditional complications that revolve around the orienta-

tion of the base in the apical position, “twisting” of the

ligand backbone, etc., as described in Results. In any

case, we suspect that a crowded five-coordinate species

would show little tendency to associate a [B(C₆F₅)₄]^-

anion strongly enough to allow different ion pairs to be

observed at accessible temperatures.

The next step is to explore the behavior of all species

discussed here in terms of olefin polymerization. We

have established already that 2a and 2b, not surpris-

ingly, are inactive for the polymerization of 1-hexene,

while 3, 5, and 6 are all very active for polymerization

of 1-hexene. We will be especially interested in whether

living polymerization characteristics are compromised

to varying degrees (and if so, how) as a consequence of

a mixture of ion pairs being present. As one might

imagine, which ion pairs are formed will be sensitive

to virtually all parameters, including the size of the

alkyl/growing polymer chain. The behavior of 5 as a

catalyst will be especially interesting to explore, since

inter alia it is a model for more complex “base adducts”

Exp er im en ta l Section

Unless otherwise indicated, all manipulations were per-

formed using standard Schlenk techniques or in a N₂-filled

glovebox. Toluene, diethyl ether, and pentane were sparged

with N₂and then passed though columns of activated alumina.

THF was distilled from sodium-benzophenone ketyl. Solvents

were stored in the glovebox over activated 4 Å molecular

sieves. Chlorobenzene (HPLC grade) and deuterated solvents

were sparged with N₂and stored over activated 4 Å molecular

sieves for 2 days prior to use. Chemical shifts are reported in

ppm relative to TMS (¹H, and ¹³C) or external CFCl₃in CDCl₃

(¹⁹F) at room temperature, unless otherwise indicated; J values

are given in Hz. All nonobvious resonances have been assigned

on the basis of ¹H gCOSY, ¹H ROESY (typically with 60 to

300 ms mixing time), ¹³C{¹H} DEPT, and ¹H-¹³C HMQC.

Some resonances in ¹³C spectra are not listed. The temperature

of the NMR probe was obtained by standardization with

methanol or ethylene glycol. Quantitative line-shape analysis

(LSA) was carried out using gNMR V3.6.5 software (Peter H.

M. Budzelaar, IvorySoft 1992: Palo Alto, CA). High-resolution

MS was recorded on a Finnigan MAT 8200 Sector mass

spectrometer. Elemental analyses were performed by H. Kolbe,

Mikroanalytisches Laboratorium (Mu¨hlheim an der Ruhr,

Germany). X-ray data were collected on

a Bruker CCD

diffractometer with λ(Mo KR) ) 0.710 73 Å and solved using

a full-matrix least-squares refinement on F². Grignard re-

agents and organolithium reagents were prepared in the

normal fashion and titrated with 2-butanol in the presence of

1,10-phenanthroline prior to use.

(MesNHCH₂CH₂)₂NH (H₂[N₂NH]). A 2 L Schlenk flask

was charged with diethylenetriamine (23.450 g, 0.227 mol),

mesityl bromide (90.51 g, 0.455 mol), tris(dibenzylidene-

acetone)dipalladium(0) (1.041 g, 1.14 mmol), rac-2,2′-bis-

(diphenylphosphino)-1,1′-binaphthyl (2.123 g, 3.41 mmol),

sodium tert-butoxide (65.535 g, 0.682 mol), and toluene (800

mL). The reaction mixture was heated to 95 °C in an oil bath

and stirred for 4 days. All solvent was removed in vacuo at

∼50 °C to leave a dark brown solid residue. The residue was

dissolved in diethyl ether (1 L), and the solution was washed

three times with water (1 L) and saturated aqueous NaCl (0.5

L) and dried over magnesium sulfate. Removal of the ether in

vacuo left a red oil, which was further heated at 70 °C

overnight (∼12 h) at 40 mTorr. The red oil crystallized upon

cooling to room temperature to give red needlelike crystals;

yield 71.10 g, 92%. The red crystals were pure, as judged by

¹H NMR, and were used in subsequent reactions. The product

was recrystallized from pentane to afford yellow crystals; yield

65.45 g (85%): ¹H NMR (C₆D₆) δ 6.83 (s, 4, Ar), 3.39 (br s, 2,

ArNH), 2.86 (t, 4, CH₂), 2.49 (t, 4, CH₂), 2.27 (s, 12, Me_o), 2.21

(s, 6, Me_p), 0.68 (br s, 1, CH₂NHCH₂); ¹³C NMR (C₆D₆) δ 143.74

(C, Ar), 131.35 (C, Ar), 129.83 (C, Ar), 129.55 (CH, Ar), 50.17

(CH₂), 48.56 (CH₂), 20.70 (Me_p), 18.51 (Me_o); IR (CHCl₃) cm^-1

3357 (NH stretch, medium); high-resolution MS (EI, 70 eV)

339.267 32 (calcd 339.267 448). Anal. Calcd for C₂₂H₃₃N₃: C,

77.83; H, 9.80; N; 12.38. Found: C, 77.85; H, 9.72; N, 12.31.

(MesNHCH₂CH₂)₂NMe (H₂[N₂NMe]). A 250 mL Schlenk

flask was charged with H₂[N₂NH] (10.0 g, 29.45 mmol), K₂CO₃

(15 g), and acetonitrile (100 g). This solution was cooled to 0

°C, and MeI (1.9 mL, 30.52 mmol) was added. The solution

was warmed to room temperature and was stirred for 20 h.

The reaction mixture was extracted with pentane/water (100

mL/100 mL) in air. The pentane layer was separated, and the

water was washed with pentane (2 × 50 mL). The organic

phases were combined, and the solvent was removed in vacuo;

yield 8.43 g (81%): ¹H NMR (300 MHz, CDCl₃) δ 7.04 (s, 4,

CH), 3.29 (t, 4, J _HH) 6.6, CH₂), 2.84 (t, 4, J _HH) 6.6, CH₂),

Activation of [(MesNCH₂CH₂)₂NR]ZrMe₂Species

Organometallics, Vol. 19, No. 25, 2000 5339

2.50 (s, 12, CH₃), 2.48 (s, 3, NCH₃), 2.45 (s, 6, CH₃); ¹³C NMR

(121 MHz, CDCl₃) δ 143.91 (Ar), 130.79 (Ar), 129.47 (Ar),

129.24 (Ar), 58.41 (CH₂), 46.09 (CH₂), 41.42 (NCH₃), 20.57

(CH₃), 18.49 (CH₃).

30 min. The mixture was stirred for 60 min, and MgClBr was

filtered off. The toluene and ether were removed under

vacuum, and the solids were extracted with toluene (200 mL).

The mixture was filtered and the volume of toluene was

reduced to 10 mL. Pentane (250 mL) was added, which induced

precipitation of a pale brown solid. The solid product was

isolated by filtration, washed with 50 mL of cold pentane, and

dried under vacuum; yield 15.20 g (86%): ¹H NMR (C₆D₆) δ

6.99 (s, 2, Ar), 6.97 (s, 2, Ar), 3.31 (m, 2, CH₂), 3.13 (m, 2, CH₂),

2.53 (s, 6, Me_o), 2.43 (s, 6, Me_o), 2.36 (m, 4, CH₂), 2.21 (s, 6,

Me_p), 1.16 (br s, 1, NH), 0.24 (s, 3, ZrMe_eq), 0.07 (s, 3, ZrMe_ax);

¹³C NMR (C₆D₆) δ 146.56 (C, Ar), 136.07 (C, Ar), 135.55 (C,

Ar), 134.23 (C, Ar), 130.29 (CH, Ar), 129.98 (CH, Ar), 57.46

(CH₂), 51.27 (CH₂), 42.45 (ZrMe_eq), 39.63 (ZrMe_ax), 21.44 (Me_p),

19.39 (Me_o), 19.28 (Me_o). Anal. Calcd for C₂₄H₃₇N₃Zr: C, 62.83;

H, 8.13; N; 9.16. Found: C, 62.91; H, 8.02; N, 9.04. Single

crystals of [N₂NH]ZrMe₂were grown from a mixture of diethyl

ether, toluene, and hexamethyldisiloxane at -30 °C.

[N₂NH]Zr (NMe₂)₂. Solid Zr(NMe₂)₄(3.12 g, 11.7 mmol) was

added to a slurry of H₂[N₂NH] (4.1 g, 12.1 mmol) in 20 mL of

pentane. The solution was stirred for 24 h. The precipitated

product was filtered off, washed with cold pentane (2 × 10

mL), and dried in vacuo; yield 3.56 g, 59%: ¹H NMR (C₆D₆) δ

6.96 (s, 2, Ar), 6.95 (s, 2, Ar), 3.36 (m, 2, CH₂), 3.05 (s, 6, NMe),

3.01 (m, 2, CH₂), 2.61 (m, 4, CH₂), 2.47 (s, 6, Me_o), 2.45 (s, 6,

Me_p), 2.28 (s, 6, NMe), 2.21 (s, 6, Me_o), 1.80 (br s, 1, NH); ¹³C

NMR (C₆D₆) δ 150.48 (C, Ar), 134.49 (C, Ar), 132.06 (C, Ar),

129.61 (CH, Ar), 55.59 (CH₂), 49.26 (CH₂), 44.62 (NMe), 41.27

(NMe), 21.31 (Me_p), 19.52 (Me_o). Anal. Calcd for C₂₆H₄₃N₅Zr:

C, 60.42; H, 8.39; N; 13.55. Found: C, 60.31; H, 8.29; N, 13.39.

[N₂NMe]Zr (NMe₂)₂. Solid Zr(NMe₂)₄(3.10 g, 11.59 mmol)

was added to a solution of H₂[N₂NMe] (4.10 g, 11.59 mmol) in

20 mL of pentane. The solution was stirred for 24 h and

filtered. The solid product was washed with pentane and dried;

yield 4.24 g (69%): ¹H NMR (300 MHz, C₆D₆) δ 6.95 (s, 4, CH),

3.41 (m, 2, CH₂), 3.10 (2, 6, N(CH₃)₂), 3.20 (m, 2, CH₂), 2.78

(m, 2, CH₂), 2.49 (s, 6, CH₃), 2.51 (s, 6, N(CH₃)₂), 2.37 (s, 6,

CH₃), 2.33 (m, 2, CH₂), 2.22 (s, 3, NCH₃), 2.21 (s, 6, CH₃).

[N₂NH]Zr Cl₂. (CH₃)₃SiCl (0.66 mL, 5.16 mmol) was added

to a solution of [N₂NH]Zr(NMe₂)₂(1.21 g, 2.33 mmol) in 20

mL of diethyl ether. The reaction mixture was stirred for ∼16

h. The precipitated product was filtered off and washed with

pentane; yield 1.07 g (92%): ¹H NMR δ 6.88 (s, 2, Ar), 6.83 (s,

2, Ar), 3.32 (m, 2, CH₂), 2.86 (m, 2, CH₂), 2.50 (s, 6, Me_o), 2.45

(m, 4, CH₂), 2.40 (s, 6, Me_o), 2.20 (br s, 1, NH), 2.13 (s, 6, Me_p);

¹³C NMR δ 146.28 (C, Ar), 135.52 (C, Ar), 134.48 (C, Ar), 134.14

(C, Ar), 130.48 (CH, Ar), 130.28 (CH, Ar), 57.13 (CH₂), 49.43

(CH₂), 21.33 (Me_p), 19.49 (Me_o), 19.41 (Me_o). Anal. Calcd for

[N₂NH]Zr (¹³CH₃)₂. To a stirred suspension of [N₂NH]ZrCl₂

(1.00 g, 2.00 mmol) in diethyl ether (30 mL) at -30 °C was

added ¹³CH₃MgI (2.3 M in Et₂O, 1.84 mL, 4.2 mmol). The

mixture was stirred for 20 min without further cooling. The

solvent was then removed in vacuo and the residue dissolved

in toluene (30 mL). This solution was then treated with 1,4-

dioxane (680 mg, 7.71 mmol), which led to formation of a white

precipitate. The slurry was filtered through Celite, and the

solvent was removed from the filtrate in vacuo, yielding ¹³C-

labeled 1a ; yield 0.54 g (58%). The product can be recrystal-

lized from a mixture of ether and pentane at -30 °C: ¹H NMR

(C₆D₆) δ 6.99 (s, 2, CH), 6.97 (s, 2, CH), 3.33 (m, 2, CHH), 3.12

(m, 2, CHH), 2.53 (s, 6, p-CH₃), 2.43 (s, 6, o-CH₃), 2.36 (m, 4,

CHH), 2.21 (s, 6, o-CH₃), 1.2 (m, NH), 0.23 (d, J _CH) 136,

Zr¹³CH₃), 0.07 (d, J _CH) 135, Zr¹³CH₃); ¹³C NMR (C₆D₆) δ 42.49

(ZrCH₃), 39.43 (ZrCH₃).

C

₂₂H₃₁Cl₂N₃Zr: C, 52.89; H, 6.25; N; 8.41. Found: C, 52.76;

[N₂NMe]Zr Me₂(1b). Meth od A. Methyllithium (0.15 mL,

1.4 M in Et₂O, 0.21 mmol) was added to a slurry of [N₂NH]-

ZrMe₂(0.098 g, 0.21 mmol) in Et₂O (3 mL) at -30 °C. The

white slurry immediately turned pale yellow, and the mixture

became homogeneous. The solution was warmed and stirred

at room temperature for 1 h and then chilled to -30 °C. Methyl

iodide (0.045 g, 0.32 mmol, 1.5 equiv) was added to the cold

solution, and the reaction mixture was stirred at room tem-

perature for 1 h. All volatile components were removed in

vacuo, and the solid residue was extracted with toluene (5 mL).

Toluene was removed from the extract in vacuo, and the

residue was redissolved in pentane (10 mL). The volume of

the solution was reduced in vacuo to ∼2 mL to afford a

colorless crystalline solid. The concentrated solution was kept

at -30 °C for 2 h, and the crystalline product was collected;

yield 64 mg (63%).

Meth od B. To 10.00 g of {H₂[N₂NH]}ZrCl₄(17.4 mmol)

(prepared from H₂[N₂NH] and ZrCl₄in toluene) suspended in

250 mL of Et₂O in a 500 mL round-bottom flask at -40 °C

was added dropwise 65.5 mL of MeLi (1.4 M, 91.7 mmol) over

30 min with stirring. The mixture was warmed to room

temperature and stirred for 30 min. The mixture was cooled

to -40 °C, and 3.14 g of MeI (22.1 mmol) in 5 mL ether was

added dropwise with stirring over 5 min. The mixture was

warmed to room temperature, and the ether was removed in

vacuo. The product was extracted with toluene (250 mL), and

the extract was filtered to remove LiCl and LiI. The filtrate

volume was reduced to 30 mL in vacuo, and 250 mL of pentane

was added, causing precipitation of a pale brown solid. The

solid product was isolated by filtration, washed with 50 mL of

cold pentane, and dried under vacuum; yield 7.82 g (95%).

Meth od C. A slurry of [N₂NMe]ZrCl₂(1.02 g, 1.99 mmol)

in 20 mL of Et₂O was cooled to -20 °C. This mixture was then

treated with MeMgBr (1.5 mL, 3 M in Et₂O, 4.5 mmol). The

slurry became homogeneous, and a solid precipitated. The

mixture was stirred for 10 min, and then all solvents were

removed in vacuo. The residue was dissolved in 20 mL of

H, 6.35; N, 8.48.

[N₂NMe]Zr Cl₂. (CH₃)₃SiCl (4.0 mL, 31.3 mmol) was added

to a solution of [N₂NMe]Zr(NMe₂)₂(4.12 g, 7.76 mmol) in 50

mL of diethyl ether. The reaction mixture was stirred for 24

h. The precipitated product was filtered off and washed with

pentane (40 mL); yield 3.52 g (88%).

[N₂NH]Zr Me₂(1a ). Meth od A. Methylmagnesium iodide

(0.1 mL, 3 M in diethyl ether, 2 equiv) was added to a cold

solution (-30 °C) of [N₂NH]ZrCl₂(75 mg, 0.150 mmol) in

diethyl ether (5 mL). The reaction mixture was slowly warmed

to room temperature and stirred for 10 min. Proton NMR

revealed that the product had formed cleanly. Dioxane (5

drops) was added, and the precipitate was removed via

filtration. The filtrate was concentrated in vacuo to ∼1 mL.

Pentane (2 mL) was added to the concentrated filtrate in order

to precipitate white solid product; yield 69 mg (76%).

Meth od B. Solid ZrCl₄(0.709 g, 0.304 mmol) was added in

portions to a diethyl ether solution (20 mL) of H₂[N₂NH] (1.033

g, 0.304 mmol) at -30 °C with vigorous stirring. The solution

was warmed and stirred at room temperature. Pale yellow

solid precipitated gradually over a period of 1 h. The yellow

suspension was cooled to -30 °C, and methylmagnesium iodide

(4.1 mL, 3 M in diethyl ether, 4.1 equiv) was added. Gas

evolved and the solution immediately turned white and cloudy.

The solution was stirred at room temperature for 10 min, and

then 1,4-dioxane (1.2 g, 4.5 equiv) was added. The reaction

mixture was filtered through Celite, which was washed with

diethyl ether (2 × 10 mL). The pale yellow solution was

concentrated in vacuo to ∼20 mL and chilled to -30 °C for 1

h to give colorless crystals; yield (3 crops) 0.571 g (41%).

Meth od C. H₂[N₂NH] (10.798 g, 31.8 mmol) was dissolved

in 250 mL of toluene in a 500 mL round-bottom flask. ZrCl₄

(7.411 g, 31.8 mmol) was added as a solid, and the mixture

was heated to 80 °C and stirred for 24 h. The mixture was

cooled to room temperature, and 43.5 mL of MeMgBr (3.0 M

in ether, 130.3 mmol) was added dropwise with stirring over

5340 Organometallics, Vol. 19, No. 25, 2000

Schrock et al.

toluene, and 0.5 mL of 1,4-dioxane was added. The solution

was stirred for 10 min and then filtered through Celite. The

solvent was removed from the filtrate in vacuo; yield 0.89 g

(95%): ¹H NMR δ 6.99 (s, 2, Ar), 6.95 (s, 2, Ar), 3.62 (m, 2,

CH₂), 2.98 (m, 2, CH₂), 2.66 (m, 2, CH₂), 2.47 (s, 6, Me_p), 2.44

(s, 6, Me_o), 2.20 (s, 6, Me_o), 2.12 (m, 2, CH₂), 2.01 (s, 3, NMe),

0.26 (s, 3, ZrMe_eq), 0.23 (s, 3, ZrMe_ax); ¹³C NMR δ 146.13 (C,

Ar), 136.63 (C, Ar), 136.08 (C, Ar), 134.32 (C, Ar), 130.36 (CH,

Ar), 130.05 (CH, Ar), 61.14 (CH₂), 55.89 (CH₂), 43.31 (ZrMe),

40.62 (ZrMe), 37.10 (NMe), 21.42 (Me_p), 19.20 (Me_o), 19.09

(Me_o). Anal. Calcd for C₂₅H₃₉N₃Zr: C, 63.51; H, 8.31; N; 8.89.

Found: C, 63.26; H, 8.14; N, 8.85. X-ray-quality crystals were

grown from a mixture of ether and pentane at -30 °C.

[N₂N(*CH₃)]Zr (^#CH₃)₂. To a stirred suspension of [N₂NH]-

Zr(¹³CH₃)₂(0.43 g, 0.933 mmol) in Et₂O (15 mL) at -30 °C

was added a 1.6 M solution of LiMe in Et₂O (0.60 mL, 0.96

mmol). The resulting pale yellow cloudy solution that formed

was stirred for 20 min while the temperature was allowed to

increase to room temperature. The solution was then cooled

to -30 °C, and ¹³CH₃I (85 µL, 1.4 mmol) was added dropwise.

The mixture was stirred for 30 min. The solvent was removed

in vacuo, and the residue was extracted with toluene. The

toluene was removed in vacuo, leaving a crystalline tan solid,

which was washed with cold pentane (4 mL) and dried in

vacuo; yield 0.38 g (81%): ¹H NMR (300 MHz, C₆D₆/C₆D₅Br)

δ 6.92/6.87 (s, 2, CH), 6.45/6.85 (s, 2, CH), 3.62/3.71 (m, 2,

CHH), 2.90/3.05 (m, 2, CHH), 2.65/2.93 (m, 2, CHH), 2.47/2.39

(s, 6, p-CH₃), 2.44/2.34 (s, 6, o-CH₃), 2.20/2.14 (s, 6, o-CH₃),

2.15/2.14 (m, 2, CHH), 2.01/2.29 (d, J _CH) 136.3, N¹³CH₃), 0.26/

{[N₂NMe]Zr (CH₃)(NMe₂P h )}[B(C₆F ₅)₄] (3b). To a solu-

tion of [N₂NMe]Zr(CH₃)₂(0.20 g, 0.42 mmol) in chlorobenzene

(8 mL) at -30 °C was added [NMe₂Ph][B(C₆F₅)₄] (0.34 g, 0.42

mmol). The resulting orange solution was stirred for 90 min,

filtered, and evaporated to dryness. The resulting orange oil

was vigorously stirred with pentane (5 mL), yielding {[N₂NMe]-

Zr(CH₃)(NMe₂Ph)}[B(C₆F₅)₄] as an orange powder which was

washed with pentane (3 × 15 mL) and vacuum-dried; yield

0.53 g (98%): ¹H NMR (300 MHz, C₆D₅Br) δ 6.81 (s, 2, CH

syn with respect to NCH₃), 6.78 (s, 2, CH), 6.42 (broad, H, anil-

p-CH), 6.29 (broad, 2, anil-m-CH), 5.66 (d, 2, J _HH) 8.5, anil-

o-CH), 3.29 (m, 2, CHH), 2.97 (m, 2, CHH), 2.92 (m, 2, CHH),

2.58 (m, 2, CHH), 2.40 (s, 3, J _HC) 138, NCH₃), 2.32 (broad, 6,

PhNCH₃), 2.20 (s, 6, p-CH₃), 2.13 (s, 6, o-CH₃syn with respect

to NCH₃), 1.89 (s, 6, o-CH₃), 0.07 (broad, 3, J _CH) 119, ZrCH₃);

¹³C NMR (126 MHz, C₆D₅Br) δ 130.3 (CH syn with respect to

NCH₃), 130.2 (CH), 56.7 (CH₂), 55.3 (CH₂), 46.47 (NCH₃), 37.0

(broad, ZrCH₃), 20.72 (p-CH₃), 18.49 (o-CH₃syn with respect

to NCH₃), 17.73 (o-CH₃); ¹⁹F (471 MHz, C₆D₅Br) δ -131.71

(broad, 2, 2-CF), -162.03 (t, 1, J _FF) 2124, 4-CF), -165.88

(broad, 2, 3-CF). Anal. Calcd for C₅₆H₄₇N₄BF₂₀Zr: C, 53.47;

H, 3.77; N, 4.45. Found: C, 53.56; H, 3.69; N, 4.41. The ¹³C-

labeled complexes were prepared by identical procedures.

P r ep a r a tion of Im p u r e {[{[2-(CH₂)-4,6-(CH₃)₂C₆H₂]N-

CH ₂CH ₂}N(CH ₂CH ₂NMes)(CH ₃)]Zr (NMe₃P h )}[B(C₆F ₅)₄]

(4b). To a solution of [N₂NMe]Zr(CH₃)₂(0.10 g, 0.21 mmol) in

chlorobenzene (2 mL) at -30 °C was added a suspension of

[NMe₂Ph][B(C₆F₅)₄] (0.17 g, 0.21 mmol) in chlorobenzene (2

mL), also at -30 °C. The resulting orange solution was stirred

for 1 h, filtered, and evaporated to dryness. The resulting

foamy residue was treated with pentane (5 mL) to afford the

product as an off-yellow powder, which was washed with

pentane (3 × 10 mL) and vacuum-dried; yield 0.25 g (95%):

¹H NMR (500 MHz, C₆D₅Br) δ 6.92 (s, 1, CH), 6.77 (m, 1, anil-

p-CH), 6.76 (m, 2, anil-m-CH), 6.72 (s, 1, CH), 6.71 (s, 1, 5-CH),

6.08 (s, 1, 3-CH), 5.75 (d, 2, J _HH) 7.5, anil-o-CH), 4.34 (m, 1,

CHH), 3.81 (m, 1, CHH), 3.23 (m, 1, CHH), 3.02 (m, 1, CHH),

2.78 (m, 1, CHH), 2.70 (m, 1, CHH), 2.60 (m, 1, CHH), 2.55

(m, 1, CHH), 2.53 (s, 3, NCH₃), 2.39 (d, 1, J _HH) 12.5, ZrCHH),

2.24 (s, 3, o-CH₃), 2.21 (s, 3, p-CH₃), 2.18 (s, 3, 9-CH₃), 2.09 (s,

3, anil-NCH₃), 2.06 (s, 3, 8-CH₃), 1.92 (s, 3, o-CH₃), 1.91 (s, 3,

anil-NCH₃), 0.79 (d, 1, J _HH) 12.5, ZrCHH); ¹³C NMR (121

MHz, C₆D₅Br) δ 132 (s, CH anil), 130.55 (CH), 130.02 (CH),

129.95 (5-CH), 126.78 (3-CH), 114.18 (anil-o-CH), 68.90 (ZrCH₂),

65.32 (NCH₂), 60.29 (NCH₂), 55.76 (NCH₂), 54.70 (NCH₂),

46.53 (anil-NCH₃), 42.23 (anil-NCH₃), 40.43 (NCH₃), 20.79 (9-

CH₃), 20.65 (p-CH₃), 19.29 (8-CH3), 18.94 (o-CH₃), 18.64 (o-

CH₃).

0.03 (s, d, 3, J _CH) 114, Zr^2/3×13CH₃), 0.24/-0.05 (s, d, 3, J _CH

)

114, Zr^2/3×13CH₃); ¹³C NMR (121 MHz, C₆D₆/C₆D₅Br) δ 43.31/

42.52 (s, ZrCH₃), 40.63/39.89 (s, ZrCH₃), 37.09/36.78 (s, NCH₃).

{[N₂NH]Zr Me(Et₂O)}[B(C₆F ₅)₄] (2a ). A solution of [Ph₃C]-

[B(C₆F₅)₄] (0.25 g, 0.27 mmol) in PhCl (3 mL) at -30 °C was

added to a solution of 1a (0.13 g, 0.75 mmol) in PhCl (3 mL)

at -30 °C. The resulting orange solution was stirred for 5 min,

and then Et₂O (1 mL) was added. The solution was filtered,

and the filtrate was evaporated to dryness in vacuo. The waxy

red residue was triturated with pentane (5 mL), leaving a

yellow powder which was washed with pentane (3 × 10 mL)

and then vacuum-dried; yield 0.28 g (86%): ¹H NMR (500

MHz, C₆D₅Br) δ 6.79 (s, 2, CH), 6.72 (s, 2, CH), 3.41 (m, 2,

CHH), 3.15 (m, 2, CHH), 2.97 (m, 2, CHH), 2.82 (m, 2, CHH),

2.77 (q, 4, J _HH) 6.9, °CH₂), 2.19 (s, 6, p-CH₃), 2.13 (s, 6, o-CH₃),

1.91 (s, 6, o-CH₃), 1.03 (m, NH), 0.25 (t, 6, J _HH) 6.9, CH₂CH₃),

0.13 (s, 3, ZrCH₃); ¹⁹F (471 MHz, C₆D₅Br) δ -132.16 (br, 2,

o-CF), -162.20 (t, 1, J ) 21.4, p-CF), -166.20 (broad, 2, m-CF).

Anal. Calcd for C₅₁H₄₄BF₂₀N₃OZr: C, 51.80; H, 3.71; N, 4.51.

Found: C, 51.64; H, 3.82; N, 4.37.

[{[N₂NMe]Zr (CH₃)}₂(µ-CH₃)][B(C₆F ₅)₄] (5b). To a solution

of [Ph₃C][B(C₆F₅)₄] (0.15 g, 0.16 mmol) in chlorobenzene (3 mL)

at -30 °C was added a solution of [N₂NMe]Zr(CH₃)₂(0.15 g,

0.32 mmol) in chlorobenzene (3 mL) at -30 °C. The resulting

pale yellow solution was stirred for 15 min at ∼20 °C. The

solution was then added dropwise to pentane (60 mL), yielding

5b as an off-white precipitate. The product was separated by

filtration, washed with pentane (2 × 3 mL), and vacuum-dried;

yield 0.23 g (87%): ¹H NMR (500 MHz, -25 °C, C₆D₅Br) δ

6.95 (s, 2, CH syn with respect to NCH₃), 6.88 (s, 2, CH), 6.80

(s, 2, CH syn with respect to NCH₃), 6.75 (s, 2, CH), 3.26 (m,

2, CHH), 3.19 (m, 2, CHH), 2.99 (m, 2, CHH), 2.94 (m, 2, CHH),

2.64 (m, 4, CHH), 2.34 (m, 4, CHH), 2.32 (s, 6, p-CH₃), 2.28 (s,

6, p-CH₃), 2.23 (s, 6, o-CH₃syn with respect to NCH₃), 2.19 (s,

6, o-CH₃syn with respect to NCH₃), 2.11 (s, 6, NCH₃), 1.65 (s,

6, o-CH₃), 1.42 (s, 6, o-CH₃), -0.38 (s, 6, J _CH) 115, ZrCH₃),

-0.89 (s, 3, J _CH) 133, ZrCH₃Zr); ¹³C NMR (126 MHz, -25

°C, C₆D₅Br) δ 45.02 (s, NCH₃), 41.23 (s, ZrCH₃), 40.11 (s,

{[N₂NMe]Zr Me(Et₂O)}[B(C₆F ₅)₄] (2b). Complex 2b was

prepared from 1b (0.24 g, 0.508 mmol) and [Ph₃C][B(C₆F₅)₄]

(0.47 g, 0.508 mmol) in PhCl (5 mL) by following the procedure

described for 2a ; yield 0.56 g (92%): ¹H NMR (500 MHz, C₆D₅-

Br) δ 6.79 (s, 2, CH syn with respect to NCH₃), 6.72 (s, 2, CH),

3.42 (m, 2, CHH), 3.18 (m, 2, CHHNCH₃), 2.98 (m, 2, CHH),

2.79 (q, 4, J _HH) 6.9, OCH₂), 2.65 (m, 2, CHHNCH₃), 2.38 (s,

3, J _CH) 138, NCH₃), 2.39 (s, 6, o-CH₃syn with respect to

NCH₃), 2.13 (s, 6, o-CH₃), 1.93 (s, 6, o-CH₃), 0.22 (t, 6, J _HH

)

138, 6.9, CH₂CH₃), 0.19 (s, 3, J _CH) 115.3, ZrCH₃); ¹³C NMR

(126 MHz, C₆D₅Br) δ 149.0 (C), 137.7 (C), 135.8 (C), 134.5 (C),

130.6 (CH syn with respect to NCH₃), 130.2 (CH), 67.79

(OCH₂), 57.54 (CH₂), 53.83 (CH₂NCH₃), 45.69 (NCH₃), 39.81

(ZrCH₃), 20.58 (o-CH₃syn with respect to NCH₃), 18.28 (p-

CH₃), 17.99 (o-CH₃), 11.78 (CH₂CH₃); ¹⁹F (471 MHz, C₆D₅Br):

δ -132.08 (broad, 2, o-CF), -162.41 (t, 1, J ) 21.4, p-CF),

-166.28 (broad, 2, m-CF). Anal. Calcd for C₅₂H₄₆BF₂₀N₃OZr:

C, 51.58; H, 3.83; N, 3.47. Found: C, 51.68; H, 3.92; N, 3.41.

Crystals of 2b suitable for X-ray diffraction were grown from

pentane/chlorobenzene at -25 °C. The ¹³C-labeled complex was

prepared from ¹³C-labeled 1b by following an identical proce-

dure.

1

ZrCH₃Zr); H NMR (500 MHz, 20 °C, C₆D₅Br) δ 6.89 (broad,

4, CH), 6.82 (broad, 4, CH syn with respect to NCH₃), 3.27 (m,

4, CHH), 3.01 (m, 4, CHH), 2.72 (m, 4, CHH), 2.40 (m, 4, CHH),

2.28 (s, 12, p-CH₃), 2.21 (s, 12, o-CH₃syn with respect to

NCH₃), 2.18 (s, 6, NCH₃), 1.58 (broad, 12, o-CH₃), -0.36 (s, 6,

Activation of [(MesNCH₂CH₂)₂NR]ZrMe₂Species

Organometallics, Vol. 19, No. 25, 2000 5341

J _CH) 115, ZrCH₃), -0.85 (s, 3, J _CH) 133, ZrCH₃Zr); ¹³C NMR

(126 MHz, 20 °C, C₆D₅Br) δ 45.12 (s, NCH₃), 41.62 (s, ZrCH₃),

40.15 (s, ZrCH₃Zr); ¹⁹F (471 MHz, 20 °C, C₆D₅Br) δ -131.65

(broad, 2, o-CF), -162.10 (t, 1, J ) 21.2, p-CF), -165.92 (broad,

2, m-CF). Anal. Calcd for C₇₃H₇₅BF₂₀N₆Zr₂: C, 54.47; H, 4.70;

N, 5.22. Found: C, 54.55; H, 4.76; N, 5.09. Single crystals

of [{[N₂NMe]Zr(CH₃)}₂(µ-CH₃)][B(C₆F₅)₄] suitable for X-ray

diffraction were grown from a mixture of toluene and chloro-

benzene at -25 °C.

(500 MHz, 20 °C, C₆D₅Br): δ 6.70 (s, 4, CH), 3.53 (m, 2, CHH),

3.34 (m, 2, CHH), 3.05 (m, 2, CHH), 2.73 (m, 2, CHH), 2.38 (s,

3, J _CH) 138, NCH₃), 2.18 (br s, 6, o-CH₃), 2.01 (br, 6, p-CH₃),

1.90 (br, 6, o-CH₃), 0.16 (d, 3, J _CH) 115, ZrCH₃). ¹³C NMR of

6b₁(126 MHz, 20 °C, C₆D₅Br): δ 47.83 (br, ZrCH₃), 45.74 (s,

NCH₃). The ¹³C-labeled complex {[N₂N(*CH₃)]Zr(^#CH₃)}⁺was

prepared from ¹³C-labeled 1b by the same procedure.

Lin e Sh a p e An a lyses. The line shape analysis in Figure

8a was carried out by considering an exchange between two

sites with a population difference calculated according to the

observed or extrapolated equilibrium constant and a band-

width of 4 Hz.

Obser va tion of {[N₂NH]Zr (CH₃)}[B(C₆F ₅)₄] (6a ₂). To a

solution of 1a (0.02 g, 46 µmol) in C₆D₅Br (0.4 mL) at -30 °C

was added a solution of [Ph₃C][B(C₆F₅)₄] (0.04 g, 46 µmol) in

C₆D₅Br (0.4 mL), also at -30 °C. The resulting orange solution

was transferred to an NMR tube: ¹H NMR (500 MHz, -25

°C, C₆D₅Br) δ 6.82 (s, 4, CH), 3.07 (m, 2, CHH), 2.90 (m, 2,

CHH), 2.81 (s, NH), 2.70 (m, 2, CHH), 2.66 (m, 2, CHH), 2.23

(s, 6, p-CH₃syn to NH), 2.04 (s, 6, o-CH₃), 1.97 (s, 6, o-CH₃

The line shape analysis for [{[N₂NMe]Zr(CH₃)}₂(µ-CH₃)]-

[B(C₆F₅)₄] was carried out (gNMR software) by modeling the

two coalescing o-CH₃resonances near 1.50 ppm in a spectrum

in C₆D₅Br at 500 MHz. A bandwidth of 3 Hz was employed.

The calculated values for k in s^-1(temperature T in K) are

12 (248.3), 25 (258.6), 70 (268.8), 180 (279.4), 400 (289.7),

810 (299.7), 1900 (309.3), 4100 (318.8), and 7000 (329.6). An

1

syn to NCH₃), -0.13 (s, 3, J _CH) 117, ZrCH₃); H NMR (500

MHz, 20 °C, C₆D₅Br) δ 6.82 (br, 4, CH), 3.13 (br, 4, CHH),

2.78 (m, 4, CHH), 2.7 (br, NH), 2.21 (br, 6, p-CH₃), 2.03 (br, 6,

Eyring plot yielded ∆H^q) 52.3 ( 1.3 kJ mol^-1and ∆S^q

-14 ( 5 J K^-1mol^-1

)

o-CH₃), 1.98 (br, 6, o-CH₃), -0.08 (s, 3, J _CH) 117, ZrCH₃); ¹³

C

.

NMR (126 MHz, -25 °C, C₆D₅Br) δ 31.29 (br, ZrCH₃); ¹³C NMR

(126 MHz, 20 °C, C₆D₅Br) δ 31.7 (br, ZrCH₃). The ¹³C-labeled

complex {[N₂NH]Zr(¹³CH₃)}⁺was prepared from ¹³C-labeled

1a by the same procedure.

Ack n ow led gm en t. We thank the Department of

Energy (Contract No. DE-FG02-86ER13564) and

Exxon Corp. for supporting this research. A.L.C. thanks

The Ministerio de Educacio´n y Cultura (Spain) for a

postdoctoral fellowship and Dr. J eff Simpson of the

MIT Spectroscopy Laboratory for assistance with NMR

techniques.

Obser va tion of {[N₂NMe]Zr (CH₃)}[B(C₆F ₅)₄] (6b₁/6b₂).

To a solution of 1b (20 mg, 42 µmol) in C₆D₅Br (0.4 mL) at

-30 °C was added a solution of [Ph₃C][B(C₆F₅)₄] (39 mg, 42

µmol) in C₆D₅Br (0.4 mL), also at -30 °C. The resulting orange

solution was transferred to an NMR tube. ¹H NMR of 6b₂(500

MHz, -25 °C, C₆D₅Br): δ 6.66 (s, 2, CH), 6.65 (m, 2, CH), 3.45

(m, 2, CHH), 3.29 (m, 2, CHH), 2.98 (m, 2, CHH), 2.67 (m, 2,

CHH), 2.32 (s, J _CH) 139, NCH₃), 2.16 (s, 6, o-CH₃syn to

Su p p or tin g In for m a tion Ava ila ble: Text giving experi-

mental procedures, fully labeled ORTEP drawings, and tables

giving crystal data and structure refinement details, atomic

coordinates, bond lengths and angles, and anisotropic dis-

placement parameters for [N₂NH]ZrMe₂, {[N₂NMe]ZrMe-

(ether)}[B(C₆F₅)₄], and [[N₂NMe]ZrMe}₂(µ-CH₃)][B(C₆F₅)₄]. This

material is available free of charge via the Internet at http://

pubs.acs.org. Supporting X-ray information for [N₂NMe]ZrMe₂

can be found in the preliminary communication.⁴

NCH₃), 2.10 (s, 6, p-CH₃), 1.88 (s, 6, o-CH₃), 0.15 (s, J _CH

)

115, ZrCH₃). ¹³C NMR of 6b₂(126 MHz, -25 °C, C₆D₅Br): δ

1

47.24 (s, ZrCH₃), 45.57 (s, NCH₃). H NMR of 6b₁(500 MHz,

-25 °C, C₆D₅Br): δ 6.82 (s, 4, CH), 3.13 (m, 2, CHH), 2.78 (br,

4, CHH), 2.41 (br, 2, CHH), 2.29 (s, J _CH) 139, NCH₃), 2.23 (s,

6, p-CH₃), 2.08 (s, 6, o-CH₃), 2.02 (s, 6, o-CH₃syn to NCH₃),

-0.01 (s, 3, J _CH) 117, ZrCH₃). ¹³C NMR of 6b₁(126 MHz,

-25 °C, C₆D₅Br): δ 46.51 (s, NCH₃), 33.52 (s, ZrCH₃). ¹⁹F

of 6b₁(471 MHz, -25 °C, C₆D₅Br): δ -132.04 (br, 2, o-CF),

1

-161.38 (br, 1, p-CF), -165.37 (br, 2, m-CF). H NMR of 6b₁

OM0004996

Article Doi

Preparation and activation of complexes of the type [((mesityl)NCH2CH2)2NX]ZrMe2 (X = H, Me) with [Ph3C][B(C6F5)4] or [PhNMe2H][B(C6F5

DOI: 10.1021/om0004996

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