Neutral and cationic group 4 metal compounds containing octamethyldibenzotetraazaannulene (Me8taa2-) ligands. Synthesis and reactivity of (Me8taa)MX2 and (Me8taa)MX+ complexes (M = Zr, Hf;

382

Organometallics 1998, 17, 382-397

Neu tr a l a n d Ca tion ic Gr ou p 4 Meta l Com p ou n d s

Con ta in in g Octa m eth yld iben zotetr a a za a n n u len e

(Me₈ta a ^2-) Liga n d s. Syn th esis a n d Rea ctivity of

(Me₈ta a )MX₂a n d (Me₈ta a )MX⁺Com p lexes (M ) Zr , Hf;

X ) Cl, Hyd r oca r byl, NR₂, OR)

Alfredo Martin, Roger Uhrhammer, Thomas G. Gardner, and Richard F. J ordan*

Department of Chemistry, The University of Iowa, Iowa City, Iowa 52242

Robin D. Rogers

Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama 35487

Received September 15, 1997

The synthesis and reactivity of out-of-plane (Me₈taa)MX₂and (Me₈taa)MX⁺complexes (M)

Zr, Hf; X) Cl, hydrocarbyl, NR₂, OR) containing the dianionic tetraaza-macrocycle ligand

octamethyldibenzotetraazaannulene (Me₈taa^2-) are described. The reaction of [Li(Et₂O)]₂[Me₈-

taa] (1) with MCl₄(THF)₂yields (Me₈taa)MCl₂complexes (2a , M ) Zr; 2b, M ) Hf). Alkylation

of 2a ,b with LiCH₂SiMe₃or LiMe in hydrocarbon solvents yields (Me₈taa)M(CH₂SiMe₃)₂

(3a , M ) Zr; 4a , M ) Hf) or (Me₈taa)MMe₂(3b, M ) Zr; 4b, M ) Hf) complexes. Compound

3b rearranges by migration of a Me group from Zr to a Me₈taa imine carbon in coordinating

solvents. The reaction of (Me₈taa)H₂with the appropriate ZrR₄compound yields (Me₈taa)-

Zr(CH₂Ph)₂(3c) and (Me₈taa)Zr(CH₂CMe₃)₂(3d ). The reaction of (Me₈taa)H₂and Zr(NR₂)₄

yields (Me₈taa)Zr(NR₂)₂(6a , R ) Me; 6b, R ) Et). Spectroscopic data for (Me₈taa)MX₂

compounds 2, 3, 4, and 6 are consistent with cis, C_2v-symmetric structures. Dialkyl complexes

3 and 4 and bis(amide) complexes 6 react with chlorinated solvents (1,1,2,2-tetrachloroethane,

CH₂Cl₂) to yield 2. Compound 6a reacts with AlMe₃to afford the heterobimetallic µ-amido

complex [(Me₈taa)Zr(µ-NMe₂)₂AlMe₂][AlMe₄] (8), which does not undergo further reaction

to yield 3b. The reaction of dialkyl complexes 3 and 4a with HNR₃⁺reagents yields cationic

[(Me₈taa)MR][B(C₆F₅)₄] compounds (10a , M ) Zr, R ) η²-CH₂Ph; 10b, M ) Zr, R ) CH₂-

SiMe₃; 10c, M ) Zr, R ) CH₂CMe₃; 10d , M ) Hf, R ) Me). These species form labile adducts

with PMe₂Ph and THF. Cation 10a polymerizes ethylene to a linear polymer with low

activity, while 10d is unreactive with ethylene. 10a reacts with HOCMe₂CH₂CH₂CHdCH₂

to yield the mononuclear alkoxide complex (Me₈taa)Zr(OCMe₂CH₂CH₂CHdCH₂)⁺(13), in

which the pendant alkene is not coordinated. 10a also reacts with water or ethanol to yield

binuclear complexes [{(Me₈taa)Zr(µ-OR)}₂]²⁺(14a , R ) H; 14b, R ) Et). An X-ray structural

analysis of 14a reveals that one of the (Me₈taa)Zr units has an unusual inverted

conformation, and NMR data suggest that 14a ,b adopt similar structures in solution. 10d

reacts with 2-butyne to yield the double insertion product [(Me₈taa)Hf(CMedCMeCMedCMe₂)]⁺

(15) and with MeCtCSiMe₃to afford [(Me₈taa)Hf(C(SiMe₃)dCMe₂)]⁺(16), while 10a and

10b are unreactive with these alkynes. 10a and 10c react with terminal alkynes by

protonolysis to afford binuclear [{(Me₈taa)Zr(µ-CtCR)}₂]²⁺complexes (17a , R ) Ph; 17b, R

) Pr). Complex 17a reacts reversibly with PMe₃to yield the mononuclear cation (Me₈taa)-

Zr(CtCPh)(PMe₃)⁺(18a ). (Me₈taa)MR⁺species are less reactive for alkene and alkyne

insertion than are Cp₂MR⁺species.

In tr od u ction

(taa)MX₂structures with the large group 4 metal ions,

and steric interactions between the diiminato methyl

groups and the benzo rings enforce the saddle confor-

mation of the taa^2-ligand.⁵The molecular shape of

(taa)MX₂compounds is grossly similar to that of Cp₂-

MX₂bent metallocenes (C).⁶However, important dif-

Group 4 metal (taa)MX₂complexes containing diben-

zotetraazaannulene ligands (taa^2-, A, Chart 1) invari-

ably adopt cis, trigonal prismatic structures (B) in which

the metal is displaced out of the N₄-plane. In these

species, the taa^2-ligand adopts a saddle-shape confor-

mation and the benzo groups project toward the X

ligands.^1-4The small bonding pocket associated with

the 14-membered macrocycle precludes trans, in-plane

(1) (a) Yang, C.-H.; Ladd, J . A.; Goedken, V. L. J . Coord. Chem. 1988,

19, 235. (b) Yang, C.; Goedken, V. L. Inorg. Chim. Acta 1986, 117, L19.

(c) Goedken, V. L.; Ladd, J . A. J . Chem. Soc., Chem. Commun. 1982,

142.

Publication on Web 01/06/1998

Synthesis of (Me₈taa)MX₂and (Me₈taa)MX⁺Complexes

Organometallics, Vol. 17, No. 3, 1998 383

however, the N₄-ligation should make the (taa)M²⁺ion

Ch a r t 1

a harder Lewis acid than Cp₂M²⁺

.

The strong tendency for (taa)MX₂complexes to adopt

cis structures implies that five-coordinate (taa)MR⁺

alkyl complexes should form cis adducts (D) with Lewis

bases and organic substrates (L) and raises the pos-

sibility that such cations might display insertion and

σ-bond metathesis reactivity similar to that observed

for Cp₂MR⁺metallocene analogs.⁷As part of a program

aimed at the development of non-metallocene electro-

philic metal alkyl compounds, we initiated studies of

the chemistry of (taa)M(R)⁺cations to determine how

the structural and electronic differences between the

(taa)M²⁺and Cp₂M²⁺cores influence the comparative

reactivity of the corresponding cationic alkyls.^8,9In this

paper, we describe the synthesis and reactivity of a

series of neutral (Me₈taa)MX₂and cationic (Me₈taa)MX⁺

and (Me₈taa)MX(L)⁺complexes (X ) chloride, hydro-

carbyl, amide, alkoxide; L ) neutral Lewis base) con-

taining the octamethyltetraazaannulene ligand Me₈taa^2-

.

The parent macrocycle (Me₈taa)H₂is easily prepared by

Ni-templated condensation of 2,4-pentanedione and 4,5-

dimethyl-1,2-phenylenediamine, and the enhanced solu-

bility imparted by the aryl methyl substituents facili-

tates the study of cationic complexes.^10-12

Resu lts a n d Discu ssion

ferences between these classes of compounds exist,

which may be summarized as follows. (i) The X-M-X

angles in (taa)MX₂compounds (80-87°) are ca. 10°

smaller than those in Cp₂MX₂species;^6ahowever, the

taa^2-conformation can adjust somewhat to the steric/

electronic demands of the metal ion. (ii) The d⁰(taa)-

Syn th esis of (Me₈ta a )MR₂Com p lexes by An ion

Meta th esis. As illustrated in Scheme 1, double depro-

tonation of (Me₈taa)H₂with 2 equiv of MeLi in ether

yields the dilithium salt [Li(Et₂O)]₂[Me₈taa] (1), which

M

²⁺fragment has four low-lying empty metal d orbitals

(7) For reviews concerning the chemistry of cationic group 4 met-

allocene complexes, see: (a) Guram, A. S.; J ordan, R. F. In Compre-

hensive Organometallic Chemistry II; Abel, E. W., Stone, F. G. A.,

Wilkinson, G., Eds.; Elsevier: Oxford, 1995; Vol. 4, p 589. (b) Boch-

mann, M. J . Chem. Soc., Dalton Trans. 1996, 255. (c) Horton, A. D.

Trends Polym. Sci. 1994, 2, 158. (d) Marks, T. J . Acc. Chem. Res. 1992,

25, 57. (e) J ordan, R. F. Adv. Organomet. Chem. 1991, 32, 325. (f)

J ordan, R. F.; Bradley, P. K.; Lapointe, R. E.; Taylor, D. F. New J .

Chem. 1990, 14, 505.

(8) For a preliminary communication, see: Uhrhammer, R.; Black,

D. G.; Gardner, T. G.; Olsen, J . D.; J ordan, R. F. J . Am. Chem. Soc.

1993, 115, 8493.

(9) (a) Tjaden, E. B.; Swenson, D. C.; J ordan, R. F. Organometallics

1995, 14, 371. (b) Tjaden, E. B.; J ordan, R. F. Makromol. Chem.,

Macromol. Symp. 1995, 89, 231. (c) Bei, X.; Swenson, D. C.; J ordan,

R. F. Organometallics 1997, 16, 3282. (d) Tsukahara, T.; Swenson, D.

C.; J ordan, R. F. Organometallics 1997, 16, 3303. (e) Kim, I.; Nishihara,

Y.; J ordan, R. F.; Rogers, R. D.; Rheingold, A. L.; Yap, G. P. A.

Organometallics 1997, 16, 3314.

(z², xz, yz, x²- y²; see coordinate system in Chart 1)

and two low-lying empty orbitals localized on the taa

imine carbons, while the Cp₂M²⁺ion has three empty

metal-based frontier orbitals which are localized in the

equatorial plane between the Cp ligands.^6b(iii) The

(taa)M²⁺ion can coordinate four additional ligands, as

demonstrated by the formation of (taa)₂M sandwich

complexes,^2bwhile Cp₂M²⁺can accommodate only three

additional ligands. (iv) On the basis of computed metal

charges and electrophilicity indices, the metal center in

(taa)M²⁺is less electrophilic than that in Cp₂M^{2+ 2e}

;

(2) (a) Floriani, C.; Curli, S.; Chiesi-Villa, A.; Guastini, C. Angew.

Chem., Int. Ed. Engl. 1987, 26, 70. (b) De Angelis, S.; Solari, E.; Gallo,

E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Inorg. Chem. 1992, 31, 2520.

(c) Giannini, L.; Chiesi-Villa, A.; Rizoli, C. Angew. Chem., Int. Ed. Engl.

1994, 33, 2204. (d) Cozzi, P. G.; Floriani, C.; Chiesi-Villa, A.; Rizzoli,

C. Synlett 1994, 857. (e) Giannini, L.; Solari, E.; De Angelis, S.; Ward,

T. R.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J . Am. Chem. Soc. 1995,

117, 5801.

(3) (a) Housmekerides, C. E.; Ramage, D. L.; Kretz, C. M.; Shontz,

J . T.; Pilato, R. S.; Geoffroy, G. L.; Rheingold, A. L.; Haggerty, B. S.

Inorg. Chem. 1992, 31, 4453. (b) Nikonov, G. I.; Blake, A. J .; Mountford,

P. Inorg. Chem. 1997, 36, 1107. (c) Dunn, S. C.; Batsanov, A. S.;

Mountford, P. J . J . Chem. Soc., Chem. Commun. 1994, 2007. (d)

Mountford, P.; Swallow, D. J . Chem. Soc., Chem. Commun. 1995, 2357.

(e) Blake, A. J .; Mountford, P.; Nikonov, G. I.; Swallow, D. J . Chem.

Soc., Chem. Commun. 1996, 1835.

(4) Cotton, F. A.; Czuchajowska, J . Polyhedron 1990, 21, 2553.

(5) (a) The ideal M-N distance for an in-plane (taa)MX_nstructure

is 1.86 Å, see: Weiss, M. C.; Bursten, B.; Peng, S.-M.; Goedken, V. L.

J . Am. Chem. Soc. 1976, 98, 8021. (b) Goedken, V. L.; Pluth, J . J .;

Peng, S.-M.; Bursten, B. J . Am. Chem. Soc. 1976, 98, 8014.

(6) (a) Cardin, D. J .; Lappert, M. F.; Raston, C. L. Chemistry of

Organo-Zirconium and -Hafnium Compounds; Halsted Press: New

York, 1986; Chapter 4. (b) Lauher, J . W.; Hoffmann, R. J . Am. Chem.

Soc. 1976, 98, 3389.

(10) (a) Place, D. A.; Ferrara, G. P.; Harlond, J . J .; Dabrowiak, J .

C. J . Heterocyclic Chem. 1980, 17, 439. (b) Cutler, A. R.; Alleyne, C.

S.; Dolphin, D. Inorg. Chem. 1985, 24, 2276. (c) Goedken, V. L.; Weiss,

M. C. Inorg. Synth. 1980, 20, 115.

(11) For related work concerning group 4 metal porphyrin com-

plexes, see: (a) Brand, H.; Capriotti, J . A.; Arnold, J . Organometallics

1994, 13, 4469. (b) Brand, H.; Arnold, J . Organometallics 1993, 12,

3655. (c) Arnold, J .; J ohnson, S. E.; Knobler, C. B.; Hawthorne, M. F.

J . Am. Chem. Soc. 1992, 114, 3996. (d) Brand, H.; Arnold, J . J . Am.

Chem. Soc. 1992, 114, 2266. (e) Brand, H.; Arnold, J . Angew. Chem.,

Int. Ed. Engl. 1994, 33, 95. (f) Shibata, K.; Aida, J .; Inoue, S.

Tetrahedron Lett. 1992, 33, 1077. (g) Shibata, K.; Aida, T.; Inoue, S.

Chem. Lett. 1992, 1173. (h) Woo, L. K.; Hays, J . A.; J acobson, R. A;

Day, C. L. Organometallics 1991, 10, 2102. (i) Latour, J .; Boreham, C.

J .; Marchon, J . J . Organomet. Chem. 1990, 190, C61. (j) Ryu, S.;

Whang, D.; Kim, J .; Yeo, W.; Kim, K. J . Chem. Soc., Dalton Trans.

1993, 205. (k) Kim, H.-J .; Whang, D.; Kim, K.; Do, Y. Inorg. Chem.

1993, 32, 360. (l) Kim, H.-J .; Whang, D.; Do, Y.; Kim, K. Chem. Lett.

1993, 807. (m) Kim, K.; Lee, W. S.; Kim, H.-J .; Cho, S.-H.; Girolami,

G. S.; Gorlin, P. A.; Suslick, K. S. Inorg. Chem. 1991, 30, 2652.

(12) For related work concerning group 4 metal (Me₄taen)MX₂

complexes, see: (a) Black, D. G.; Swenson, D. C.; J ordan, R. F.; Rogers,

R. D.Organometallics 1995, 14, 3539. (b) Black, D. G.; J ordan, R. F.;

Rogers, R. D. Inorg. Chem. 1997, 36, 103.

384 Organometallics, Vol. 17, No. 3, 1998

Martin et al.

Sch em e 1

80% isolated yield (Scheme 1). Metal-to-ligand methyl

migration is not observed for 4b at ambient tempera-

ture.

Syn th esis of (Me₈ta a )MR₂Com p lexes by Alk a n e

Elim in a tion . The reaction of a slurry of (Me₈taa)H₂

and Zr(CH₂Ph)₄in pentane at 23 °C affords dibenzyl

complex 3c, which is insoluble in pentane and can be

isolated in 95% yield by simple filtration (eq 2). The

can be isolated as a purple solid. The reaction of 1 with

MCl₄(THF)₂(M ) Zr, Hf) in THF at 23 °C yields the

dichloride complexes (Me₈taa)MCl₂(2a , M ) Zr; 2b, M

) Hf). These complexes can be isolated as yellow solids

and are soluble in chlorinated solvents, but only spar-

ingly soluble in benzene or toluene. The ¹H and ¹³C

NMR spectra of 2a ,b are consistent with cis C_2v-

symmetric structures analogous to those observed for

(Me₄taa)MX₂compounds (B).^2a,e

The reaction of 2a with 2 equiv of LiCH₂SiMe₃in

pentane/toluene at 23 °C affords (Me₈taa)Zr(CH₂SiMe₃)₂

(3a ), which is isolated in good yield as a toluene solvate

(Scheme 1). The reaction of 2a with solid MeLi in

toluene at low temperature affords (Me₈taa)ZrMe₂(3b),

which is isolated in low (15%) yield. Attempts to

improve the yield of 3b or isolate other reaction products

by varying the reaction conditions were unsuccessful.

Attempts to prepare 3b using other methylating agents

were also unsuccessful.¹³The poor yield of 3b most

likely results from facile migration of the methyl group

to an electrophilic Me₈taa imine carbon. This process

is promoted by Lewis bases, and thus, the synthesis of

3b is successful only in noncoordinating media. For

example, the reaction of 2a with MeLi in Et₂O at low

temperature yields the ligand-alkylation product (Me₉-

taa)ZrMe(OEt₂) (5, eq 1). Isolated 3b reacts with THF

to yield a similar product. Metal-to-ligand alkyl migra-

tions in (Me₄taa)ZrR₂compounds have been studied in

detail by Floriani,^2a,eand similar reactions have been

noted for (Me₄taen)ZrR₂compounds.¹²

reaction of (Me₈taa)H₂and Zr(CH₂CMe₃)₄requires more

vigorous conditions (toluene, 50 °C, 5 days) due to the

increased steric requirements of the neopentyl ligand

but affords bis(neopentyl) complex 3d in 43% isolated

yield. Complex 3d can also be prepared by alkylation

of 2a with LiCH₂CMe₃, but in lower yield (21%).

Ch em ical P r oper ties of (Me₈taa)MR₂Com pou n ds.

The (trimethylsilyl)methyl and neopentyl complexes 3a ,

3d , and 4a are soluble in benzene and toluene, but the

methyl and benzyl complexes 3b, 3c, and 4b are only

sparingly soluble in these solvents. All of these com-

plexes are soluble in chlorinated solvents, in which they

slowly decompose to the parent dichlorides 2a and 2b.

For example, 4b reacts with 1,1,2,2-tetrachloroethane-

d₂(C₂D₂Cl₄) within 12 h at 23 °C to yield 2b and

methane-d₁as the only NMR-detectable products (eq

3). Compound 3a reacts with C₂D₂Cl₄more slowly, but

The reaction of 2b with LiCH₂SiMe₃or MeLi in

benzene or toluene (23 °C) affords (Me₈taa)HfR₂com-

plexes 4a (R ) CH₂SiMe₃) and 4b (R ) CH₃) in 60-

after 8 days at 23 °C it is converted to a 2:1 mixture of

2a and (Me₈taa)Zr(CH₂SiMe₃)Cl; SiMe₄-d₁is also de-

tected.

Sp ectr oscop ic P r op er ties of (Me₈ta a )MR₂Com -

p ou n d s. The ¹H and ¹³C NMR spectra of 3a -d and

4a ,b are consistent with cis C_2v-symmetric structures

(13) (Me₈taa)ZrCl₂forms an adduct with AlMe₃, reacts with MgMe₂

to yield uncharacterized products, and does not react with SnMe₄or

HgMe₂.

Synthesis of (Me₈taa)MX₂and (Me₈taa)MX⁺Complexes

Organometallics, Vol. 17, No. 3, 1998 385

analogous to those observed for (Me₄taa)Zr(CH₂Ph)₂.^2a

In each case, one benzo-Me, one benzo-H, one diiminato-

Me, and one diiminato-CH resonance are observed for

the Me₈taa^2-ligand, and a single set of hydrocarbyl

resonances is observed. The MCH₂R J _CHvalues are

quite low, ranging from 100 Hz for (Me₈taa)Hf(CH₂-

SiMe₃)₂(4a ) to 119 Hz for (Me₈taa)Zr(CH₂Ph)₂(3c),

which is characteristic of hydrocarbyl groups bound to

electropositive metal centers.¹⁴The Zr-CH₃J _CHvalue

for 3b (111 Hz) is smaller than that for Cp₂ZrMe₂(118

Hz), which implies that the (Me₈taa)Zr fragment is

effectively more electropositive than the Cp₂Zr frag-

ment, or in other words, the Zr-C bonding in the former

compound is more ionic than that in the latter.^15,16This

is consistent with the rapid solvolysis noted above for

the (Me₈taa)MR₂compounds in chlorinated solvents.

Note that there is no evidence for agostic interactions

in Cp₂ZrMe₂from X-ray crystallographic studies or

NMR studies of the partially deuterated derivative Cp₂-

Zr(CH₂D)₂,¹⁷and X-ray structural and NMR data for

(Me₄taa)Zr(CH₂Ph)₂and (Me₄taen)Zr(CH₂Ph)₂reveal

normal undistorted benzyl ligands,^2a,12awhich suggests

that agostic interactions are unlikely to be present in

(Me₈taa)ZrMe₂. Therefore, the difference in the J _CH

values of Cp₂ZrMe₂and (Me₈taa)ZrMe₂is probably not

influenced by agostic interactions.¹⁸The ZrCH₂Ph J _CH

value for 3c (119 Hz) is consistent with normal η¹-benzyl

bonding.¹⁹

Sch em e 2

plexes rac-(EBI)Zr(NMe₂)₂and rac-(SBI)Zr(NMe₂)₂, which

are converted to the corresponding dimethyl complexes

and {AlMe₂(µ-NMe₂)}₂by reaction with 4 equiv of

AlMe₃.²¹We investigated the synthesis of (Me₈taa)Zr-

(NR₂)₂complexes and their utility as possible precursors

to 3b, which, as noted above, is difficult to prepare by

salt elimination.

The reaction of (Me₈taa)H₂and Zr(NMe₂)₄in toluene

(1 h, 23 °C) affords (Me₈taa)Zr(NMe₂)₂(6a ), which is

isolated as a red powder in 90% yield by crystallization

from toluene/pentane at -40 °C (eq 4). Bis(diethyla-

Syn t h esis a n d P r op er t ies of (Me₈t a a )Zr (NR ₂)₂

Com p lexes. Group 4 metal amide complexes are

readily prepared by amine-elimination reactions of

M(NR₂)₄compounds and sufficiently acidic ligand re-

agents and are useful intermediates in the synthesis

of other derivatives.²⁰For example, the reaction of

Zr(NMe₂)₄and 1,2-bis(indenyl)ethane ((EBI)H₂) or

Me₂(indenyl)₂Si ((SBI)H₂) yields the metallocene com-

mido) analog 6b is prepared in a similar fashion by the

reaction of (Me₈taa)H₂and Zr(NEt₂)₄, but in this case

more vigorous reaction conditions are required (toluene,

48 h, 60 °C) due to the increased steric crowding in the

starting metal amide compound. NMR data for 6a ,b

are consistent with cis C_2v-symmetric structures.

Complexes 6a ,b are soluble in benzene but insoluble

in aliphatic solvents, and react with CH₂Cl₂ultimately

yielding 2a . The reaction of 6a with CD₂Cl₂was

(14) For leading references, see ref 9a and (a) Thompson, M. E.;

Baxter, S. M.; Bulls, A. R.; Burger, B.; Nolan, M. C.; Santarsiero, B.

D.; Schaefer, W. P.; Bercaw, J . E. J . Am. Chem. Soc. 1987, 109, 203.

(15) Finch, W. C.; Anslyn, E. V.; Grubbs, R. H. J . Am. Chem. Soc.

1988, 110, 2406.

(16) Detailed comparisons of J _CHvalues for MCH₂CMe₃, MCH₂-

SiMe₃, and MCH₂Ph compounds are complicated by steric effects and

the possibility of weak M- - -Ph interactions, which can strongly

influence M-C-C angles and, consequently, the J _CHvalues, see: Guo,

Z.; Swenson, D. C.; J ordan, R. F. Organometallics 1994, 13, 1424 and

references therein.

1

monitored by H NMR spectroscopy (Scheme 2). Com-

plex 6a is cleanly (>90%) converted to (Me₈taa)Zr(Cl)-

(NMe₂) (7) and 0.5 equiv of CD₂(NMe₂)₂within 5 h at

23 °C in CD₂Cl₂solution. After an additional 14 h, 7 is

completely transformed into 2a , and a second 0.5 equiv

of CD₂(NMe₂)₂is formed. In a parallel experiment, 6a

was reacted with CH₂Cl₂under the same conditions.

The volatiles were removed by vacuum distillation (and

trapped) to afford 2a in 93% isolated yield. ¹H and ¹³C

NMR spectra and mass spectral analysis of the volatiles

established the presence of CH₂(NMe₂)₂as the sole

NMe₂-containing product.

While the mechanistic details of the reaction of 6a

with CH₂Cl₂are unknown, this reaction clearly involves

nucleophilic displacement of chloride from CH₂Cl₂by

the metal amide, which may occur by formation of an

intermediate solvent adduct. The expected initial or-

(17) (a) Hunter, W. E.; Hrncir, D. C.; Bynum, R. V.; Penttila, R. A.;

Atwood, J . L. Organometallics 1983, 2, 750. (b) Green, M. L. H.;

Hughes, A. K.; Popham, N. A.; Stephens, A. H. D.; Wong, L.-L. J . Chem.

Soc., Dalton Trans. 1992, 3077.

(18) For agostic interactions, see: (a) Brookhart, M.; Green, M. L.

H.; Wong, L. Prog. Inorg. Chem. 1988, 36, 1. (b) Crabtree, R. H.;

Hamilton, D. G. Adv. Organomet. Chem. 1988, 28, 299. (c) Ginzburg,

A. S. Russ. Chem. Rev. 1988, 57, 1175. (d) Cotton, F. A.; Luck, R. L.

Inorg. Chem. 1989, 28, 3210. (e) Dawoodi, Z.; Green, M. L. H.; Mtetwa,

V. S. B.; Prout, K.; Schultz, A. J .; Williams, J . M.; Koetzle, T. F. J .

Chem. Soc., Dalton Trans. 1986, 1629.

(19) For discussions of ηⁿ-benzyl bonding see ref 9c and references

therein.

(20) For reviews and selected examples, see: (a) Lappert, M. F.;

Power, P. P.; Sanger, A. R.; Srivastava, R. C. Metal and Metalloid

Amides; Ellis Horwood: Chichester, West Sussex, 1980. (b) Bradley,

D. C. Adv. Inorg. Chem. Radiochem. 1972, 15, 259. (c) Bradley, D. C.;

Chisholm, M. H. Acc. Chem. Res. 1976, 9, 273. (d) Bowen, D. E.; J ordan,

R. F.; Rogers, R. D. Organometallics 1995, 14, 3630. (e) Duan, Z.;

Verkade, J . G. Inorg. Chem. 1995, 34, 4311. (f) Galakhov, M.; Martin,

A.; Mena, M.; Yelamos, C. J . Organomet. Chem. 1995, 496, 217. (g)

Hughes, A. K.; Meetsama, A.; Teuben, J . H. Organometallics 1993,

12, 1936. (h) Bu¨rger, H.; Da¨mmgen, U. J . Organomet. Chem. 1975,

101, 295. (i) Da¨mmgen, U.; Bu¨rger, H.; J . Organomet. Chem. 1975,

101, 307. (j) J enkins, A. D.; Lappert, M. F.; Srivastava, A. C. J .

Organomet. Chem. 1970, 23, 165. (k) Chandra, G.; Lappert, M. F. J .

Chem. Soc. A 1968, 1940.

(21) (a) Diamond, G. M.; J ordan, R. F.; Petersen, J . L. J . Am. Chem.

Soc. 1996, 118, 8024. (b) Christopher, J . N.; Diamond, G. M.; J ordan,

R. F.; Petersen, J . L. Organometallics 1996,15, 4038. (c) Kim, I.; J ordan,

R. F. Macromolecules 1996, 29, 489.

386 Organometallics, Vol. 17, No. 3, 1998

Martin et al.

the ¹³C NMR spectrum.²⁴The presence of the AlMe₄

-

Sch em e 3

anion was confirmed by the reaction of 8 with 1 equiv

of the noncoordinating acid [HNMePh₂][B(C₆F₅)₄] (CD₂-

Cl₂, 23 °C, NMR scale), which yields the ion-exchange

product 9, methane, Al₂Me₆, and NMePh₂. The ¹H

NMR spectrum of 9 is identical to that of 8, with the

exception of the anion resonances.

The formation of 8 from the reaction of AlMe₃and 6a

is reminiscent of reactions of AlX₃compounds (X )

halide, alkyl, etc.) with Lewis bases, which in many

cases yield [L_mAlX₂][AlX₄] (m ) 2-5) salts.²⁵Thus, 6a

may be viewed as a bidentate Lewis base in Scheme 3,

a description which underscores the high nucleophilicity

of the amide groups noted above. The retention of the

Zr-N bonds in the formation of 8 contrasts with the

complete amide/methyl exchange observed in reactions

21,22

of Cp₂Zr(NMe₂)₂compounds with AlMe₃

and sug-

gests that the (Me₈taa)Zr²⁺unit is a harder Lewis acid

than the Cp₂Zr²⁺unit.

Syn t h esis of Lew is-Ba se-F r ee [(Me₈t a a )MR ]-

[B(C₆F ₅)₄] Com p lexes. Cationic complexes 10 are

formed by protonolysis of 3 and 4, using either [HNMe₂-

Ph][B(C₆F₅)₄] or [HNMePh₂][B(C₆F₅)₄] (eq 5).²⁶These

reactions are complete within minutes at 23 °C in

chlorinated or aromatic solvents and afford 10a -d in

80-100% NMR yield. Compounds 10a -d are soluble

in chlorinated solvents but separate as oils from aro-

matic solvents. Compounds 10a and 10c were isolated

from the reaction mixtures as solid benzene or toluene

solvates by removal of the volatiles under vacuum,

washing with benzene or toluene to remove the amine

coproduct, and vacuum drying. Complexes 10b and 10d

were generated in situ and characterized by NMR.

The ¹H and ¹³C NMR spectra of 10a (CD₂Cl₂) are

unchanged between 23 and -90 °C and establish that

this species has effective C_2vsymmetry. The ¹H and

¹³C NMR data also establish that the benzyl ligand is

coordinated in an η²-fashion, as observed for other

coordinatively unsaturated early metal benzyl species.^9c,d

ganic product, CH₂(NMe₂)Cl, must be more reactive

than CH₂Cl₂toward 6a , since it was not observed as

an intermediate. The high reactivity of 6a with CH₂-

Cl₂contrasts with the stability of Cp₂M(NR₂)₂com-

pounds in this solvent and indicates that the amide

ligands in (Me₈taa)Zr(NR₂)₂compounds are highly nu-

cleophilic.²²This is consistent with the suggestion made

above that the (Me₈taa)MX₂systems are more ionic than

the analogous metallocene complexes.

Rea ction of (Me₈ta a )Zr (NMe₂)₂a n d AlMe₃. Com-

plex 6a reacts with 1 equiv of Al₂Me₆in benzene at 23

°C to yield the unusual hetero-dinuclear µ-amido salt

[(Me₈taa)Zr(µ-NMe₂)₂AlMe₂][AlMe₄] (8), which precipi-

tates as a yellow solid and is isolated by filtration

(Scheme 3). Compound 8 does not react further with

excess Al₂Me₆, even at 65 °C in benzene, and is soluble

and stable in CH₂Cl₂and Et₂O.

The structural assignment for 8 is based on NMR

spectral data, elemental analysis, and reactivity data.

The NMR spectra establish the presence of a C_2v-

symmetric (Me₈taa)Zr unit, two symmetric NMe₂groups

(¹³C NMR δ 44.1, qq, J _CH) 134, 6 Hz), and a symmetric

AlMe₂unit (¹H NMR δ -1.72 , s, 6H; ¹³C NMR δ -14.6,

br q, J _CH) 111 Hz) in the cation of 8. These data do

not conclusively allow differentiation between the µ-NMe₂

or µ-Me structures, but the proposed structure is the

most reasonable given the general preference for amide

groups rather than alkyl groups to occupy bridging

positions in [AlR₂(NR₂′ )]₂compounds.²³The NMR

spectra of 8 also contain characteristic resonances for

the free AlMe₄^-anion; i.e., a 1:1:1:1:1:1 sextet (δ -1.22,

J _Al-H) 6.3 Hz) which integrates for 12 H is observed

in the ¹H NMR spectrum, and an 18 line pattern (δ

-5.2, J _Al-C) 71.2 Hz, J _C-H) 106.5 Hz) is observed in

(24) (a) For the ¹H NMR spectrum of AlMe₄^-, see: Oliver, J . P.;

Wilkie, C. A. J . Am. Chem. Soc. 1967, 89, 104. (b) A 24-line pattern is

expected for the ¹³C NMR spectrum of AlMe₄^-, but several resonances

overlap. The observed spectrum closely matched a simulated spectrum

generated using the J _Al-Cand J _C-Hvalues quoted in the text, which

are in agreement with those reported in Yamamoto, O. Chem. Lett.

1975, 511.

(25) (a) Lehmkuhl, H.; Eisenbach, W. J ustus Liebigs Ann. Chem.

1967, 705, 42. (b) Lehmkuhl, H.; Kobs, H.-D. J ustus Liebigs Ann. Chem.

1968, 719, 11. (c) Bott, S. G.; Elgamal, H.; Atwood, J . L. J . Am. Chem.

Soc. 1985, 107, 1796. (d) Engelhardt, L. M.; Kynast, U.; Raston, C. L.;

White, A. H. Angew. Chem., Int. Ed. Engl. 1987, 26, 681. (e) Means,

N. C.; Means, C. M.; Bott, S. G.; Atwood, J . L. Inorg. Chem. 1987, 26,

1466. (f) Bott, S. G.; Alvanipour, A.; Morley, S. D.; Atwood, D. A.;

Means, C. M.; Coleman, A. W.; Atwood, J . L. Angew. Chem., Int. Ed.

Engl. 1987, 26, 485. (g) Richey, H. G., J r.; BergStresser, G. L.

Organometallics 1988, 7, 1459. (h) Sangokoya, S. A.; Moise, F.;

Pennington, W. T.; Self, M. F.; Robinson, G. H. Organometallics 1989,

8, 2584. (i) Self, M. F.; Pennington, W. T.; Laske, J . A.; Robinson, G.

H. Organometallics 1991, 10, 36. (j) Atwood, J . L.; Robinson, K. D.;

J ones, C.; Raston, C. L. J . Chem. Soc., Chem. Commun. 1991, 1697.

(k) Uhl, W.; Wagner, J .; Fenske, D.; Baum, G. Z. Anorg. Allg. Chem.

1992, 612, 25. (l) Emig, N.; Re´au, R.; Krautscheid, H.; Fenske, D.;

Bertrand, G. J . Am. Chem. Soc. 1996, 118, 5822. (m) J egier, J . A.;

Atwood, D. A. Inorg. Chem. 1997, 36, 2034. (n) Atwood, D. A. ; J egier,

J . J . Chem. Soc., Chem. Commun. 1996, 1507.

(22) See ref 21 and (a) Diamond, G. M.; J ordan, R. F.; Petersen, J .

L. Organometallics 1996, 15, 4045. (b) Diamond, G. M.; J ordan, R. F.;

Petersen, J . L. Organometallics 1996, 15, 4030.

(23) (a) McLaughlin, G. M.; Sim, G. A.; Smith, J . D. J . Chem. Soc.,

Dalton Trans. 1972, 2197. (b) Al-Wassil, A. I.; Hitchcock, P. B.;

Sarisaban, S.; Smith, J . D.; Wilson, C. L. J . Chem. Soc., Dalton Trans.

1985, 1929. (c) Interrante, L. V.; Sigel, G. A.; Garbauskas, M.; Hejma,

C.; Slack, G. A. Inorg. Chem. 1989, 28, 252. (d) Sauls, F. C.; Czekaj,

C. L.; Interrante, L. V. Inorg. Chem. 1990, 29, 4688. (e) Vahrenkamp,

H.; No¨th, H. J . Organomet. Chem. 1968, 12, 281. (f) Amero, B. A.;

Schram, E. P. Inorg. Chem. 1976, 15, 2842.

(26) (a) Turner, H. W.; Hlatky, G. G. Eur. Pat. Appl. 0 277 004, 1988.

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

1989, 111, 2728. (c) Hlatky, G. G.; Eckman, R. R.; Turner, H. W.

Organometallics 1992, 111, 1413. (d) Bochmann, M.; Wilson, L. M. J .

Chem. Soc., Chem. Commun. 1986, 1610. (e) Bochmann, M.; Lancaster,

S. J . Organometallics 1993, 12, 633. (f) Lin, Z.; Le Marechal, J .; Sabat,

M.; Marks, T. J . J . Am. Chem. Soc. 1987, 109, 4127. (g) Yang, X.; Stern,

C. L.; Marks, T. J . Organometallics 1991, 10, 840.

Synthesis of (Me₈taa)MX₂and (Me₈taa)MX⁺Complexes

Organometallics, Vol. 17, No. 3, 1998 387

1

metry and do not contain the expected J _PHor J _PC

couplings between the phosphine and alkyl ligands,

indicating that PMe₂Ph exchange is rapid on the NMR

time scale. The labile THF adduct 11b is generated by

protonolysis of 3a in the presence of THF.

The ortho-Ph H NMR resonance appears at high field

(δ 5.01), and the ZrCH₂Ph J _CHvalue (136 Hz) is large,

characteristic of an acute Zr-C-Ph angle. The benzyl

ligand is probably less distorted than that in Cp₂Zr(η²-

CH₂Ph)(NCMe)⁺, for which a larger J _CHvalue (145 Hz)

was observed.²⁷The ¹⁹F NMR spectrum of 10a contains

The reaction of base-free benzyl complex 10a with

THF (CD₂Cl₂, 23 °C), results in clean formation of the

THF adduct [(Me₈taa)Zr(CH₂Ph)(THF)][B(C₆F₅)₄] (11c).

The low-temperature (-80 °C) ¹H NMR spectrum of 11c

contains two benzo-H, two diiminato-CH, four methyl

resonances, one set of benzyl resonances, and signals

for coordinated THF. This spectrum is consistent with

a C_s-symmetric structure in which the THF and benzyl

ligands are oriented over the diiminato sectors of the

Me₈taa ligand, i.e., a trigonal-prismatic structure analo-

gous to those observed for (Me₄taa)ZrX₂compounds.^2a,e

The chemical shift of the benzyl ortho hydrogens (δ 6.07)

is similar to that of (Me₈taa)Zr(CH₂Ph)₂(δ 6.39) and

far downfield from that of (Me₈taa)Zr(η²-CH₂Ph)⁺(10a ,

δ 5.01), which indicates that the benzyl ligand is not

significantly distorted.^9c,dComplex 11c undergoes rapid

intermolecular THF exchange at ambient temperature;

however, addition of excess THF does not shift the

resonances for 11c, which indicates that a bis(THF)

adduct is not formed. The labile THF adduct (Me₈taa)-

Hf(Me)(THF)⁺(11d ) is generated by addition of THF

to 10d .

-

resonances for free B(C₆F₅)₄and is unchanged down

to -90 °C, and there is no evidence for solvent coordina-

tion from low-temperature ¹³C NMR experiments.²⁸

Collectively, the NMR data for 10a are consistent with

a base-free η²-benzyl structure and rapid rotation

around the Zr-C bond (even at low temperature).

The NMR spectra of 10b-d imply that these species

also have C_2vsymmetry on the NMR time scale at

ambient temperature and, for 10c, -90 °C. The hydro-

carbyl ligands probably project out along the C₂axis of

the (Me₈taa)Zr unit (cf. (Me₄taa)TidO);^3ahowever, the

NMR data are also consistent with fluxional C_s-sym-

metric structures in which the hydrocarbyl ligands

exchange rapidly between the two lateral coordination

1

sites. The MCH₂R H NMR resonances are shifted to

higher field and the MCH₂R ¹³C NMR resonances are

shifted to lower field versus the corresponding reso-

nances for the neutral precursors. The ZrCH₂R J _CH

value for 10b,c (107 Hz) is similar to the values

observed for the corresponding neutral dialkyls. While

detailed studies of the solution structures of these

cations were not pursued, the available data indicate

that agostic interactions and solvent or anion interac-

tions are weak at best.

R ea ct ivit y of (Me₈t a a )M(R )⁺Com p lexes w it h

Eth ylen e. Isolated salt 10a is a low-activity ethylene

polymerization catalyst. At 50 °C (toluene, 1.3 atm of

ethylene), 10a produces linear polyethylene of moderate

molecular weight (M_w) 99 300) and narrow molecular

weight distribution (M_w/M_n) 2.6), with a minimum

activity of 300 (g of PE)(mol of cat.)^-1atm^-1h^-1; the

activity was slightly higher in the presence of Al(ⁱBu)₃

added as a scavenger (550 (g of PE)(mol of cat.)^-1atm^-1

h^-1). The activity of 10a is ca. 100 times lower than

that measured for Cp₂ZrMe₂/[HNMePh₂][B(C₆F₅)₄]/Al(ⁱ-

Bu)₃under the same conditions (g48 000 (g of PE)(mol

of cat.)^-1atm^-1h^-1). The reaction of 10a with ethylene

(1 atm) at 90 °C in chlorobenzene with Al(ⁱBu)₃added

as scavenger produced very low molecular weight linear

polyethylene (M_w) 1,410, M_w/M_n) 1.8). NMR analysis

of this polymer established that the ratio of saturated

end groups/vinyl end groups is 13/1, suggesting that

chain transfer to aluminum is the predominant chain-

transfer process under these conditions. Benzyl end

groups were not detected in any of the polyethylene

Gen er a tion of Lew is-Ba se-Sta bilized (Me₈ta a )M-

(R)(L)⁺Sp ecies. Base-free (Me₈taa)M(R)⁺cations form

isolable Lewis-base adducts (eq 6). The reaction of 3a

with [HNBu₃][BPh₄] and 1 equiv of PMe₂Ph (C₂H₄Cl₂,

23 °C) affords [(Me₈taa)Zr(CH₂SiMe₃)(PMe₂Ph)][BPh₄]

(11a ), which can be isolated as a yellow solid in 77%

yield. The H and ¹³C NMR spectra (CD₂Cl₂, 23 °C) of

11a establish that this species has effective C_2vsym-

1

(27) J ordan, R. F.; LaPointe, R. E.; Bajgur, C. S.; Echols, S. F.;

Willett, R. D. J . Am. Chem. Soc. 1987, 109, 4111.

(28) The possibility of solvent coordination was probed by low-

temperature ¹³C NMR studies of a solution of 10a in a 1:1 mixture of

CH₂Cl₂and CD₂Cl₂. No resonances attributable to coordinated CH₂-

Cl₂were observed at -80 °C, which indicates that solvent is either

not coordinated, or that exchange of coordinated and free solvent is

rapid at this temperature. See: (a) Ferna´ndez, J .; Gladysz, J . A.

Organometallics 1989, 8, 207. (b) Huang, D.; Huffman, J . C.; Bollinger,

J . C.; Eisenstein, O.; Caulton, K. G. J . Am. Chem. Soc. 1997, 119, 7398.

(c) Kulawiec, R. J .; Crabtree, R. H. Coord. Chem. Rev. 1990, 99, 89

and references therein.

388 Organometallics, Vol. 17, No. 3, 1998

Martin et al.

samples produced by 10a . NMR monitoring of ethylene

polymerization by 10a revealed the disappearance of

10a and formation of polyethylene, but intermediate

(Me₈taa)Zr(R)⁺species (R ) growing chain) were not

detected. The cationic hafnium methyl complex 10d

does not polymerize ethylene under conditions similar

to those discussed above for 10a .

Syn t h esis a n d St r u ct u r e of (Me₈t a a )Zr (η¹-OC-

Me₂CH₂CH₂CHdCH₂)⁺. One possible reason for the

low reactivity of (Me₈taa)M(R)⁺species with ethylene

is that these cations are insufficiently electrophilic to

efficiently coordinate and activate olefins. To probe this

possibility, we investigated the reaction of 10a with the

alcohol HOCMe₂CH₂CH₂CHdCH₂(12), which contains

a pendant olefin group. We previously showed that

(C₅R₅)₂Zr(η²-O,C¹-OCMe₂CH₂CH₂CHdCH₂)⁺complexes

((C₅R₅)₂) Cp₂, rac-EBI), which contain the alkoxide

ligand derived from 12, coordinate the pendant olefin

in preference to CD₂Cl₂, MeB(C₆F₅)₃^-, or B(C₆F₅)₄

.

- 29

Benzyl cation 10a reacts rapidly with 12 at 23 °C in

CH₂Cl₂or benzene to yield the cationic alkoxide complex

(Me₈taa)Zr(η¹-OCMe₂CH₂CH₂CHdCH₂)⁺(13), which is

F igu r e 1. Structure of the {(Me₈taa)Zr(µ-OH)}₂²⁺Cation

of 14a .

1

isolated as a yellow solid (eq 7). The H and ¹³C NMR

hydroxy and ethoxy complexes 14a and 14b, which are

isolated as yellow solids after crystallization from CH₂-

Cl₂/pentane (eq 8).

data for the olefin group of 13 are unchanged from data

for 12, indicating that the pendant olefin is not coordi-

nated in this species. In contrast, large coordination

shifts are observed for the olefinic resonances in (C₅R₅)₂-

The structure of 14a ‚pentane was determined by a

single-crystal X-ray diffraction analysis of the pentane

solvate (Table 1). Compound 14a ‚pentane crystallizes

1

Zr(η²-O,C¹-OCMe₂CH₂CH₂CHdCH₂)⁺species. The H

2+

-

as discrete {(Me₈taa)Zr(µ-OH)}₂and B(C₆F₅)₄ions.

The structure of the cation is shown in Figure 1, and

selected bond distances and angles are listed in Table

2. The cation structure consists of two (Me₈taa)Zr units

linked by two symmetrical hydroxide bridges. One (Me₈-

taa)Zr unit (Zr1) adopts the normal saddle conformation

with trigonal-bipyramidal geometry around Zr (see B

in Chart 1). The Zr(1)-N bond distances (average )

2.16(3) Å) and the Zr(1)-N₄plane displacement (1.034(5)

Å) are similar to those observed for (Me₄taa)ZrCl₂

(average Zr-N ) 2.166(5) Å; Zr-N₄) 1.071(2) Å) and

(Me₄taa)Zr(CH₂Ph)₂(average Zr-N ) 2.190(8) Å; Zr-

N₄) 1.019(2) Å).^2a,b,eThe angle between the benzo

planes (50.8(3)°) and the angle between the diiminato

planes (73.5(4)°), which define the shape of the saddle

are also quite normal. In contrast, the second (Me₈taa)-

Zr unit of 14a (Zr2) adopts an unusual inverted confor-

mation, in which the benzo groups project away from

and the diiminato units project toward the Zr center;

i.e., the Zr binds to the backside of the macrocycle.

Despite this difference in (Me₈taa)Zr conformation, the

Zr(2)-N bond distances (average ) 2.141(9) Å) and Zr-

(2)-N₄plane displacement (1.064(5) Å) are very similar

to the corresponding values for the normal (Me₈taa)Zr

unit. Interestingly, the angle between the benzo planes

(74.3(3)°) is larger and the angle between the diiminato

planes (60.7(4)°) is smaller in the inverted macrocycle

than in the normal macrocycle, which allows proper

and ¹³C NMR data also establish that 13 has effective

C

_2vsymmetry, and the ¹⁹F NMR spectrum indicates that

-

the B(C₆F₅)₄anion is not coordinated. Additionally,

the H, ¹³C, and ¹⁹F NMR spectra of 13 are unchanged

1

down to -80 °C, which suggests that neither solvent

coordination nor anion coordination is important for this

species. Interestingly, the alkoxide methyl resonance

1

appears at high field in the H NMR spectrum (δ 0.37),

which presumably is due to anisotropic shielding from

the Me₈taa^2-benzo groups. On the basis of these

observations and data for other (Me₈taa)Zr(OR)⁺com-

plexes (vide infra ), we conclude that 13 has a mono-

nuclear, five-coordinate structure and contains a ter-

minal alkoxide ligand.

Syn th esis an d Str u ctu r es of [{Me₈taa)Zr (µ-OR)}₂]-

[B(C₆F ₅)₄]₂(R ) H, Et). One possible reason for the

lack of olefin coordination in 13 is that this species forms

a dimeric µ-alkoxide species. To probe this possibility,

we investigated the reactions of 10a with less hindered

hydroxy compounds which are more likely to result in

dimeric species. The reaction of 10a with 1 equiv of

water or ethanol in CH₂Cl₂at 23 °C yields dinuclear

(29) The Zr-olefin bonding in (C₅R₅)₂Zr(η²-O,C¹-OCMe₂CH₂CH₂-

CHdCH₂)⁺complexes is very unsymmetrical; the Zr-C¹distance is

significantly shorter than the Zr-C2 distance. See: (a) Wu, Z.; J ordan,

R. F.; Petersen, J . L. J . Am. Chem. Soc. 1995, 117, 5867. (b) Stro¨mberg,

S.; Christopher, J . C.; Lee, C. W.; Swenson, D. C.; J ordan, R. F.

Manuscript in preparation.

Synthesis of (Me₈taa)MX₂and (Me₈taa)MX⁺Complexes

Organometallics, Vol. 17, No. 3, 1998 389

Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e Refin em en t for [{Me₈ta a )Zr (µ-OH)}₂][B(C₆F ₅)₄]₂‚C₅H₁₂(14a ‚p en ta n e)

compound

color/shape

14a ‚pentane

yellow/fragment

empirical formula

C₁₀₅H₇₄B₂F₄₀N₈O₂Zr₂

fw

2443.78

temp

173(2) K

cryst syst

monoclinic

space group

P2₁/n

unit cell dimens (8192 reflections in full θ range)

a ) 16.6305(2) Å

b ) 26.3707(5) Å

c ) 24.1933(5) Å

â ) 106.799(1)°

volume

10 157.4(3) Å³

Z

4

density (calcd)

abs coeff

1.598 Mg/m³

0.334 mm^-1

diffractometer/scan

radiation/wavelength

F(000)

Siemens SMART/CCD area detector

Mo KR (graphite monochromator)/0.710 73 Å

4904

cryst size

θ range for data collection

index ranges

no. of reflns collected

no. of indep/obsd reflns

abs corr

0.10 × 0.40 × 0.40 mm

1.17-20.84°

-16 e h e 15, -26 e k e 21, -24 e l e 24

28 506

10 516 (R_int) 0.0852)/7456 ([I > 2σ(I)])

semiempirical

range of relat. transm. factors

refinement method

computing

data/restraints/params

goodness-of-fit on F²

SHELX-93 weight parameters

final R indices [I > 2σ(I)]^b

R indices (all data)

ext coeff

0.9965 and 0.8925

full-matrix-block least-squares on F²

SHELXTL, Ver. 5^a

10 508/0/1440

1.227

0.0210, 106.9067

R1 ) 0.1030, wR2 ) 0.1799

R1 ) 0.1486, wR2 ) 0.2131

0.00030(5)

largest diff. peak and hole

0.674 and -0.407 e Å^-3

a

b

_

2 _

SHELXTL, PC Version 5; Siemens Analytical X-ray Instruments, Inc.: Madison, WI. R1 ) ∑(|F_o| |F_c|)/∑F_o; wR2 ) {[∑w(F_o

F_c²)²]/[∑w(F_o²)²]}^1/2

.

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

(d eg) for [{(Me₈ta a )Zr (µ-OH)}₂][B(C₆F ₅)₄]₂(14a )

prismatic structure and minimizes interligand steric

interactions. Steric crowding between the hydroxide

groups and the C30-C42 and C35-C50 benzo groups

would be increased if the inverted (Me₈taa)Zr unit (Zr2)

adopted a normal conformation. A similar inverted

(Me₄taa)M conformation was found earlier for the main-

group compound (Me₄taa)GedTe.³⁰In contrast, singly-

bridged dinuclear compounds such as {(Me₄taa)Ti}₂(µ-

O) and {(Me₄taa)Fe}₂(µ-O),^3a,31nonbridged metal-metal

bonded compounds such as {(Me₄taa)Mo}₂and {(Me₄-

taa)Cr}₂,^32-34and the bis(ligand) sandwich compound

(Me₄taa)₂Zr^2ball exhibit normal (Me₄taa)M conforma-

tions.

The NMR data for 14a provide strong evidence that

the dimeric hydroxide-bridged structure is maintained

in solution. The ¹H NMR spectrum contains two benzo-

H, two diiminato-CH, and four methyl resonances,

consistent with the presence of two inequivalent C_2v-

symmetric (Me₈taa)Zr units. Significantly, one of the

diiminato-CH resonances (δ 5.60) appears in the normal

range observed for the (Me₈taa)Zr(X)⁺species discussed

above (δ 5.6-5.7), while the other is shifted 1.5 ppm

upfield to δ 4.14. The high-field diiminato CH reso-

nance is assigned to the methine hydrogens of the

inverted Me₈taa ligand (Zr2), which are anisotropically

Zr(1)-N(3)

Zr(1)-N(1)

Zr(1)-N(4)

Zr(2)-N(5)

Zr(2)-N(8)

Zr(2)-O(1)

2.122(10)

2.143(10)

2.198(10)

2.130(10)

2.147(10)

2.196(7)

Zr(1)-O(1)

Zr(1)-N(2)

Zr(1)-O(2)

Zr(2)-N(7)

Zr(2)-N(6)

Zr(2)-O(2)

2.141(7)

2.159(9)

2.222(7)

2.136(10)

2.152(10)

2.220(8)

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

O(1)-Zr(1)-N(1)

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

N(3)-Zr(1)-N(4)

N(1)-Zr(1)-N(4)

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

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

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

N(5)-Zr(2)-N(8)

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

N(8)-Zr(2)-N(6)

N(7)-Zr(2)-O(1)

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

N(7)-Zr(2)-O(2)

N(6)-Zr(2)-O(2)

Zr(1)-O(1)-Zr(2)

129.3(3)

98.2(3)

89.0(3)

79.2(4)

74.7(3)

94.7(3)

132.8(3)

88.5(3)

70.0(4)

81.1(4)

121.6(4)

91.2(3)

88.1(3)

138.9(3)

141.1(3)

111.5(3)

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

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

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

O(1)-Zr(1)-N(4)

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

O(1)-Zr(1)-O(2)

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

N(5)-Zr(2)-N(7)

N(7)-Zr(2)-N(8)

N(7)-Zr(2)-N(6)

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

N(8)-Zr(2)-O(1)

N(5)-Zr(2)-O(2)

N(8)-Zr(2)-O(2)

O(1)-Zr(2)-O(2)

Zr(2)-O(2)-Zr(1)

123.7(3)

75.2(3)

77.6(4)

144.8(3)

121.6(3)

70.9(3)

144.5(3)

119.2(4)

81.2(4)

70.3(4)

141.1(4)

143.5(4)

95.9(3)

92.6(3)

70.0(3)

107.6(3)

orientation of the N σ-donor orbitals for bonding with

Zr2. Thus, the bonding capability of the macrocycle

ligand is similar in both conformations. The hydroxide

bridges are symmetrical, and the Zr₂O₂unit is planar.

The two O-Zr-O angles are quite acute (Zr1, 70.9(3)°;

Zr2, 70.0(3)°) due to the constraints of the four-

membered ring structure. For comparison, the X-Zr-X

angles in (Me₄taa)ZrX₂complexes are 10-15° larger

(e.g., X ) CH₂Ph, 80.1(4)°; X ) Cl, 85.6(1)°).^2a,b,e

(30) Kuchta, M.; Parkin, G. J . Chem. Soc., Chem. Commun. 1994,

1351.

(31) Weiss, M. C.; Goedken, V. L. Inorg. Chem. 1979, 18, 819.

(32) Mandon, D.; Giraudon, J .; Toupet, L.; Sala-Pala, J .; Guerchais,

E. J . Am. Chem. Soc. 1987, 109, 3490.

(33) Edema, J . J . H.; Gambarotta, S.; van der Sluis, P.; Smeets, W.

J . J .; Spek, A. L. Inorg. Chem. 1989, 28, 3784.

(34) Cotton, F. A.; Czuchajowska, J .; Feng, X. Inorg. Chem. 1990,

29, 4329.

The unusual dinuclear structure of 14a , with one

normal and one inverted (Me₈taa)Zr unit, allows both

(Me₈taa)Zr units to achieve the favored trigonal-

390 Organometallics, Vol. 17, No. 3, 1998

Martin et al.

Sch em e 4

(Hf-C), 147.1, 141.6, and 139.1) for the butadienyl

ligand. NMR data indicate that 15 has effective C_2v

symmetry at ambient temperature, so the pendant

olefin coordinates only weakly to Hf if at all. Cationic

(C₅R₅)₂Zr(CH₃)(NMe₂Ph)⁺species (C₅R₅) C₅H₅, C₅H₄-

SiMe₃, C₅H₄CMe₃, rac-EBI) undergo similar double

insertion of internal alkynes, but in these systems a

subsequent 1,5-H shift (intramolecular C-H activation)

results in the formation of (C₅R₅)₂ZrCH₂CRdCR-

CRdCRH)⁺pentadienyl species.³⁵

Cation 10d inserts 1-(trimethylsilyl)-1-propyne (<1

h, 23 °C) more rapidly to yield [(Me₈taa)Hf-

(C(SiMe₃)dCMe₂)][B(C₆F₅)₄] (16), which was isolated

(80%) as an orange solid (Scheme 4). The alkenyl

regiochemistry is assigned on the basis of hydrolysis

experiments, which gave 2-methyl-1-(trimethylsilyl)-

1

shielded due to their proximity to the benzo groups of

the normal Me₈taa ligand in the dinuclear structure.

The ¹³C NMR spectrum of 14a also contains two sets of

Me₈taa resonances, including one normal methine reso-

nance (δ 107.3; cf. δ 106-108 for other (Me₈taa)Zr(X)⁺

species) and one high-field methine resonance (δ 90.2).

The NMR data for the ethoxide complex 14b are similar

to those for 14a ; in particular high-field methine

resonances for the inverted Me₈taa ligand are observed

propene. The H NMR spectrum of 16 at -20 °C con-

tains two benzo-H, two diiminato-CH, and four methyl

resonances for the Me₈taa ligand, which establishes that

this species adopts a C_s-symmetric structure. However,

at 23 °C, the two benzo-H resonances are collapsed to

one resonance and the remaining Me₈taa resonances are

broadened, consistent with the existence of a dynamic

process which renders the sides of the Me₈taa ligand

equivalent. Similarly, the low-temperature (-20 °C) ¹³

C

1

in the H and ¹³C NMR spectra. The spectra for 14b

NMR spectrum of 16 is consistent with a C_s-symmetric

structure, but the Me₈taa resonances are broadened at

room temperature. These observations suggest that a

weak Hf- - -Me₃Si agostic interaction which hinders

rotation around the Hf-C bond is present in 16;

however, this issue was not probed further. Complex

16 does not insert a second equivalent of (Me₃Si)CtCMe.

Similar 2,1-insertions of silylalkynes are observed for

Cp₂MR⁺species (M ) Ti, Zr).^36,37Agostic coordination

of a Si-Me group was observed in [Cp₂Zr(C(SiMe₃)d

CMe₂)][B(C₆F₅)₄],^36aand the acute Ti-C-Si angle (88.9°)

in [Cp₂Ti(C(SiMe₃)dCMePh)][AlCl₄] suggests that a

similar interaction may be present in this species as

well.³⁷

also contain a single set of ethyl resonances, which is

consistent with the equivalence of the two ethoxide

ligands in the proposed dinuclear structure.

The NMR spectra of 13 contain resonances for a single

C_2v-symmetric (Me₈taa)Zr unit and lack the high-field

methine resonances which are characteristic of the

dinuclear structures of 14a ,b, thus implying that 13

does not have a similar dinuclear structure. Presum-

ably, the steric bulk of the alkoxide ligand in 13

disfavors alkoxide bridging. Inspection of the structure

of 14a suggests that steric crowding would disfavor a

dinuclear structure with two normal (Me₈taa)Zr units

for 13.

Com par ative Olefin Bin din g Affin ity of (Me₈taa)-

MR⁺a n d (C₅R₅)₂MR⁺. The results described in the

last two sections show that (Me₈taa)Zr(OR)⁺species

have a lower affinity for olefin binding than do (C₅R₅)₂-

Zr(OR)⁺species, at least in the intramolecular case

studied, and suggest that the corresponding cationic

alkyl species, (Me₈taa)MR⁺and (C₅R₅)₂MR⁺, would

show a similar difference in olefin binding affinity.

However, it should be noted that extrapolation from

alkoxide compounds to alkyl compounds may be com-

plicated by the differences in the frontier-orbital proper-

ties of the (Me₈taa)M²⁺and Cp₂M²⁺fragments noted

in the introduction. Oxygen-M π-donation to both the

d_xzand the d_yzorbitals is possible in a five-coordinate

(Me₈taa)M(OR)⁺cation, while only a single O-M π bond

can form in a Cp₂M(OR)⁺cation. The selective enhance-

ment of O-M π-donation in (Me₈taa)M(OR)⁺may

disfavor olefin coordination. Studies of this issue are

continuing.

In contrast, neither 10a nor 10b react with these

alkynes under similar conditions. Steric factors are

expected to strongly influence the reactivity of (Me₈taa)-

MR⁺species with alkynes. Additionally, the Zr-Ph

interaction in 10a may inhibit alkyne coordination as

well as migratory insertion,³⁸and electronic interactions

may stabilize 10b toward migratory insertion (σ hyper-

conjugation; Si R to nucleophilic Zr-C and â to Zr).³⁹

The base-stabilized (Me₈taa)Zr(R)(L)⁺species 11 are

also unreactive with these alkynes.

Rea ction s of (Me₈ta a )M(R)⁺Sp ecies w ith Ter -

m in a l Alk yn es. Complexes 10a and 10c react with

phenylacetylene and 1-pentyne (CH₂Cl₂, 23 °C, <30

min, excess alkyne) to yield the dinuclear µ-alkynyl

complexes 17 and toluene or neopentane, respectively

(35) Horton, A. D.; Orpen, A. G. Organometallics 1992, 11, 8.

(36) (a) Horton, A. D.; Orpen, A. G. Organometallics 1992, 11, 8.

(b) Guram, A. S.; J ordan, R. F. Organometallics 1991, 10, 3470.

(37) Eisch, J . J .; Piotrowski, A. M.; Brownstein, S. K.; Gabe, E. J .;

Lee, F. L. J . Am. Chem. Soc. 1985, 107, 7219.

Rea ction s of (Me₈ta a )M(R)⁺Com p lexes w ith

In ter n a l Alk yn es. Cationic Hf methyl complex 10d

reacts with excess 2-butyne (CH₂Cl₂, 23 °C, 12 h) to yield

the double-insertion product [(Me₈taa)Hf(CMedCMe-

CMedCMe₂)][B(C₆F₅)₄] (15, Scheme 4), which is isolated

as a golden brown solid (78%). The ¹³C NMR spectrum

of 15 contains four alkenyl carbon resonances (δ 214.0

(38) The lower reactivity of CH₃CN with Cp₂Zr(η²-CH₂Ph)(CH₃CN)⁺

versus Cp₂ZrCH₃(CH₃CN)⁺was ascribed to stabilization by the Zr- -

-Ph interaction, see: Wang, Y.; J ordan, R. F.; Echols, S. F.; Borkowsky,

S. L.; Bradley, P. K. Organometallics 1991, 10, 1406.

(39) (a) Eisch, J . J .; Caldwell, K. R.; Werner, S.; Kru¨ger, C.

Organometallics 1991, 10, 3417. (b) Koga, N.; Morokuma, K. J . Am.

Chem. Soc. 1988, 110, 108. (c) Guram, A. S.; J ordan, R. F. Organo-

metallics 1990, 9, 2190.

Synthesis of (Me₈taa)MX₂and (Me₈taa)MX⁺Complexes

Organometallics, Vol. 17, No. 3, 1998 391

which the metals have d⁰electron configurations nor-

mally exhibit µ-η¹:η¹alkynyl bridges, as in {Cp₂Er(µ-

CtC^tBu)}₂and {Cp₂Zr}₂(µ-CtCMe)(µ-MeCdCMe)⁺.^41,42

This alkynyl bonding mode is characterized by IR ν_CC

values (2000-2050 cm^-1) and ¹³C NMR chemical shifts

(δ 100-130) which are similar to those for terminal

alkynyl compounds and reflect the retention of the CtC

triple bond. In contrast, dⁿ,dⁿsystems (n g 1) typically

adopt µ-η¹:η²structures, as in {(C₅H₄Me)₂Zr(µ-CCPh)}₂

and Cp₂Zr(µ-CCSiMe₃)₂Ni(PPh₃).⁴³In these cases, re-

duced ν_CCvalues (1750-1900 cm^-1), reflecting the

reduced CC bond order, and low-field ¹³C chemical shifts

for the M-CCR carbon (δ > 200) are observed. The

spectroscopic data for 17a ,b are consistent with the

expected µ-η¹:η¹-bonding mode. The ¹³C NMR reso-

nances for the alkynyl carbons appear at δ 121.0 and

119.0 for 17a and at δ 125.5 and 115.0 for 17b. The IR

Sch em e 5

spectrum of 17a displays a ν_CCband at 2034 cm^-1

.

Complexes 17a ,b do not react further with excess

alkyne and do not catalyze alkyne oligomerization under

mild conditions. Heating a CD₂ClCD₂Cl solution of 17a

(65 °C, 24 h) with excess phenylacetylene resulted in a

complex mixture of products with no apparent reaction

of the phenylacetylene, and 17b does not react with

excess 1-pentyne at 65 °C (24 h). This lack of reactivity

contrasts with the catalytic oligomerization of terminal

alkynes observed for Cp*₂ZrR⁺and many other d⁰metal

alkynyl complexes, which proceeds by sequential inser-

tion/σ-bond metathesis steps.^44-47

Ch a r t 2

One likely reason for the lack of reactivity of 17a ,b

with alkynes is that the dinuclear structures are too

robust to allow alkyne coordination. To probe this issue,

the reaction of 17a with the stronger Lewis base PMe₃

was investigated by NMR spectroscopy. Complex 17a

reacts cleanly with excess PMe₃(3 equiv, 23 °C, CH₂-

Cl₂, 1 h) to afford the PMe₃adduct (Me₈taa)Zr(CtCPh)-

(PMe₃)⁺(18a , >90% NMR, Scheme 5). The low-

(Scheme 5). Complexes 17a and 17b were isolated as

yellow solids in 76% and 92% yield, respectively. These

reactions proceed by protonolysis of the Zr-C bond by

the acidic alkyne hydrogen and subsequent dimerization

to stabilize the unsaturated metal center.

The ¹H and ¹³C NMR spectra of 17a ,b (23 °C) are

similar to those observed for µ-OR complexes 14 and

establish that these cations adopt similar dinuclear

(41) For representative examples, see: (a) Forsyth, C. M.; Nolan,

S. P.; Stern, C. L.; Marks, T. J . Organometallics 1993, 12, 3618. (b)

Shen, Q.; Zheng, D.; Lin, L.; Lin, Y. J . Organomet. Chem. 1990, 391,

307. (c) Boncella, J . M.; Tilley, T. D.; Andersen, R. A. J . Chem. Soc.,

Chem. Commun. 1984, 710. (d) Evans, W.; Bloom, I.; Hunter, W. E.;

Atwood, J . L. Organometallics 1983, 2, 709. (e) Atwood, J . L.; Hunter,

W. E.; Wayda, A. L.; Evans, W. J . Inorg. Chem. 1981, 20, 4115. (f)

Lee, L.; Berg, D. J .; Bushnell, G. W. Organometallics 1995, 14, 5021.

(g) Almenningen, A.; Fernholt, L.; Haaland, A. J . Organomet. Chem.

1978, 155, 245. (h) Morosin, B.; Howatson, J . J . Organomet. Chem.

1971, 29, 7.

(42) For cationic Cp₂Zr examples, see: (a) Ro¨ttger, D.; Erker, G.;

Fro¨hlich, R.; Grehl, M.; Silverio, S. J .; Hyla-Kryspin, I.; Gleiter, R. J .

Am. Chem. Soc. 1995, 117, 10503. (b) Horton, A. D.; Orpen, A. G.

Angew. Chem., Int. Ed. Engl. 1992, 31, 876.

(43) For representative examples, see: (a) Erker, G.; Fro¨mberg, W.;

Benn, R.; Mynott, R.; Angermund, K.; Kru¨ger, C. Organometallics

1989, 8, 911. (b) Rosenthal, U.; Pulst, S.; Arndt, P.; Ohff, A.; Tillac,

A.; Baumann, W.; Kempe, R.; Burkalov, V. V. Organometallics 1995,

14, 2961. (c) Erker, G.; Fro¨mberg, W.; Mynott, R.; Gabor, B.; Kru¨ger,

C. Angew. Chem., Int. Ed. Engl. 1986, 25, 463. (d) Cowie, M.; Loeb, S.

J . Organometallics 1985, 4, 852.

(44) Horton, A. D. J . Chem. Soc., Chem. Commun. 1992, 185.

(45) For leading references, see: (a) den Haan, K. H.; Wielstra, Y.;

Teuben, J . H. Organometallics 1987, 6, 2053. (b) Heeres, H. J .; Teuben,

J . H. Organometallics 1991, 10, 1980. (c) Straub, T.; Haskel, A.; Eisen,

M. S. J . Am. Chem. Soc. 1995, 117, 6364. (d) St. Clair, M.; Schaefer,

W. P.; Bercaw, J . E. Organometallics 1991, 10, 525. (e) Heeres, H. J .;

Nijhoff, J .; Teuben, J . H.; Rogers, R. D. Organometallics 1993, 12, 2609.

For alkyne oligomerization by late metal complexes, see: (f) Trost, B.

M.; Sorum, M. T.; Chan, C.; Harms, A. E.; Ruchter, G. J . Am. Chem.

Soc. 1997, 119, 698. (g) Bianchini, C.; Frediani, P.; Masi, D.; Peruzzini,

M.; Zanobini, F. Organometallics 1994, 13, 4616.

1

structures. The H NMR spectrum of 17a contains one

set of phenyl resonances for the two equivalent -CCPh

ligands and two benzo-H, two diiminato-CH, and four

methyl resonances for the two inequivalent C_2v-sym-

metric (Me₈taa)Zr units. One Me₈taa-methine reso-

nance (δ 4.09) is shifted upfield from the normal range

observed for mononuclear (Me₈taa)Zr(X)⁺species (δ

5.6-5.7) and is assigned to the methine hydrogen of the

inverted (Me₈taa)Zr unit of the dinuclear cation. The

other methine signal (δ 5.25) appears close to the

normal range and is assigned to the methine hydrogen

of the normal (Me₈taa)Zr unit. The ca. 0.4 ppm upfield

shifting of this resonance is due to anisotropic shielding

1

by the alkynyl group. The H NMR data for 17b are

similar to those for 17a , and the ¹³C NMR spectra of

both cations contain one normal and one high-field

methine resonance.

Bridging alkynyl complexes, L_nM(µ-CCR)ML_n, exhibit

a variety of bonding modes (Chart 2), ranging from µ-η¹:

η¹(or µ-σ:σ; A) structures to highly unsymmetric µ-η¹:

η²(or µ-σ:π; B) structures in which the alkynyl ligand

is σ-bonded to one metal and forms a π-complex with

the second.⁴⁰Binuclear L_nM(µ-CCR)ML_ncomplexes in

(46) For Ti catalyst, see: (a) Akita, M.; Yasuda, H.; Nakamura, A.

Bull. Chem. Soc. J pn. 1984, 57, 480. (b) Varga, V.; Petrusova´, L.; Cejka,

J .; Hanus, V.; Mach, K. J . Organomet. Chem. 1996, 509, 235.

(47) Yoshida, M.; J ordan, R. F. Organometallics 1997, 16, 4508.

(40) Kumar, P. N. V. P.; J emmis, E. D. J . Am. Chem. Soc. 1988,

110, 125 and references therein.

392 Organometallics, Vol. 17, No. 3, 1998

Martin et al.

temperature (<-80 °C) ¹H NMR spectrum of 18a shows

that this species has a C_s-symmetric structure and

contains one coordinated PMe₃ligand. Complex 18a

undergoes rapid (NMR time scale) exchange with free

PMe₃above ca. -80 °C. Attempts to isolate complex

18a by crystallization from CH₂Cl₂/hydrocarbon solvents

followed by drying under vacuum yielded 17a . Thus,

17a only reversibly coordinates PMe₃. Therefore, it is

reasonable that cleavage of the dinuclear structure of

17a by coordination of alkynes, which are expected to

be much weaker Lewis bases for the d⁰cation, is

disfavored.

may reflect both the lower Lewis acidity and the harder

character of these metal cations as compared to Cp₂-

MR⁺. More highly unsaturated three- and four-coordi-

nate cationic group 4 metal alkyls containing nitrogen-

and oxygen-based ligands, such as {(2,6-ⁱPr₂-C₆H₃)-

N(CH₂)₃N(2,6-ⁱPr₂-C₆H₃)}TiR⁺and [{(^tBu-d₆)N-o-C₆H₄}₂-

O]ZrR⁺, are more reactive with olefins than are (Me₈-

taa)MR⁺species.⁴⁸Benzamidinate-stabilized yttrium

alkyls {PhC(NSiMe₃)₂}₂YR are less reactive for alkene

and alkyne insertion than are (C₅R₅)₂YR metallocenes,

which was ascribed to the higher ionic character of the

former systems which disfavors π-complex formation

with unsaturated hydrocarbons.⁴⁹

Con clu sion s

The formation of dinuclear mono- and dications, e.g.,

(Me₈taa)Zr(µ-NMe₂)₂AlMe₂⁺, {(Me₈taa)Zr(µ-OR)}₂²⁺, and

{(Me₈taa)Zr(µ-CCR)}₂²⁺, is a general feature of group 4

Me₈taa^2-chemistry. The sterically open out-of-plane

structures, the conformational flexibility of the (Me₈-

taa)Zr fragment, the delocalization of the positive charge

onto the Me₈taa^2-ligands, and the nucleophilic char-

acter of the X^-ligands in (Me₈taa)MX₂and (Me₈taa)-

MX⁺species favor the formation of bridged dinuclear

complexes.

Salt-elimination, alkane-elimination, and amine-

elimination reactions provide access to a wide variety

of (Me₈taa)MX₂chloride, alkyl, and amide complexes.

NMR data for these complexes and the cationic species

derived from them are in accord with cis, out-of-plane

structures similar to those established previously for the

(Me₄taa)MX₂analogues.^1-4(Me₈taa)ZrMe₂undergoes

metal-to-ligand methyl migration in the presence of

Lewis bases, but the bulkier Zr analogues and the Hf

alkyls are resistant to this process.

(Me₈taa)MR₂alkyls react under mild conditions with

CHCl₂CHCl₂and CH₂Cl₂to yield RH and (Me₈taa)MCl₂.

(Me₈taa)Zr(NMe₂)₂reacts with CH₂Cl₂via nucleophilic

chloride displacement to yield CH₂(NMe₂)₂and (Me₈-

taa)ZrCl₂and with AlMe₃by nucleophilic substitution

to yield [(Me₈taa)Zr(µ-NMe₂)₂AlMe₂][AlMe₄]. These

reactions indicate that the alkyl and amide ligands in

these systems are very nucleophilic and imply that the

M-R and M-NR₂bonds are highly polarized. This

property appears to be enhanced relative to Cp₂MR₂

systems, which may reflect the harder character of the

Exp er im en ta l Section

Gen er a l P r oced u r es. All manipulations were performed

on a high-vacuum line or in a glovebox under a purified N₂

atmosphere. Solvents were distilled from Na/benzophenone,

except for the chlorinated solvents which were distilled from

activated molecular sieves (3 Å) or P₂O₅. (Me₈taa)H₂,¹⁰Zr(CH₂-

CMe₃)₄,⁵⁰Zr(CH₂Ph)₄,⁵¹MCl₄(THF)₂(M ) Zr, Hf),⁵²and Zr-

(NR₂)₄(R ) Me, Et)^21,22were prepared by literature procedures.

Solid MeLi was obtained by evaporating a commercial Et₂O

solution of MeLi under vacuum and drying the resulting white

solid under high vacuum for 0.5 h at 110 °C. Li[B(C₆F₅)₄] was

prepared from BCl₃and 4 equiv of Li[C₆F₅] (generated in situ)

in Et₂O at -78 °C.⁵³[HNMe₂Ph][B(C₆F₅)₄] and [HNMePh₂]-

[B(C₆F₅)₄] were prepared by metathesis of Li[B(C₆F₅)₄] with

[NMe₂PhH]Cl and [NMePh₂H]Cl, respectively, in degassed

H₂O.

Me₈taa^2-versus the Cp₂ancillary ligands.

2-

Cationic (Me₈taa)MR⁺species are formed by proto-

nolysis of (Me₈taa)MR₂complexes by noncoordinating

ammonium reagents and are thermally stable as the

-

B(C₆F₅)₄salts. NMR data are in accord with five-

NMR spectra were recorded on a Bruker AMX 360 or AC

300 (¹⁹F) spectrometer in sealed or Teflon-valved tubes at

ambient-probe temperature unless otherwise indicated. ¹H

and ¹³C NMR chemical shifts are reported versus SiMe₄and

were determined by reference to the residual ¹H and ¹³C

solvent peaks. Coupling constants are reported in hertz. The

spectra of the cationic complexes contained resonances for free

coordinate square-pyramidal structures. While (Me₈-

taa)Zr(η²-CH₂Ph)⁺exhibits a weak Zr- - -Ph interaction,

agostic M- - -H-C interactions are weak at best in (Me₈-

taa)M(CH₂R)⁺alkyls, and no evidence for strong solvent

coordination or site-specific ion-pairing is observed for

these species in CH₂Cl₂solution. While (Me₈taa)Zr(η²-

CH₂Ph)⁺polymerizes ethylene and (Me₈taa)HfMe⁺in-

serts internal alkynes, in general (Me₈taa)MR⁺species

are significantly less reactive toward alkene and alkyne

insertion than are Cp₂MR⁺cations.^7,44As (Me₈taa)MR⁺

cations are not sterically crowded and the M-R bonds

are highly polarized, the lack of insertion reactivity

probably reflects a low tendency for these cations to form

π complexes with (and hence activate) alkenes and

alkynes. The observation that (Me₈taa)Zr(OCMe₂CH₂-

CH₂CHdCH₂)⁺does not coordinate the pendant alkene

while (C₅R₅)₂Zr(η²-O,C¹-OCMe₂CH₂CH₂CHdCH₂)⁺spe-

cies adopt chelated structures supports the supposition

that (Me₈taa)MR⁺cations have a lower affinity for

unsaturated hydrocarbons than do Cp₂MR⁺cations.

However, as noted above, differences in the frontier-

orbital properties of the (Me₈taa)M²⁺and Cp₂M²⁺frag-

ments may complicate this comparison. The reluctance

of (Me₈taa)MR⁺to coordinate unsaturated hydrocarbons

-

B(C₆F₅)₄or BPh₄anions.^54,55The spectra of the cationic

complexes generated in situ also contained resonances for free

(48) (a) Scollard, J . D.; McConville, D. H. J . Am. Chem. Soc. 1996,

118, 10008. (b) Scollard, J . D.; McConville, D. H.; Payne, N. C.; Vittal,

J . J . Macromolecules 1996, 29, 5241. (c) Baumann, R.; Davis, W. M.;

Schrock, R. R. J . Am. Chem. Soc. 1997, 119, 3830. (d) Horton, A. D.;

de With, J .; van der Linden, A. J .; van de Weg, H. Organometallics

1996, 15, 2672. (e) van der Linden, A. J .; Schaverien, C. J .; Meijboom,

N.; Ganter, C.; Orpen, A. G. J . Am. Chem. Soc. 1995, 117, 3008.

(49) Duchateau, R.; van Wee, C. T.; Teuben, J . H. Organometallics

1996, 15, 2291.

(50) Collier, M. R.; Lappert, M. F. J . Chem Soc., Dalton Trans. 1973,

445.

(51) Zucchini, U.; Aldizzati, E.; Giannini, U. J . Organomet. Chem.

1971, 26, 357.

(52) Manzer, L. E. Inorg. Synth. 1982, 21, 135.

(53) Massey, A. G.; Park, A. J . J . Organomet. Chem. 1964, 2, 245.

-

1

(54) B(C₆F₅)₄

:

¹³C NMR (C₂D₂Cl₄) δ 146.6 (dm, J _CF) 245), 136.6

1

(dm, J _CF) 245), 134.6 (dm, J _CF) 244), 122.6 (br m, BC).

:

¹H NMR (CD₂Cl₂) δ 7.37 (m, 8 H), 7.04 (t, J ) 7, 8 H),

-

(55) BPh₄

6.89 (t, J ) 7, 4 H); {¹H}¹³C NMR (CD₂Cl₂) δ 164.3 (q, J _BC) 49, ipso),

136.2, 126.0, 122.2.

Synthesis of (Me₈taa)MX₂and (Me₈taa)MX⁺Complexes

Organometallics, Vol. 17, No. 3, 1998 393

NMe₂Ph or NBu₃.^56,57Elemental analyses were performed by

E & R Microanalytical Laboratory, Inc.

CH₂Cl₂/hexane to give a second crop of yellow solid, which was

dried as above (1.25 g total, 71%). ¹H NMR (CD₂Cl₂): δ 7.24

(s, 4 H), 5.57 (s, 2 H, NCdCHsCN), 2.47 (s, 12 H), 2.39 (s, 12

H). Gated-{¹H}-¹³C NMR (CD₂Cl₂): δ 159.6 (m, CdN), 138.4

(benzo-CN), 127.0 (d, J ) 6, benzo-CMe), 126.5 (dm, J ) 160,

benzo-CH), 105.3 (dm, J ) 160, NCdCHsCN), 23.3 (qd, J )

128, 4), 20.4 (qd, J ) 127, 5). Anal. Calcd for C₂₆H₃₀Cl₂HfN₄:

C, 48.20; H, 4.67; N, 8.65; Cl, 10.94. Found: C, 48.08; H, 4.61;

N, 8.49; Cl, 10.70.

In some cases, the neutral dialkyl and dichloro complexes

were initially isolated containing traces of very fine, insoluble

material (e.g., LiCl in 2a ,b, 3a ,b, and 4a ,b) which could not

be removed by filtration or which would clog fritted glass

filters. These impurities could best be removed by centrifuga-

tion. Once this was done, further purification was usually

unnecessary; however, most of the neutral complexes could

be recrystallized if desired.

(Me₈ta a )Zr (CH₂SiMe₃)₂(3a ). A pentane solution of LiCH₂-

SiMe₃(1.0 M, 6.6 mL, 6.6 mmol) was added to a rapidly stirred

slurry of 2a (1.5 g, 2.7 mmol) in toluene (100 mL). Additional

toluene (25 mL) was added to facilitate stirring. The mixture

was stirred for 1 h and filtered. The filter cake was washed

with toluene (5 × 15 mL), and the combined filtrates were

evaporated under vacuum. The residue was slurried in

toluene (25 mL) and centrifuged. The homogeneous orange

supernatant was decanted off, and this process was repeated

4 times. The supernatants were combined and concentrated

under vacuum to 20 mL, giving a slurry. Pentane (20 mL)

was added, and the slurry was filtered to give an orange solid,

which was washed with pentane (2 × 5 mL) and dried under

high vacuum overnight. The mother liquor was evaporated

under vacuum, and the residue was recrystallized from

toluene/pentane to give a second crop of orange solid, which

was dried as above (1.29 g total, 72%). ¹H NMR analysis

indicated the presence of ca. 0.5 equiv of toluene. ¹H NMR

(C₆D₆): δ 7.22 (s, 4 H), 5.04 (s, 2 H, NCdCHsCN), 2.07 (s, 24

H, the two sets of 4 Me’s are coincident), 0.08 (s, 18 H), 0.06

(s, 4 H, ZrCH₂). Gated-{¹H}-¹³C NMR (C₆D₆): δ 158.6 (m,

NdC), 135.2 (m, benzo-CN), 131.6 (d, J ) 7, benzo-CMe), 126.4

(dm, J ) 158, benzo-CH), 103.6 (dm, J ) 157, NCdCHsCN),

43.8 (t, J ) 104, ZrCH₂), 23.1 (qd, J ) 128, 4, Me), 20.0 (qd, J

) 126, 5, Me), 3.9 (q, J ) 117, SiMe₃). A solvent-free sample

of 3a was prepared by dissolving the above toluene solvate of

3a (220 mg) in CH₂Cl₂(5 mL), evaporating the solvent under

vacuum, and drying the residue under high vacuum for 1 day.

This sample was spectroscopically pure, but duplicate analysis

gave low C values, possibly due to SiC formation during

analysis. Anal. Calcd for C₃₄H₅₂N₄Si₂Zr: C, 61.48; H, 7.89;

N, 8.44. Found: C, 59.81 and 59.68; H, 7.56; N, 8.52.

(Me₈ta a )Zr Me₂(3b). A slurry of 2a (1.1 g, 2.0 mmol) and

solid MeLi (86 mg, 3.9 mmol) in toluene (40 mL) was stirred

at -78 °C for 1 day and at 0 °C for 2 days and filtered. The

solvent was evaporated under vacuum, and the orange solid

residue was dried under high vacuum for 3 h (150 mg, 15%).

¹H NMR (C₆D₆): δ 7.12 (s, 4 H), 5.10 (s, 2 H, NCdCHsCN),

2.11 (s, 12 H), 1.98 (s, 12 H), 0.14 (s, 6 H, ZrCH₃). Gated-

{¹H}-¹³C NMR (C₆D₆): δ 158.4 (CdN), 135.2 (benzo-CN),

131.3 (benzo-CMe), 126.0 (dd, J ) 153, 5, benzo-CH), 103.2

(d, J ) 157, NCdCHsCN), 30.4 (q, J ) 111, ZrCH₃), 22.9 (qd,

J ) 118, 4), 19.9 (qd, J ) 122, 5). Anal. Calcd for C₂₈H₃₆N₄-

Zr: C, 64.69; H, 6.98; N, 10.78; Zr, 17.55. Found: C, 64.36;

H, 6.85; N, 10.50; Zr, 17.98. Attempts to scale up this reaction,

recrystallize the product, or isolate additional product were

unsuccessful.

[Li(Et₂O)]₂[Me₈ta a ] (1). A solution of MeLi in Et₂O (1.4

M, 18 mL, 25 mmol) was added over 15 min to a rapidly stirred

slurry of (Me₈taa)H₂(5.0 g, 12 mmol) in Et₂O (200 mL). The

evolution of CH₄diminished with addition of the last aliquot.

The deep purple mixture was stirred for 3 h and concentrated

under vacuum to 40 mL. Pentane (10 mL) was added, and

the mixture was filtered to give a purple solid, which was

broken up with a spatula and dried under high vacuum for 3

h (6.2 g, 92%). ¹H NMR (THF-d₈): δ 6.54 (s, 4 H), 4.42 (s, 2

H, NCdCH-CN), 3.39 (q, J ) 7, 8 H, Et₂O), 2.11 (s, 12 H),

2.08 (s, 12 H), 1.12 (t, J ) 7, 12 H, Et₂O). {¹H}¹³C NMR (THF-

d₈): δ 160.3 (NdC), 145.0 (benzo-CN), 127.7 (benzo-CMe),

123.1 (benzo-CH), 98.8 (NCdCHsCN), 66.3 (Et₂O), 22.8, 19.7,

15.7 (Et₂O). Anal. Calcd for C₃₄H₅₀Li₂N₄O₂: C, 72.83; H, 8.99;

N, 9.99. Found: C, 72.81; H, 8.78; N, 10.24.

(Me₈ta a )Zr Cl₂(2a ). A slurry of 1 (2.8 g, 5.0 mmol) and

ZrCl₄(THF)₂(1.9 g, 5.0 mmol) in THF (40 mL) was stirred for

19 h, concentrated under vacuum to 25 mL, and filtered. The

yellow solid was washed with THF (3 × 5 mL) and dried under

high vacuum for 10 min at 70 °C to remove residual solvent.

Methylene chloride (25 mL) was added, and the mixture was

centrifuged. The resulting homogeneous yellow supernatant

was decanted and cooled to -35 °C overnight. Yellow crystals

were isolated by filtration and dried under high vacuum for 6

h at 80 °C. The mother liquor was concentrated under vacuum

to 10 mL. Pentane was layered onto the slurry, and the

mixture was placed in a -35 °C freezer overnight. A second

crop of a yellow solid was isolated by filtration and dried as

described above (2.20 g total, 78%). ¹H NMR (CD₂Cl₂): δ 7.40

(s, 4 H), 5.65 (s, 2 H, NCdCHsCN), 2.49 (s, 12 H), 2.42 (s, 12

H). {¹H}¹³C NMR (CD₂Cl₂): δ 158.4 (NdC), 139.2 (benzo-CN),

127.0 (benzo-CMe), 126.2 (benzo-CH), 105.3 (NCdCHsCN),

23.0, 20.4. In a similar experiment, the yellow solid isolated

from the original THF slurry was dried under high vacuum

1

at 23 °C to give a THF solvate of 2a (0.75 equiv by H NMR),

which was submitted for analysis. Anal. Calcd for C₂₉H₃₆

-

Cl₂N₄O_0.75Zr: C, 56.66; H, 5.90; N, 9.11; Cl, 11.53. Found: C,

56.82; H, 5.91; N, 8.85; Cl, 10.66.

(Me₈ta a )HfCl₂(2b). A slurry of 1 (1.52 g, 2.71 mmol) and

HfCl₄(THF)₂(1.26 g, 2.71 mmol) in THF (50 mL) was stirred

for 2 h at 23 °C, refluxed for 15 min, concentrated under

vacuum to 10 mL, and filtered to yield a yellow solid. This

solid was washed with THF (2 × 2 mL) and dried under high

vacuum overnight at 90 °C. The solid was taken up in CH₂-

Cl₂(15 mL), and the slurry was centrifuged. The supernatant

was evaporated under vacuum, and the resulting yellow solid

was washed with hexane and dried under high vacuum

overnight at 70 °C. The original THF mother liquor and the

THF washes were combined and evaporated under vacuum.

The residue was slurried in benzene (25 mL) and centrifuged.

The supernatant was decanted off, and this process was

repeated 7 times. The combined supernatants were evapo-

rated under vacuum, and the residue was recrystallized from

(Me₈ta a )Zr (CH₂P h )₂(3c). A slurry of (Me₈taa)H₂(1.8 g,

4.4 mmol) and Zr(CH₂Ph)₄(2.0 g, 4.4 mmol) in pentane (75

mL) was stirred for 14 h at 23 °C. An orange solid was isolated

by filtration, washed with pentane (2 × 10 mL), and dried

under high vacuum for 1 h (2.8 g, 95%). This complex is only

sparingly soluble in C₆H₆. ¹H NMR (CD₂Cl₂): δ 7.12 (s, 4 H),

6.91 (t, J ) 8, 4 H, meta-benzyl), 6.57 (t, J ) 7, 2 H, para-

benzyl), 6.39 (d, J ) 8, 4 H, ortho-benzyl), 5.08 (s, 2 H,

NCdCHsCN), 2.39 (s, 12 H), 2.23 (s, 12 H), 1.20 (s, 4 H,

ZrCH₂). {¹H}¹³C NMR (CD₂Cl₂): δ 158.6 (CdN), 153.9 (ipso-

Ph), 136.6 (benzo-CN), 128.8, 127.1, 126.4, 124.6, 117.7, 103.6

(NCdCHsCN), 59.6 (ZrCH₂, J _CH) 119 from gated-{¹H}

spectrum), 23.1, 20.3. Anal. Calcd for C₄₀H₄₄N₄Zr: C, 71.49;

H, 6.60; N, 8.34; Zr, 13.57. Found: C, 71.73; H, 6.71; N, 8.21;

Zr, 13.62.

(56) NMe₂Ph: ¹H NMR (C₂D₂Cl₄) 7.22 (t, 2 H, Ph), 6.70 (m, 3 H,

Ph), 2.91 (s, 6 H, Me). In certain cases, minor shifts (<0.05 ppm) are

observed due to trace excesses of [HNMe₂Ph][B(C₆F₅)₄], differences in

ionic strength, or other factors. Gated-{¹H}-¹³C NMR (C₂D₂Cl₄): 149.0

(m, ipso), 127.6 (dd, J ) 158, 8, m), 115.2 (d, J ) 160, p), 111.2 (d, J

) 156, o), 39.1 (q, J ) 137, NMe₂Ph).

(57) NBu₃: ¹H NMR (CD₂Cl₂) δ 2.32 (m, 6 H), 1.30 (m, 12 H), 0.91

(t, J ) 7, 9 H).

394 Organometallics, Vol. 17, No. 3, 1998

Martin et al.

The ¹H NMR spectrum of 3c in THF-d₈exhibits a compli-

cated pattern of resonances, most likely as a result of THF-

induced migration of a benzyl group to a Me₈taa imine carbon.

(Me₈ta a )Zr (CH₂CMe₃)₂(3d ). A slurry of (Me₈taa)H₂(1.14

g, 2.84 mmol), and Zr(CH₂CMe₃)₄(1.07g, 2.84 mmol) was

stirred in toluene (40 mL) at 50 °C for 5 days. The red solution

was cooled to 23 °C, which resulted in crystallization of a red

solid, which was collected by filtration, washed with pentane

(2 × 10 mL), and dried under high vacuum overnight. The

mother liquor was concentrated to dryness, slurried in hexane,

and filtered to obtain a second crop of orange solid. This solid

was recrystallized from a mixture of toluene (10 mL) and

pentane (5 mL) at -40 °C overnight, isolated by filtration,

washed with pentane (2 × 5 mL), and dried under high

vacuum overnight. Total yield: 0.774 g (43.1%). ¹H NMR

(C₆D₆) δ: 7.25 (s, 4 H), 5.04 (s, 2 H, NCdCHsCN), 2.07 (s, 12

H), 2.00 (s, 12 H), 1.19 (s, 18 H, CH₂CMe₃), 0.84 (s, 4 H, CH₂-

CMe₃). Gated-{¹H}-¹³C NMR (C₆D₆) δ: 158.6 (M, CdN), 135.4

(m, benzo-CN), 133.1 (d, J ) 4, benzo-CMe), 125.4 (dm, J )

151, benzo-CH), 103.0 (dm, J ) 157, NCdCHsCN), 77.2 (tm,

J ) 108, ZrCH₂), 35.5 (m, CH₂CMe₃and qm, J ) 122, C(CH₃)₃),

22.8 (qd, J ) 127, 4, Me), 19.8 (qd, J ) 125, 5, Me). Anal.

Calcd for C₃₆H₅₂N₄Zr: C, 68.41; H, 8.29; N, 8.86. Found: C,

68.28; H, 8.11; N, 8.64.

(Me₈ta a )Hf(CH₂SiMe₃)₂(4a ). A slurry of 2b (320 mg, 0.49

mmol) and solid LiCH₂SiMe₃(obtained from evaporation of a

pentane solution of LiCH₂SiMe₃, 92 mg, 0.98 mmol) in C₆H₆

(50 mL) was stirred for 1 h. The mixture was filtered, and

the solvent was evaporated under vacuum to give an orange-

red solid (220 mg, 60%). ¹H NMR (C₆D₆): δ 7.18 (s, 4 H), 5.00

(s, 2 H, NCdCHsCN), 2.07 (s, 24 H), 0.09 (s, 18 H), -0.36 (s,

4 H, HfCH₂). Gated-{¹H}-¹³C NMR (C₆D₆) δ: 159.5 (m, CdN),

134.8 (m, benzo-CN), 131.8 (d, J ) 7, benzo-CMe), 126.3 (dd,

J ) 157, 5, benzo-CH), 103.9 (dm, J ) 157, CNsCHdCN),

47.9 (t, J ) 100, CH₂), 23.4 (t, J ) 100, CH₃), 19.9 (qd, J )

126, 5, CH₃), 4.1 (qm, J ) 116, SiMe).

(Me₈ta a )HfMe₂(4b). A solution of MeLi in Et₂O (1.4 M,

1.2 mL, 1.7 mmol) was added over 15 min to a slurry of 2b

(543 mg, 0.838 mmol) in toluene (60 mL). The mixture was

stirred for 1.5 h and centrifuged. The supernatant was

decanted off and evaporated under vacuum. The resulting

orange solid was slurried in toluene (25 mL) and centrifuged.

The supernatant was decanted off, and this process was

repeated 7 times. The combined supernatants were evapo-

rated under vacuum, and the resulting orange solid was

washed with pentane (3 × 5 mL) and dried under high vacuum

for 1 h (385 mg, 76%). This complex is only sparingly soluble

in C₆D₆and slowly decomposes to 2b in chlorinated solvents.

¹H NMR (C₆D₆): δ 7.08 (s, 4 H), 5.06 (s, 2 H, NCdCHsCN),

2.10 (s, 12 H), 1.97 (s, 12 H), -0.03 (br s, 6 H, HfCH₃). ¹H

NMR (C₂D₂Cl₄): δ 7.11 (s, 4 H), 5.24 (s, 2 H, NCdCHsCN),

2.38 (s, 12 H), 2.29 (s, 12 H), -1.24 (s, 6 H, HfCH₃). {¹H}¹³C

NMR (C₂D₂Cl₄): δ 157.5 (CdN), 133.6 (benzo-CN), 128.2

(benzo-CMe), 123.8 (benzo-CH), 101.1 (NCdCHsCN), 33.3

(HfCH₃), 22.0, 18.8. This NMR sample reacted overnight to

give 2b as the sole product. Anal. Calcd for C₂₈H₃₆HfN₄: C,

55.39; H, 5.98; N, 9.23. Found: C, 55.61; H, 6.02; N, 8.99.

(Me₉ta a )Zr (Me)(Et₂O) (5). A solution of MeLi (1.4 M, 0.70

mL, 0.98 mmol) in Et₂O was added to a slurry of 2a (0.28 g,

0.50 mmol) in Et₂O at -100 °C. The slurry was warmed to

23 °C and stirred overnight. The solvent was evaporated

under vacuum, and the residue was extracted with pentane

(3 × 25 mL). The combined extracts were evaporated under

vacuum, giving an orange solid (0.26 g, 87%). ¹H NMR

(C₆D₆): δ 6.62 (s, 2 H, benzo-CH), 6.61 (s, 2 H, benzo-CH),

4.72 (s, 2 H, NCdCHsCN), 2.92 (m, 4 H, Et₂O), 2.24 (br s, 6

H, 2 Me), 2.22 (s, 3 H, Me), 1.90 (s, 6 H, 2 Me), 1.85 (s, 6 H, 2

Me), 1.53 (s, 6 H, 2 Me), 0.14 (s, 3 H, ZrMe); the remaining

Et₂O resonance is obscured by resonances for excess pentane.

The reaction of isolated 3b with THF yields a product with a

similar NMR spectrum.

(Me₈ta a )Zr (NMe₂)₂(6a ). A slurry of Zr(NMe₂)₄(1.00 g,

3.74 mmol) and (Me₈taa)H₂(1.50 g, 3.74 mmol) in toluene (50

mL) was stirred at 23 °C for 1 h. The volatiles were removed

under vacuum, yielding a red solid which was dried under high

vacuum overnight. This solid was dissolved in toluene (10

mL), and pentane (10 mL) was layered on carefully and

allowed to slowly diffuse at -40 °C for 24 h, which resulted in

the formation of a red precipitate. This product was collected

by filtration, washed with pentane (5 × 10 mL), and dried

under high vacuum for 12 h (1.94 g, 90%). ¹H NMR (C₆D₆): δ

7.18 (s, 4 H), 5.07 (s, 2 H, NCdCHsCN), 2.86 (s, 12 H) NMe,

2.11 (s, 12 H, Me), 2.05 (s, 12 H, Me). Gated-{¹H}-¹³C NMR

(C₆D₆): δ 158.6 (m, CdN), 135.4 (m, benzo-CN), 133.1 (m,

benzo-CMe), 125.4 (dm, J ) 157, benzo-CH), 103.0 (dm, J )

151, NCdCHsCN), 45.5 (qq, J ) 129, 6, NCH₃), 22.8 (qd, J )

127, 5, CH₃), 19.8 (qd, J ) 125, 5, CH₃). Anal. Calcd for

C

₃₀H₄₂N₆Zr: C, 62.35; H, 7.32; N, 14.54. Found: C, 62.15; H,

7.10; N, 14.34.

(Me₈ta a )Zr (NEt₂)₂(6b). A solution of Zr(NEt₂)₄(1.00 g,

2.63 mmol) in toluene (10 mL) was transferred by cannula to

a solution of (Me₈taa)H₂(1.05 g, 2.63 mmol) in toluene (25 mL).

The mixture was stirred at 60 °C for 48 h under N₂. The

solvent was evaporated under vacuum to yield a red solid,

which was slurried in toluene (10 mL) and filtered. The

filtrate was cooled to -40 °C for 12 h to afford red crystals,

which were collected by filtration and washed with pentane

(5 mL). The combined mother liquor and washes were cooled

to -40 °C to give a second crop of red crystals. Both solids

were dried under vacuum overnight. Total yield: 0.973 g

(58.3%). ¹H NMR (C₆D₆): δ 7.11 (s, 4 H), 5.02 (s, 2H,

NCdCHsCN), 3.22 (q, J ) 6.9, 8 H, NCH₂CH₃), 2.10 (s, 12 H,

Me), 2.09 (s, 12 H, Me), 0.87 (t, J ) 6.9, 12 H, NCH₂CH₃).

Gated-{¹H}-¹³C NMR (C₆D₆): δ 158.6 (m, CdN), 136.4 (m,

benzo-CN), 133.2 (m, benzo-CMe), 125.8 (dm, J ) 166, benzo-

CH), 102.7 (dm, J ) 156, NCdCHsCN), 45.2 (tm, J ) 130,

NCH₂CH₃), 23.0 (qd, J ) 126, 4, Me), 19.9 (qd, J ) 125, 5,

Me), 16.0 (qm, J ) 123, NCH₂CH₃). Anal. Calcd for C₃₄H₅₀N₆-

Zr: C, 64.41; H, 7.95; N, 13.25. Found C, 64.64; H, 7.92; N,

13.01.

Rea ction of (Me₈ta a )Zr (NMe₂)₂w ith CH₂Cl₂. A solution

of 6a (0.020 g, 0.035 mmol) in CD₂Cl₂(0.5 mL) was maintained

at 23 °C and monitored by ¹H NMR. (Me₈taa)Zr(Cl)(NMe₂)

(7) was cleanly formed (>90%) in ca. 5 h. ¹H NMR (CD₂Cl₂):

δ 7.25 (s, 4 H, benzo-C-H), 5.43 (s, 2 H, NCdCHsCN), 2.38

(s, 12 H, Me), 2.35 (s, 12 H, Me), 2.20 (s, 6 H, NMe). A singlet

at δ 2.18 (6 H) for the organic byproduct CD₂(NMe₂)₂was also

observed. ¹H NMR (CD₂Cl₂, -90 °C): δ 7.23 (s, 4H, benzo-

CH), 5.47 (br s, ν_1/2) 30 Hz, 2H, NCdCHsCN), 2.36 (s, 12 H,

Me), 2.29 (s, 12 H, Me), 2.08 (s, 12 H, NMe and CD₂(NMe₂)₂).

{¹H}¹³C NMR (CD₂Cl₂): δ 158.6 (CdN), 136.5 (benzo-CN),

129.9 (benzo-CMe), 126.0 (benzo-CH), 103.8 (NCdCHsCN),

45.6 (NMe), 20.4 (Me). A signal at δ 43.3 for CD₂(NMe₂)₂was

also observed. After 14 h, 7 was completely transformed into

2a . At this point, the signal at δ 2.18 integrated for 12 H.

In a parallel reaction, a solution of (Me₈taa)Zr(NMe₂)₂(6a ,

0.276 g, 0.477 mmol) in CH₂Cl₂(10 mL) was stirred at 23 °C

for 24 h. The volatiles were vacuum-transferred to another

flask, and the remaining solid was dried overnight (2a , 0.250

g, 93.5% yield). The NMR spectra of the volatiles contained

resonances for CH₂(NMe₂)₂, which were identical to those of

an authentic sample (Aldrich). ¹H NMR (CD₂Cl₂): δ 2.17 (s,

12 H), 2.64 (s, 2 H). Gated-{¹H}-¹³C NMR (CD₂Cl₂): δ 83.8

(tm, J ) 137), 43.3 (qm, J ) 132). Resonances for CH₂Cl₂were

also observed.

[(Me₈ta a )Zr (µ-ΝMe₂)₂AlMe₂][AlMe₄] (8). A solution of

Al₂Me₆(66.5 µL, 0.346 mmol) in benzene (1 mL) was added to

a rapidly stirred solution of 6a (0.200 g, 0.346 mmol) in

benzene (2 mL). The color changed instantaneously from red

to yellow, and a yellow precipitate formed. Pentane (3 mL)

was added to the mixture, and the solid was isolated by

filtration (122 mg, 48.8%). ¹H NMR (CD₂Cl₂): δ 7.46 (s, 4 H,

Synthesis of (Me₈taa)MX₂and (Me₈taa)MX⁺Complexes

Organometallics, Vol. 17, No. 3, 1998 395

benzo-CH), 5.78 (s, 2 H, CNdCHsCN), 2.57 (s, 12 H, Me), 2.48

(s, 12 H, Me), 1.83 (s, 12 H, Me), -1.22 (1:1:1:1:1:1 sextet, J )

6.3 Hz, 12 H, AlMe₄^-), -1.72 (s, 6 H, AlMe₂). Gated-{¹H}-

¹³C NMR (CD₂Cl₂): δ 161.0 (m, CdN), 140.4 (m, benzo-CN),

127.9 (d, J ) 7, benzo-CMe), 127.6 (dq, J ) 159, 5, benzo-CH),

107.1 (d of septet, J ) 161, 4, NCdCHsCN), 44.1 (qq, J )

134, 6, NMe), 24.0 (qd, J ) 128, 4, Me), 20.5 (qd, J ) 127, 5,

Me), -5.2 (m, J _C-Al) 72, J _C-H) 106, AlMe₄^-), -14.6 (q, J )

111, AlMe₂). Anal. Calcd for C₃₆H₆₀Al₂N₆Zr: C, 59.88; H, 8.38;

N, 11.64. Found C, 59.78; H, 8.11; N, 11.44.

high vacuum overnight to afford 10c as a golden solid, which

contained 1.9 equiv of benzene (0.408 g, 61.8%). ¹H NMR

(CD₂ClCD₂Cl): δ 7.56 (s, 4 H, benzo-H), 5.72 (s, 2 H,

NCdCHsCN), 2.54 (s, 12 H, CH₃), 2.47 (s, 12 H, CH₃), 0.14

(s, 9 H, CH₂C(CH₃)₃), -0.51 (s, 2 H, ZrCH₂). The resonance

of benzene was also observed. Gated-{¹H}-¹³C NMR (CD₂Cl-

CD₂Cl): δ 161.7 (m, CdN), 141.5 (m, benzo-CN), 128.6 (dm,

J ) 161, benzo-CH), 126.6 (d, J ) 7, benzo-CMe), 107.5 (dm,

J ) 161, NCdCHsCN), 79.1 (tm, J ) 107, ZrCH₂), 33.5 (m,

CH₂CMe₃), 33.4 (qm, J ) 123, CH₂CMe₃), 22.9 (qd, J ) 122, 4,

CH₃), 20.2 (q, J ) 128,CH₃).

[(Me₈ta a )HfMe][B(C₆F ₅)₄] (10d ). This complex was gen-

erated in situ by the following procedure. An NMR tube was

charged with 4b (24.4 mg, 40.2 µmol) and [HNMe₂Ph]-

[B(C₆F₅)₄] (32.1 mg, 37.2 µmol), and CD₂Cl₂(0.5 mL) was added

by vacuum transfer at -78 °C. The tube was sealed and

warmed to 23 °C, and a homogeneous orange solution formed.

The NMR yield of 11c was 87%. ¹H NMR (CD₂Cl₂): δ 7.51 (s,

4 H), 5.77 (s, 2 H, NCdCHsCN), 2.59 (s, 12 H), 2.48 (s, 12 H),

-1.11 (s, 3 H, HfCH₃); resonances for free NMe₂Ph and CH₄

were also observed. {¹H}¹³C NMR (CD₂Cl₂): δ 163.0 (CdN),

141.1 (benzo-CN), 129.5, 126.1, 108.3 (NCdCHsCN), 46.6

(HfCH₃), 23.3, 20.4; resonances for free NMe₂Ph were also

observed.

[(Me₈ta a )Zr (µ-ΝMe₂)₂AlMe₂][B(C₆F ₅)₄] (9). This complex

was generated in NMR-scale reactions. An NMR tube was

charged with 8 (0.015 g, 0.021 mmol) and [HNMePh₂][B(C₆F₅)₄]

(0.018 g, 0.021 mmol). CD₂Cl₂(0.5 mL) was added by vacuum

transfer at -78 °C. Gas evolution was observed. The tube

1

was warmed to 23 °C, and a H NMR spectrum was obtained.

¹H NMR (23 °C): Signals for 9 δ 7.44 (s, 4 H), 5.74 (s, 2 H),

2.54 (s, 12 H), 2.47 (s, 12 H), 1.82 (s, 12 H), -1.72 (s, 6 H);

Signals for NMePh₂δ 7.29 (t, J ) 7.9, 4 H), 7.08 (d, J ) 7.9,

4 H), 7.02 (t, J ) 7.9, 2 H), 3.30 (s, 3 H); Signal for Al₂Me₆δ

-0.48 (s). The solvent was removed under vacuum to afford

a foamy solid, which was washed with benzene and pentane

and dried under vacuum overnight. Fresh CD₂Cl₂(0.5 mL)

was added to the tube at -78 °C. The ¹H NMR spectrum of

this sample contained only resonances for 9.

[(Me₈t a a )Zr (CH₂SiMe₃)(P Me₂P h )][BP h ₄] (11a ). Solid

[HNBu₃][BPh₄] (118 mg, 0.233 mmol) was added to a solution

of 3a (159 mg, 0.239 mmol) and PMe₂Ph (36 µL, 0.25 mmol)

in 1,2-dichloroethane (10 mL). The mixture was stirred for

15 min and concentrated under vacuum to 2 mL. Pentane (10

mL) was added, and the mixture was stirred until a yellow

solid formed. The solid was isolated by filtration and dried

under high vacuum overnight (192 mg, 77%). ¹H NMR (CD₂-

Cl₂): δ 7.44 (t, J ) 7, 1 H, p-Ph), 7.28 (s, ca. 4 H), 6.97 (t, J )

7, 2 H, m-Ph), 5.60 (s, 2 H, NCdCHsCN), 2.44 (s, 12 H), 2.43

(s, 12 H), 1.16 (br s, 6 H), -0.46 (s, 9 H), -1.00 (s, 2 H, ZrCH₂);

[(Me₈ta a )Zr (η²-CH₂P h )][B(C₆F ₅)₄] (10a ). A flask was

charged with 3c (0.100 g, 0.149 mmol) and [HNMePh₂][B(C₆F₅)₄]

(0.131 g, 0.151 mmol), and CH₂Cl₂(5 mL) was added by

vacuum transfer at -78 °C. The mixture was allowed to warm

to 23 °C and was stirred for 10 min. The volatiles were

evaporated under vacuum, yielding a yellow-orange solid.

Toluene (5 mL) was added, resulting in an orange-red oil. The

mixture was stirred for 1 min, and the supernatant was

decanted off. This procedure was repeated 3 times and then

once with pentane. The oil was dried under vacuum overnight,

yielding [(Me₈taa)ZrCH₂Ph][B(C₆F₅)₄]‚2toluene as an orange

solid (0.180 g, 83.6%). ¹H NMR (CD₂Cl₂): δ 7.34 (s, 4 H, benzo-

CH), 6.90 (t, J ) 7.7, 2H, m-Ph), 6.82 (t, J ) 7.2, 1 H, p-Ph),

5.64 (s, 2 H, NCdCHsCN), 5.01 (d, J ) 7.1, 2 H, o-Ph), 2.50

(s, 12 H, Me), 2.49 (s, 12 H, Me), 0.94 (s, 2 H, CH₂Ph).

Resonances for toluene (2 equiv) were also observed. Gated-

{¹H}-¹³C NMR (CD₂Cl₂): δ 161.1 (m, CdN), 141.2 (m, ipso-

CH₂Ph), 139.1 (m, benzo-CN), 132.3 (d, J ) 158.7, o-CH₂Ph),

128.7 (dm, J ) 158, benzo-CH), 125.9 (d, J ) 6, benzo-CMe),

124.1 (overlapping dm, p- and m-CH₂Ph), 106.8 (d of septets,

J ) 161, 4, NCdCHsNC), 60.6 (tt, J ) 136, 3, CH₂Ph), 23.2

(qd, J ) 128, 4, Me), 20.5 (qd, J ) 127, 5, Me). Resonances

-

the o-Ph resonance of PMe₂Ph was obscured by the BPh₄

resonances. {¹H}¹³C NMR (CD₂Cl₂): δ 161.2 (C)N), 140.3

(benzo-CN), 130.5 (d, J _CP) 12, PMe₂Ph), 130.1 (br, PMe₂Ph),

129.0 (d, J _CP) 8, PMe₂Ph), 127.4 (benzo-CH), 126.8 (benzo-

CMe), 106.2 (NCdCHsCN), 49.6 (ZrCH₂), 23.2, 20.5, 12.9 (br

d, J _CP) 3, PMe₂Ph), 2.5; the ipso-C of PMe₂Ph was not

observed. Anal. Calcd for C₆₂H₇₂BN₄PSiZr: C, 71.99; H, 7.02;

N, 5.42. Found: C, 71.80; H, 6.78; N, 5.61.

[(Me₈ta a )Zr (CH₂SiMe₃)(THF )_n][BP h ₄] (11b). This com-

plex was generated in situ in 76% NMR yield by the following

procedure. An NMR tube was charged with 3a ‚0.5toluene (9.0

mg, 14 µmol) and [HNBu₃][BPh₄] (7.1 mg, 14 µmol), and CD₂-

Cl₂(ca. 0.5 mL) was added by vacuum transfer at -78 °C.

The tube was immediately cooled to -196 °C, and THF (1.6

equiv) was condensed in. The tube was sealed and warmed

to 23 °C, and a homogeneous orange solution formed. ¹H NMR

(CD₂Cl₂): δ 7.42 (s, 4 H), 5.62 (s, 2 H, NCdCHsCN), 3.39 (br

m, THF), 2.46 (s, 24 H, both sets of 4 Me’s are coincident),

1.75 (m, THF), -0.54 (s, 9 H), -1.02 (s, 2 H, ZrCH₂);

resonances for SiMe₄and free NBu₃were also observed.

for toluene were also observed. Anal. Calcd for C₅₇H₃₇

-

BF₂₀N₄Zr^.2C₇H₈: C, 59.05; H, 3.70; N, 3.88. Found: C, 59.33,

H, 3.47; N, 3.81.

[(Me₈ta a )Zr CH₂SiMe₃][B(C₆F ₅)₄] (10b). This complex

was generated in situ by the following procedure. Attempts

to isolate 10b in larger-scale reactions were unsuccessful. An

NMR tube was charged with 3a (31.7 mg, 47.7 µmol) and

[HNMe₂Ph][B(C₆F₅)₄] (38.3 mg, 44.4 µmol), and C₂D₂Cl₄(0.5

mL) was added by vacuum transfer at -78 °C. The tube was

sealed and warmed to 23 °C. A slightly turbid orange solution

formed. The NMR yield of 9 was 80%. ¹H NMR (C₂D₂Cl₄): δ

7.51 (s, 4 H), 5.72 (s, 2 H, NCdCHsCN), 2.55 (s, 12 H), 2.48

(s, 12 H), -0.67 (s, 9 H), -0.87 (s, 2 H, ZrCH₂); resonances for

free NMe₂Ph and SiMe₄were also observed. Gated-{¹H}-¹³C

NMR (C₂D₂Cl₄): δ 159.8 (m, CdN), 139.9 (d, J ) 5, benzo-

CN), 126.4 (dd, J ) 161, 5, benzo-CH), 124.4 (d, J ) 6, benzo-

CMe), 106.4 (d, J ) 162, NCdCHsCN), 53.0 (t, J ) 107,

ZrCH₂), 21.4 (q, J ) 123), 18.8 (q, J ) 129), -1.4 (q, J ) 118);

resonances for free NMe₂Ph and SiMe₄were also observed.

[(Me₈ta a )Zr CH₂CMe₃][B(C₆F ₅)₄] (10c). A mixture of 3d

(0.300 g, 0.475 mmol) and [HNMePh₂][B(C₆F₅)₄] (0.410 g, 0.475

mmol) in benzene (10 mL) was stirred for 15 min at 23 °C. A

red oil separated. The supernatant was decanted off, and the

oil was washed with benzene (2 × 10 mL) and dried under

[(Me₈ta a )Zr (CH₂P h )(THF )][B(C₆F ₅)₄] (11c). This species

was generated in situ and characterized by ¹H NMR. THF

(0.75 equiv) was added to a solution of [(Me₈taa)Zr(CH₂Ph)]-

[B(C₆F₅)₄] (0.15 mmol) in CD₂Cl₂(0.5 mL), and the ¹H NMR

spectrum was recorded at -80 °C. Separate resonances for

(Me₈taa)Zr(CH₂Ph)(THF)⁺and (Me₈taa)Zr(CH₂Ph)⁺were ob-

served. A single set of resonances was observed at ambient

temperature, indicating that THF exchange is fast on the NMR

time scale under these conditions. Addition of excess THF (4.9

equiv total) did not change the spectrum of (Me₈taa)Zr(CH₂-

Ph)(THF)⁺. ¹H NMR (CD₂Cl₂, -80 °C): δ 7.28 (s, 2 H, benzo-

H), 6.95 (t, J ) 7.4, 2 H, meta-benzyl), 6.93 (s, 2 H, benzo-H),

6.68 (t, J ) 7.4, 1 H, para-benzyl), 6.07 (d, J ) 7.8, 2 H, ortho-

benzyl), 5.70 (s, 1 H, NCdCHsCN), 5.46 (s, 1 H, NCdCHsCN),

3.17 (br m, 4 H, THF), 2.39 (s, 6 H, Me), 2.36 (s, 6 H, Me),

396 Organometallics, Vol. 17, No. 3, 1998

Martin et al.

2.34 (s, 6 H, Me), 2.33 (s, 6 H, Me), 1.67 (br m, 4 H, THF),

0.66 (s, 2 H, ZrCH₂).

(m, benzo-CN), 138.3 (m, benzo-CN), 136.2 (m, benzo-CMe),

127.6 (m, benzo-CMe), 126.7 (dm, J ) 154, benzo-CH), 120.8

(dm, J ) 157, benzo-CH), 107.3 (d, J ) 161, NCdCHsCN),

90.2 (d, J ) 161, NCdCHsCN), 23.1 (qd, J ) 129, 4, Me), 22.4

(qd, J ) 129, 3, Me), 20.8 (qd, J ) 127, 5, Me), 19.9 (qd, J )

126, 5, Me). Anal. Calcd for C₅₀H₃₁BF₂₀N₄OZr: C, 50.64; H,

2.63; N, 4.72. Found: C, 50.39; H, 2.62; N, 4.47.

[(Me₈ta a )Hf(CH₃)(THF )][B(C₆F ₅)₄] (11d ). Excess THF

(4.9 equiv) was added to a solution of 10d in CD₂Cl₂, and ¹H

NMR spectra were recorded. ¹H NMR (CD₂Cl₂, -90 °C, fast

exchange of free and coordinated THF): δ 7.21 (s, 4 H), 5.51

(s, 2 H), 3.53 (br, THF), 2.41 (s, 12 H), 2.31 (s, 12 H), 1.73 (br,

THF), -1.36 (s, 3 H).

[{(Me₈ta a )Zr (µ-OEt)}₂][B(C₆F ₅)₄]₂(14b). Ethanol (5.7 µL,

0.095 mmol) was added by syringe to a solution of 10a ‚C₆H₆

(0.144 g, 0.095 mmol) in CH₂Cl₂(5 mL). The color of the

solution changed from orange to yellow in a few seconds. The

reaction mixture was stirred at 23 °C for 30 min. The volatiles

were removed under vacuum to afford a yellow solid, which

was dried under vacuum for 12 h. The solid was recrystallized

from CH₂Cl₂/pentane (0.083 g, 72%). ¹H NMR (CD₂Cl₂): δ 7.41

(s, 4 H, benzo-CH), 6.87 (s, 4 H, benzo-CH), 5.69 (s, 2 H,

CNsCHdCN), 4.31 (s, 2 H, CNsCHdCN), 2.77 (q, J ) 7.0, 4

H, OCH₂), 2.72 (s, 12 H, Me), 2.55 (s, 12 H, Me), 2.39 (s, 12 H,

Me), 2.18 (s, 12 H, Me), 0.47 (t, J ) 7.0, 6 H, CH₂CH₃). Gated-

{¹H}-¹³C NMR (CD₂Cl₂): δ 161.8 (m, CdN), 157.5 (m, CdN),

140.5 (m, benzo-CN), 137.7 (m, benzo-CMe), 136.3 (m, benzo-

CN), 127.3 (m, benzo-CMe), 126.6 (dd, J ) 158, 4, benzo-CH),

121.0 (dd, J ) 163, 4, benzo-CH), 107.3 (dm, J ) 162,

NCdCHsCN), 90.8 (dm, J ) 160, NCdCHsCN), 66.0 (tm, J

) 143, OCH₂), 23.4 (qd, J ) 129, 4, Me), 23.0 (qd, J ) 128, 4,

Me), 20.9 (qd, J ) 127, 5, Me), 20.0 (qd, J ) 126, 5, Me), 17.7

(q, J ) 125, CH₂CH₃). Anal. Calcd for C₅₂H₃₅BF₂₀N₄OZr: C,

51.45; H, 2.91; N, 4.62. Found: C, 50.51; H, 2.64; N, 4.44.

Olefin P olym er ization with 10a. (i) Method 1: A Fisher-

Porter bottle was charged with toluene (400 mL), Al(ⁱBu)₃(150

µL, 0.58 mmol) if desired, and 10a ‚1.8C₆H₆(0.040 g, 0.029

mmol). The bottle was thermostatted at 50 °C, charged with

ethylene (1.3 atm), and vigorously stirred. After 17-24 h,

EtOH (1 L) was added and the polymer was isolated by

filtration, washed with EtOH and H₂O, and dried under

vacuum. Without Al(ⁱBu)₃: yield 0.27 g, activity ) 300 (g of

PE)(mol of cat.)^-1atm^-1h^-1; M_w) 99 300, M_n) 38 500, M_w/

M_n) 2.6; linear by NMR, benzyl end groups not detected. With

Al(ⁱBu)₃: yield 0.35 g, activity ) 550 (g of PE) (mol of cat.)^-1

atm^-1h^-1. (ii) Method 2: A flask was charged with chloroben-

zene (5 mL), Al(ⁱBu)₃(150 µL, 0.58 mmol), and 10a ‚1.8C₆H₆

(0.040 g, 0.029 mmol) in the drybox and then attached to a

high-vacuum line. The flask was degassed by freeze-pump-

thaw cycles, exposed to 1 atm of ethylene, and heated to 90

°C. After 17 h, the reaction was quenched with EtOH/HCl

and the polymer was isolated as described above. Yield 0.20

g, activity ) 400 (g of PE) (mol of cat.)^-1atm^-1h^-1; M_w) 1,-

1

410, M_n) 800, M_w/M_n) 1.8; H NMR ratio of saturated end

[(Me₈ta a )HfCMedCMeCMedCMe₂][B(C₆F ₅)₄] (15).

A

groups/vinyl end groups ) 13/1, M_n) 786; ¹³C NMR saturated

end groups detected, no branching detected. (iii) Control

experiment: Using conditions and procedures similar to those

outlined in method 1, an activity of 48 000 (g of PE)(mol of

cat.)^-1atm^-1h^-1was measured for Cp₂ZrMe₂/[HNMePh₂]-

[B(C₆F₅)₄]/Al(iBu)₃.

solution of 4b (106 mg, 0.175 mmol), [HNMe₂Ph][B(C₆F₅)₄] (139

mg, 0.161 mmol), and 2-butyne (1.1 mmol) in CH₂Cl₂(4 mL)

was stirred for 1 day at 23 °C, and the volatiles were removed

under vacuum. The residue was dissolved in CH₂Cl₂(3 mL),

and the solution was filtered and concentrated under vacuum

to 1 mL. Pentane was added, and a brown, oily solid was

isolated by filtration and dried under high vacuum for 1 day

(172 mg, 78%). ¹H NMR (CD₂Cl₂): δ 7.40 (s, 4 H), 5.64 (s, 2

H, NCdCHsCN), 2.52 (s, 12 H), 2.44 (s, 12 H), 1.60 (s, 3 H),

1.51 (s, 3 H), 1.13 (s, 3 H), 1.10 (s, 3 H), 0.90 (s, 3H). {¹H}¹³C

NMR (CD₂Cl₂): δ 214.0 (HfC), 163.1 (CdN), 147.1, 141.6, 139.1

(benzo-CN), 135.5, 128.7 (benzo-CMe), 127.0 (benzo-CH), 107.4

(NCdCHsCN), 23.9 (4 Me), 23.7, 22.1, 20.9, 20.2 (4 Me), 17.5,

14.5. Anal. Calcd for C₅₉H₄₅BF₂₀HfN₄: C, 51.38; H, 3.29; N,

4.06. Found: C, 51.11, H, 3.49; N, 4.06.

[(Me₈t a a )Zr (OCMe₂CH ₂CH ₂CH dCH ₂)][B(C₆F ₅)₄] (13).

The alcohol HOCMe₂CH₂CH₂CHdCH₂(26.4 µL, 0.220 mmol)

was added in 3 portions to a slurry of 10a ‚1.3C₆H₆(0.300 g,

0.194 mmol) in benzene (5 mL). A pale orange oil separated.

The supernatant was decanted off, and the oil was washed

with benzene (5 mL). Hexane (20 mL) was added, and the

mixture was stirred, which resulted in the formation of a

yellow solid. The solid was collected by filtration, washed with

hexane (2 × 10 mL), and dried under vacuum (0.220 g, 88%).

¹H NMR (CD₂Cl₂): δ 7.45 (s, 4 H, benzo-CH), 5.69 (s, 2 H,

CNsCHdCN), 5.40 (ddt, J ) 17.0, 10.3, 10.1, 1 H, -H₂CdCH),

4.76 (dm, J ) 10.2, 1 H, cis-HHCdCH), 4.69 (dq, J ) 17.0,

1.8, 1 H, trans-HHCdCH), 2.53 (s, 12 H, Me), 2.45 (s, 12 H,

Me), 1.18 (m, 2 H, CH₂), 0.75 (m, 2 H, CH₂), 0.38 (s, 6H, Me).

Resonances for toluene were also observed. Gated-{¹H}-¹³C

NMR (CD₂Cl₂): δ 162 (m, CdN), 140.5 (m, benzo-CN), 139.7

(d, overlapped with B(C₆F₅)₄^-resonance, CHdCH₂), 127.8 (m,

benzo-CMe), 127.1 (dm, J ) 159, benzo-CH), 113.7 (tm, J )

154, CHdCH₂), 107.1 (d, J ) 160, NCdCHsCN), 80.5 (m,

C-O), 42.4 (tm, J ) 122, CH₂), 30.0 (qm, J ) 125, Me), 28.5

(tm, J ) 124, CH₂), 22.8 (qd, J ) 128, 4, Me), 20.3 (qd, J )

127, 5, Me). ¹⁹F NMR (CD₂Cl₂) δ -132.8 (br s, 8 F), -163.6 (t,

J _FF) 20.3, 4F), -167.4 (br t, 8 F).

[(Me₈ta a )Hf(C(SiMe₃)dCMe₂)][B(C₆F ₅)₄] (16). A frozen

CH₂Cl₂solution (5 mL) of 4b (99.9 mg, 0.165 mmol) and

[HNMe₂Ph][B(C₆F₅)₄] (131 mg, 0.152 mmol) was exposed to

1-Me₃Si-1-propyne (0.9 mmol) at -196 °C and warmed to 23

°C. The orange solution was stirred for 1.5 h and concentrated

under vacuum to 3 mL. Pentane was added, resulting in the

formation of a red oil. The supernatant was decanted off, and

the oil was briefly dried under vacuum to give an orange solid,

which was washed with pentane and dried under high vacuum

for 2 days. ¹H NMR analysis indicated the presence of pentane

(0.72 equiv). Yield: 175 mg, 80%. Low-temperature NMR

spectra establish that 16 adopts a C_s-symmetric structure.

1

However, at 23 °C, the H and ¹³C NMR spectra of 16 exhibit

broadened and/or coalesced resonances, indicative of a dynamic

process which results in effective C_2vsymmetry. ¹H NMR

(CD₂Cl₂, -20 °C): δ 7.42 (s, 2 H), 7.41 (s, 2 H), 5.81 (s, 1 H,

NCdCHsCN), 5.73 (s, 1 H, NCdCHsCN), 2.57 (s, 6 H), 2.56

(s, 6 H), 2.43 (2 s, 2 × 6 H), 1.36 (s, 3 H), 1.33 (s, 3 H), -0.52

(s, 9 H). {¹H}¹³C NMR (CD₂Cl₂, -20 °C): δ 202.3 (HfC), 166.5

(dCMe₂), 162.6 (CdN), 162.5 (CdN), 140.4 (benzo-CN), 140.2

(benzo-CN), 127.3 (benzo-CH), 126.9 (benzo-CH), 126.1 (ben-

zo-CMe), 125.8 (benzo-CMe), 108.1 (NCdCHsCN), 107.7

(NCdCHsCN), 29.2 (1 Me), 26.9 (1 Me), 23.2 (4 Me), 20.3 (2

[{(Me₈ta a )Zr (µ-OH)}₂][B(C₆F ₅)₄]₂(14a ). Water (1.2 µL,

0.066 mmol) was added by syringe to a solution of 10a ‚1.8C₆H₆

(0.105 g, 0.066 mmol) in CH₂Cl₂(1 mL). The solution was

stirred for 2 min and cooled to -78 °C. Pentane (2 mL) was

added, and an orange oil separated. The supernatant was

removed by cannula, and the oil was dried under vacuum,

affording a yellow solid (0.058 g, 74%). The solid was

recrystallized from CH₂Cl₂/pentane and dried under vacuum.

¹H NMR (CD₂Cl₂): δ 7.39 (s, 4 H, benzo-CH), 6.88 (s, 4 H,

benzo-CH), 5.60 (s,

2 H, CNsCHdCN), 4.14 (s, 2 H,

Me), 20.1 (2 Me), -0.1 (SiMe₃). Anal. Calcd for C₅₇H₄₅

-

CNsCHdCN), 3.09 (s, 2 H, OH), 2.70 (s, 12 H, Me, 2.46 (s, 12

H, Me), 2.40 (s, 12 H, Me), 2.20 (s, 12 H, Me). Gated-{¹H}-

¹³C NMR (CD₂Cl₂): δ 161.5 (m, CdN), 157.8 (m, CdN), 140.2

BF₂₀HfN₄Si: C, 49.49; H, 3.28; N, 4.05. Found: C, 48.98; H,

3.73; N, 3.81. Duplicate analysis also gave a low C value

(48.89).

Synthesis of (Me₈taa)MX₂and (Me₈taa)MX⁺Complexes

Organometallics, Vol. 17, No. 3, 1998 397

[{(Me₈ta a )Zr (µ-CCP h )}₂][B(C₆F ₅)₄]₂(17a ). Phenylacety-

lene (3.2 µL, 0.29 mmol) was added by syringe to a solution of

10a ^.2toluene (0.208 g, 0.145 mmol) in CH₂Cl₂(5 mL). The

solution was stirred at 23 °C for 1 h, and the color changed

from orange to red. The volatiles were removed under vacuum

to yield a brown solid. The solid was taken up in benzene (10

mL), and the resulting slurry was filtered, affording a yellow

powder which was washed with hexane (2 × 10 mL) and dried

under vacuum overnight (0.140 g, 76.1%). The product was

further purified by recrystallization from CH₂Cl₂/pentane at

23 °C and CH₂Cl₂at -40 °C. ¹H NMR (CD₂Cl₂): δ 7.53 (s, 4

H, benzo-CH), 7.44 (t, J ) 7.9, 2 H, p-Ph), 7.28 (t, J ) 7.9, 4

H, m-Ph), 6.84 (s, 4 H, benzo-CH), 6.75 (d, J ) 8.4, 4 H, o-Ph),

5.25 (s, 2 H, NCdCHsCN), 4.09 (s, 2H, NCdCHsCN), 2.77-

(s, 12 H, Me), 2.38 (s, 12 H, Me), 2.28 (s, 12 H, Me), 2.17 (s, 12

H, Me). Gated-{¹H}-¹³C NMR (CD₂Cl₂): δ 160.2 (m, CdN),

157.2 (m, CdN), 141.2 (m, CCPh), 139.5 (d, J ) 7, benzo-CMe),

136.3 (m, benzo-CN), 135.4 (benzo-CN, overlapped with anion

resonance), 132.5 (dt, J ) 159, 6, o-Ph), 132.1 (dt, J ) 164, 7,

p-Ph), 129.2 (dd, J ) 163, 8, benzo-CH), 127.0 (dm, J ) 159,

benzo-CH), 125.6 (d, J ) 7, benzo-CMe), 121.8 (s, i-Ph), 121.0

(dm, J ) 158, m-Ph), 119.0 (t, J ) 8, CCPh), 107.4 (dm, J )

162, NCdCHsCN), 83.0 (dm, J ) 162, NCdCHsCN), 23.3

(qd, J ) 128, 4, Me), 22.1 (qd, J ) 129, 3, Me), 21.1 (qd, J )

127, 5, Me), 20.0 (qd, J ) 126, 5, Me). ¹⁹F NMR (CD₂Cl₂): δ

-132.8 (8 F), -163.5 (t, J _FF) 20.4, 4 F), 167.3 (br t, 8F). Anal.

Calcd for C₅₈H₃₅BF₂₀N₄Zr: C, 54.86; H, 2.78; N, 4.41. Found:

C, 54.93; H, 2.65; N, 4.33.

[{(Me₈taa)Zr (µ-CCP r )}₂][B(C₆F₅)₄]₂(17b). 1-Pentyne (163

mm, 50 mL, 23 °C; 0.44 mmol) was vacuum transferred into a

flask containing a frozen solution of 10a ‚1.2C₆H₆(0.198 g,

0.146 mmol) in CH₂Cl₂(5 mL) at -196 °C. The reaction

mixture was warmed to 23 °C and stirred for 21 h. The

volatiles were evaporated under vacuum to afford a yellow

solid, which was slurried in benzene (5 mL), filtered, and

washed with benzene (10 mL) and pentane (40 mL). The solid

was dried under vacuum for 12 h (0.167 g, 92%). ¹H NMR

(CD₂Cl₂): δ 7.36 (s, 2 H, benzo-CH), 6.89 (s, 2 H, benzo-CH),

5.70 (s, 1 H, CNsCHdCN), 4.13 (s, 1 H, CNsCHdCN), 2.70

(s, 6 H, Me), 2.43 (s, 6 H, Me), 2.35 (s, 6 H, Me), 2.19 (s, 6 H,

Me), 1.53 (t, J ) 7.2, 2H, CCCH₂), 0.94 (sextet, J ) 7.2,

CH₂CH₂CH₃), 0.61 (t, J ) 7.2, 3H, CH₂CH₂CH₃). Gated-{¹H}-

¹³C NMR (CD₂Cl₂): δ 160.2 (m, CdN), 156.9 (m, CdN), 141.6

(m, CCPr), 140.8 (m, benzo-CN), 139.2 (d, J ) 8 Hz, benzo-

CMe), 136.2 (m, benzo-CN), 126.8 (dd, J ) 160, 5, benzo-CH),

125.5 (d, J ) 6, benzo-CMe), 120.9 (dd, J ) 157, 4, benzo-CH),

115.0 (m, CCPr), 107.1 (dm, J ) 161, NCdCHsCN), 83.6 (dm,

J ) 162, NCdCHsCN), 23.2 (qd, J ) 125, 4, Me), 22.9 (tm, J

) 130, CH₂), 22.6 (overlapped, CH₂), 21.9 (qd, J ) 125, 3, Me),

21.0 (qd, J ) 127, 5, Me), 20.0 (qd, J ) 126, 5, Me), 13.6 (qm,

J ) 125, CH₂CH₃).

was added. The tube was sealed and warmed to 23 °C. The

¹H NMR spectrum indicated that 18a was formed in ca. 85%

NMR yield after 1 h. ¹H NMR (CD₂Cl₂, rapid PMe₃ex-

change): δ 7.46 (s, 4 H, benzo-CH), 7.13 (m, 3 H), 6.84 (m, 2

H), 5.74 (s, 2 H, NCdCHsCN), 2.55 (s, 12 H, Me), 2.46 (s,

12H, Me), 0.70 (br, 27 H, PMe₃). ¹H NMR (CD₂Cl₂, -93 °C,

slow PMe₃exchange): δ 7.33-7.32 (m, 3 H, benzo-CH and

p-Ph), 7.05-7.13 (m, 4 H, benzo-CH and m-Ph), 6.73 (d, J )

6.9, 2 H, o-Ph), 5.65 (s, 2 H, NCdCHsCN), 2.47 (s, 6 H, Me),

2.44 (s, 6 H, Me), 2.32 (s, 6 H, Me), 1.94 (s, 6 H, Me), 0.97 (d,

J ) 5, free PMe₃), 0.91 (s, 9 H, coordinated PMe₃). ¹³C{¹H}

NMR (CD₂Cl₂): δ 160.4, 140.8, 131.2, 128.5, 127.7, 126.9

(overlapped signals), 126.5, 125.3, 106.4, 23.1, 20.4, 14.5.

X-r a y Da ta Collection , Str u ctu r e Deter m in a tion , a n d

Refin em en t for [{(Me₈ta a )Zr (µ-OH)}₂][B(C₆F ₅)₄]₂(14a ). A

yellow single crystal was mounted on a fiber and transferred

to the goniometer. The crystal was cooled to -100 °C during

data collection by using a stream of cold nitrogen gas. The

space group was determined to be the centric P2₁/n from the

systematic absences. A summary of the data collection

parameters is given in Table 1.

One molecule of pentane per formula unit was found to be

disordered within the lattice. The refinement of these atoms

was poor, although at least two orientations of the molecule

were resolved. C101 was refined at full occupancy, C102 and

C103 at 75% occupancy, C104-C107 at 50% occupancy, and

C108 and C109 at 25% occupancy for a total of 5 C atom

positions. These atoms were refined isotropically only, and

no H atoms were included for these positions. Refinement of

non-hydrogen atoms (except for the disordered solvent mol-

ecule) was carried out with anisotropic temperature factors.

The geometrically constrained hydrogen atoms (except for the

disordered solvent molecule) were placed in calculated posi-

tions and allowed to ride on the bonded atom with B ) 1.2U_eqv

-

(C). The methyl H atoms (except for the disordered solvent

molecule) were included as a rigid group with rotational

freedom at the bonded carbon atom (B ) 1.2U_eqv(C)). The

remaining H atoms were not included in the final refinement.

The lack of resolution in the disordered solvent resulted in R

values which are higher than normal; however, the geometrical

parameters associated with 14a (Table 2) are quite good.

Ack n ow led gm en t. This work was supported by the

Department of Energy (Grant No. DE-FG02-88ER13935).

Alfredo Martin thanks the Ministedio de Educacio´n y

Ciencia (MEC) of Spain for a postdoctoral fellowship. A

gift of [HNMe₂Ph][B(C₆F₅)₄] from Boulder Scientific is

gratefully acknowledged.

Su p p or tin g In for m a tion Ava ila ble: Tables of data col-

lection parameters, atomic coordinates, bond lengths and bond

angles, anisotropic thermal parameters, and hydrogen atom

coordinates for 14a ‚pentane (20 pages). Ordering information

is given on any current masthead page.

[(Me₈ta a )Zr (CCP h )(P Me₃)][B(C₆F ₅)₄] (18a ). This com-

plex was generated in situ by the following procedure. An

NMR tube was charged with 17a (0.0237 g, 0.0093 mmol), and

CD₂Cl₂(0.5 mL) was added by vacuum transfer at -78 °C.

The mixture was cooled to -196 °C, and PMe₃(0.028 mmol)

OM970814X

Article Doi

Neutral and cationic group 4 metal compounds containing octamethyldibenzotetraazaannulene (Me8taa2-) ligands. Synthesis and reactivity of (Me8taa)MX2 and (Me8taa)MX+ complexes (M = Zr, Hf;

DOI: 10.1021/om970814x

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