Synthesis, structures, bonding, and ethylene reactivity of group 4 metal alkyl complexes incorporating 8-quinolinolato ligands

3282

Organometallics 1997, 16, 3282-3302

Syn th esis, Str u ctu r es, Bon d in g, a n d Eth ylen e Rea ctivity

of Gr ou p 4 Meta l Alk yl Com p lexes In cor p or a tin g

8-Qu in olin ola to Liga n d s

Xiaohong Bei, Dale C. Swenson, and Richard F. J ordan*

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

Received March 24, 1997^X

This contribution describes the synthesis, structures, bonding, and reactivity of neutral

(Ox)₂MR₂and cationic (Ox)₂MR⁺zirconium and hafnium alkyl complexes which contain

substituted 8-quinolinolato ligands (Ox^-) 2-Me-8-quinolinolato, MeOx^-, 2; 2-Me-5,7-Br₂-

8-quinolinolato, MeBr₂Ox^-, 3). Alkane elimination and halide displacement reactions provide

routes to (MeOx)₂ZrR₂(9a , R ) CH₂Ph; 9b, R ) CH₂CMe₃; 9c, R ) CH₂SiMe₃), (MeOx)₂-

Hf(CH₂Ph)₂(10a ), (MeBr₂Ox)₂ZrR₂(11a , R ) CH₂Ph; 11b, R ) CH₂CMe₃), (MeBr₂Ox)₂Hf-

(CH₂Ph)₂(14a ), (MeOx)₂ZrCl₂(15), (MeBr₂Ox)₂ZrCl₂(16), and (MeBr₂Ox)₂Zr(NMe₂)₂(17).

The reaction of 16, 17, or (MeBr₂Ox)₄Zr with AlMe₃yields (MeBr₂Ox)AlMe₂(18). An X-ray

crystallographic analysis shows that in the solid state 9a adopts a distorted octahedral

structure with a trans-O, cis-N, cis-R ligand arrangement and that one of the benzyl ligands

is bonded in an η²-fashion. Solution NMR data are consistent with this structure and

establish that exchange of the distorted and normal benzyl ligands is rapid on the NMR

time scale. Solution NMR data for the other (Ox)₂MR₂complexes are consistent with

analogous octahedral, trans-O, cis-N, cis-R structures for these species. Variable-temperature

NMR studies establish that (Ox)₂MR₂complexes undergo inversion of metal configuration

(i.e., Λ/∆ isomerization, racemization) on the NMR time scale at elevated temperatures (∆G^q

(racemization) ) 15-18 kcal/mol). Thermolysis of 11a results in migration of a benzyl ligand

from Zr to C2 of a MeBr₂Ox^-ligand, yielding (MeBr₂Ox)(2-Me-2-CH₂Ph-5,7-Br₂-Ox)ZrCH₂-

Ph (19) as a single diastereomer. Reaction of 9a or 9b with [HNMe₂Ph][B(C₆F₅)₄] yields

the base-free cationic complexes [(MeOx)₂Zr(R)][B(C₆F₅)₄] (20a , R ) CH₂Ph; 20b, R ) CH₂-

CMe₃), while the corresponding reaction of 11a yields the labile amine adduct [(MeBr₂Ox)₂Zr-

(CH₂Ph)(NMe₂Ph)][B(C₆F₅)₄] (21a ). The reaction of [HNMePh₂][B(C₆F₅)₄] with the appro-

priate (Ox)₂M(CH₂Ph)₂complex yields 20a , [(MeOx)₂Hf(CH₂Ph)][B(C₆F₅)₄] (22a ), or

[(MeBr₂Ox)₂M(CH₂Ph)][B(C₆F₅)₄] (23a , M ) Zr; 24a , M ) Hf). An X-ray crystallographic

analysis establishes that the cation of 23a adopts a square pyramidal structure with a highly

distorted (η²) benzyl ligand in the apical site and a trans-O, trans-N ligand arrangement in

the basal sites, and NMR studies show that 23a and 24a adopt analogous structures in

solution. In contrast, NMR studies establish that 20a , 20b, and 22a , which contain the

more strongly electron-donating MeOx^-ancillary ligand, adopt distorted square pyramidal

structures with an apical-O, cis-N ligand arrangement which allows maximum O-M

π-donation. The reactions of 23a or 24a with PMe₃yield the adducts [(MeBr₂Ox)₂M(CH₂-

Ph)(PMe₃)][B(C₆F₅)₄] (25a , M ) Zr; 26a , M ) Hf), which adopt trans-O, cis-N, cis-benzyl/

PMe₃structures analogous to those of the (Ox)₂MX₂complexes. The (MeBr₂Ox)₂M(η²-

CH₂Ph)⁺cations 23a and 24a exhibit moderate ethylene polymerization activity, while the

MeOx^-analogues 20a and 20b are inactive.

In tr od u ction

and σ-bond metathesis chemistry. We are interested

in exploring the chemistry of new d⁰metal alkyl

complexes which incorporate these properties but con-

tain non-cyclopentadienyl ancillary ligands to deter-

mine the extent to which the reactivity patterns ob-

served for Cp₂M(R)⁺species extend to other systems,

probing how ligand properties and metal geometries

influence reactivity, and developing new catalysts. A

Cationic group 4 metallocene alkyl complexes Cp₂MR⁺

(1, M ) Ti, Zr, Hf; Chart 1) have been studied exten-

sively because of their importance in olefin polymeri-

zation and other stoichiometric and catalytic pro-

cesses.^1,2These species are highly reactive because (i)

the cationic, d⁰, 14-electron metal center is very elec-

trophilic and can coordinate and activate/polarize a wide

variety of substrates,³(ii) the M-C bond is polarized

and the hydrocarbyl group is very nucleophilic, and (iii)

the bent-metallocene structure restricts coordination of

substrates/ligands to sites which are cis to the M-R

group. Together, these features lead to a rich insertion

(1) For olefin polymerization catalyzed by group 4 metallocene

complexes, see: (a) J ordan, R. F. Adv. Organomet. Chem. 1991, 32,

325. (b) Guram, A. S.; J ordan, R. F. In Comprehensive Organometallic

Chemistry, 2nd ed.; Lappert, M. F., Ed.; Pergamon: Oxford, 1995; Vol.

4, pp 589-625. (c) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger,

B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (d)

Bochmann, M. J . Chem. Soc., Dalton trans. 1996, 255. (e) Marks, T.

J . Acc. Chem. Res. 1992, 25, 57. (f) Horton, A. D. Trends Polym. Sci.

1994, 2, 158. (g) Mo¨hring, P. C.; Coville, N. J . J . Organomet. Chem.

1994, 479, 1.

^XAbstract published in Advance ACS Abstracts, J uly 1, 1997.

Group 4 Metal Alkyl Complexes

Organometallics, Vol. 16, No. 15, 1997 3283

and related carboranyl ligands,¹⁴and trimethylen-

emethanes.¹⁵Here, we describe the chemistry of new

group 4 metal alkyl complexes incorporating 8-quino-

linolato ligands 2 and 3 (Chart 1).

Ch a r t 1

Bis(8-quinolinolato) group 4 metal compounds of

general type (Ox)₂MX₂(4-6 in Chart 1; X ) Cl, OR,

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

1995, 14, 371. (b) Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.

J . Chem. Soc., Dalton trans. 1992, 367. (c) Corazza, F.; Solari, E.;

Floriani, C.; Chiesi-Villa, A.; Guastini, C. J . Chem. Soc., Dalton trans.

1990, 1335. (d) Mazzanti, M.; Rosset, J . M.; Floriani, C.; Chiesi-Villa,

A.; Guastini, C. J . Chem. Soc., Dalton trans. 1989, 953. (e) Floriani,

C. Polyhedron 1989, 8, 1717.

(7) (a) Cozzi, P. G.; Gallo, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli,

C. Organometallics 1995, 14, 4994. (b) Cozzi, P. G.; Floriani, C.; Chiesi-

Villa, A.; Rizzoli, C. Inorg. Chem. 1995, 34, 2921. (c) Cozzi, P. G.;

Floriani, C. J . Chem. Soc., Perkin trans. 1 1995, 2557.

(8) (a) Hughes, A. K.; Meetsma, A.; Teuben, J . H. Organometallics

1993, 12, 1936. (b) Canich, J . M. European Patent 420436, 1991. (c)

Canich, J . M.; Hlatky, G. G.; Turner, H. W. U.S. Patent 542236, 1990.

(d) Stevens, J . C.; Timmers, F. J .; Wilson, D. R.; Schmidt, G. F.; Nickias,

P. N.; Rosen, R. K.; Knight, G. W.; Lai, S. European Patent 416815,

1990. (e) Campbell, R. E., J r. U.S. Patent 5066741, 1991. (f) LaPointe,

R. E. European Patent 468651, 1991. (g) Devore, D. D.; Timmers, F.

J .; Hasha, D. L.; Rosen, R. K.; Marks, T. J .; Deck, P. A.; Stern, C. L.

Organometallics 1995, 14, 3132. (h) du Plooy, K. E.; Moll, U.; Wocadlo,

S.; Massa, W.; Okuda, J . Organometallics 1995, 14, 3129. For related

Sc complxes, see: (i) Shapiro, P. J .; Cotter, W. D.; Schaefer, W. P.;

Labinger, J . A.; Bercaw, J . E. J . Am. Chem. Soc. 1994, 116, 4623. (j)

Shapiro, P. J .; Bunnel, E.; Schaefer, W. P.; Bercaw, J . E. Organome-

tallics 1990, 9, 867. (k) Carpenetti, D. W.; Kloppenburg, L.; Kupec, J .

T.; Petersen, J . L. Organometallics 1996, 15, 1572. (l) Kloppenburg,

L.; Petersen, J . L. Organometallics 1996, 15, 7.

(9) (a) van der Linden, A.; Schaverien, C. J .; Meijboom, N.; Ganter,

C.; Orpen, A. G. J . Am. Chem. Soc. 1995, 117, 3008. (b) Scheverien, C.

J .; Van Der Linden, A. J . Polym. Prepr. (Am. Chem. Soc., Div. Polym.

Chem.) 1994, 35, 672. (c) Miyatake, T.; Mizunuma, K.; Seki, Y.;

Kakugo, M. Makromol. Chem., Rapid Commun. 1989, 10, 349. (d)

Kakugo, M; Miyatake, T.; Mizunuma, K.; Yagi, Y. U.S. Patent 5043,-

408. (e) Miyatake, T.; Mizunuma, K.; Kakugo, M. Makromol. Chem.,

Macromol Symp. 1993, 66, 203. (f) Reiger, B. J . Organomet. Chem.

1991, 420, C17. (g) Fandos, R.; Meetsma, A.; Teuben, J . H. Organo-

metallics 1991, 10, 59. (h) Fandos, R.; Teuben, J . H.; Helgesson, G.;

J agner, S. Organometallics 1991, 10, 1637.

(10) (a) Flores, J . C.; Chien, J . C. W.; Rausch, M. D. Organometallics

1995, 14, 1827. (b) Hagadorn, J . R.; Arnold, J . Organometallics 1994,

13, 4670. (c) Chernega, A. N.; Go´mez, R.; Green, M. L. H. J . Chem.

Soc., Chem. Commun. 1993, 1415. (d) Go´mez, R.; Duchateau, R.;

Chernega, A. N.; Teuben, J . H.; Edelmann, F. T.; Green, M. L. H. J .

Organomet. Chem. 1995, 491, 153. (e) Go´mez, R.; Duchateau, R.;

Chernega, A. N.; Meetsma, A.; Edelmann, F. T.; Teuben, J . H.; Green,

M. L. H. J . Chem. Soc., Dalton trans. 1995, 217. (f) Go´mez, R.; Green,

M. L. H.; Haggitt, J . L. J . Chem. Soc., Dalton trans. 1996, 939. (g)

Herskovics-Korine, D.; Eisen, M. S. J . Organomet. Chem. 1995, 503,

307. (h) Walther, D.; Fischer, R.; Go¨rls, H.; Koch, J .; Schweder, B. J .

Organomet. Chem. 1996, 508, 13. (i) Roesky, H. W.; Meller, B.;

Noltemeyer, M.; Schmidt, H.-G.; Scholz, U.; Scheldrick, G. M. Chem.

Ber. 1988, 121, 1403.

(11) Leading references, see: (a) Scollard, J . D.; McCoville, D. H.;

Vittal, J . J . Organometallics 1995, 14, 5478. (b) Cloke, F. G. N.;

Geldbach, T. J .; Hitchcock, P. B.; Love, J . B. J . Organomet. Chem. 1996,

506, 343. (c) Aoyagi, K.; Gantzel, P. K.; Kalai, K.; Tilley, T. D.

Organometallics 1996, 15, 923. (d) Herrmann, W. A.; Denk, M.; Albach,

R. W.; Behm, J .; Herdtweck, E. Chem. Ber. 1991, 124, 683. (e)

Herrmann, W. A.; Denk, M.; Scherer, W.; Klingan, F. R. J . Organomet.

Chem. 1993, 444, C21. (f) Warren, T. H.; Schrock, R. R.; Davis, W. M.

Organometallics 1996, 15, 562. (g) Minhas, R. K.; Scoles, L.; Wong, S.;

Gambarotta, S. Organometallics 1996, 15, 1113. (h) Horton, A. D.; de

With, J . J . Chem. Soc., Chem. Commun. 1996, 1375.

variety of non-Cp ancillary ligands have been explored

in this context in recent years, including, for example,

tetraazaannulenes, porphyrins, and other N₄-macro-

cycles,^4,5acen, salen, and other N₂O₂Schiff bases,⁶

bidentate N,O-ligands, such as hydroxyphenyloxazoli-

nato,⁷linked Cp-amido ligands, including Cp(CH₂)_nNR^2-

and CpSiR₂NR^2-,⁸alkoxides and chelating alkoxides,⁹

RNCRNR^-amidinate ligands,¹⁰amides and chelating

bisamides,¹¹boratabenzene,¹²borollides,¹³dicarbollide

(2) For other reactions involving group 4 metallocene complexes,

see: (a) Rodewald, S.; J ordan, R. F. J . Am. Chem. Soc. 1994, 116, 4491.

(b) Guram, A. S.; J ordan, R. F. J . Org. Chem. 1993, 58, 5595. (c) Guram,

A. S.; Guo, Z.; J ordan, R. F. J . Am. Chem. Soc. 1993, 115, 4902. (d)

Guram, A. S.; J ordan, R. F. J . Org. Chem. 1992, 57, 5994. (e) Guram,

A. S.; Swenson, D. C.; J ordan, R. F. J . Am. Chem. Soc. 1992, 114, 8991.

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

Guram, A. S.; J ordan, R. F.; Taylor, D. F. J . Am. Chem. Soc. 1991,

113, 1833. (h) J ordan, R. F.; Guram, A. S. Organometallics 1990, 9,

2116. (i) J ordan, R. F.; Taylor, D. F. J . Am. Chem. Soc. 1989, 111,

778. (j) Hong, Y.; Kuntz, B. A.; Collins, S. Organometallics 1993, 12,

964. (k) Hong, Y.; Norris, D.; Derek, J .; Collins, S. J . Org. Chem. 1993,

58, 3591. (l) Collins, S.; Ward, D. G. J . Am. Chem. Soc. 1992, 114,

5460. (m) Collins, S.; Koene, B. E.; Ramachandran, R.; Taylor, N. J .

Organometallics 1991, 10, 2092. (n) Tjaden, E. B.; Casty, G. L.; Stryker,

J . M. J . Am. Chem. Soc. 1993, 115, 9814. (o) Suzuki, K.; Maeta, H.;

Matsumoto, T. Tetrahedron Lett. 1989, 30, 4853. (p) Suzuki, K.; Maeta,

H.; Matsumoto, T.; Tsuchihashi, G. Tetrahedron Lett. 1988, 29, 3571.

(q) Maeta, H.; Suzuki, K. Tetrahedron Lett. 1992, 33, 5969. (r) Wipf,

P.; Xu, W. J . Org. Chem. 1993, 58, 825.

(3) (a) Wu, Z.; J ordan, R. F.; Petersen, J . L. J . Am. Chem. Soc. 1995,

117, 5867. (b) Guo, Z.; Swenson, D. C.; Guram, A. S.; J ordan, R. F.

Organometallics 1994, 13, 766. (c) Alelyunas, Y. W.; Guo, Z.; LaPointe,

R. E.; J ordan, R. F. Organometallics 1993, 12, 544. (d) J ordan, R. F.;

Bradley, P. K.; Baenziger, N. C.; LaPointe, R. E. J . Am. Chem. Soc.

1990, 112, 1289

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

Organometallics 1995, 14, 3539. (b) Uhrhammer, R.; Black, D. G.;

Gardner, T. G.; Olsen, J . D.; J ordan, R. F. J . Am. Chem. Soc. 1993,

115, 8493. (c) Giannini, L.; Solari, E.; De Angelis, S.; Ward, T, R.;

Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J . Am. Chem. Soc. 1995, 117,

5801 and references therein. (d) De Angelis, S.; Solari, E.; Gallo, E.;

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

(e) Floriani, C.; Ciurli, S.; Chiesi-Villa, A.; Guastini, C. Angew. Chem.,

Int. Ed. Engl. 1987, 26, 70. (f) Cotton, F. A.; Czuchajowska, J .

Polyhedron 1990, 9, 2553.

(12) Bazan, G. C.; Rodriguez, G.; Ashe, A. J ., III; Al-Ahmad, S.;

Mu¨ller, C. J . Am. Chem. Soc. 1996, 118, 2291.

(13) Quan, R. W.; Bazan, G. C.; Kiely, A. F.; Schaefer, W. P.; Bercaw,

J . E. J . Am. Chem. Soc. 1994, 116, 4489.

(14) (a) Crowther, D. J .; Swenson, D. C.; J ordan, R. F. J . Am. Chem.

Soc. 1995, 117, 10403. (b) Crowther, D. J .; Baenziger, N. C.; J ordan,

R. F. J . Am. Chem. Soc. 1991, 113, 1455. (c) Crowther, D. J .; J ordan,

R. F. Makromol. Chem., Macromol. Symp. 1993, 66, 121. (d) Kreuder,

C.; J ordan, R. F.; Zhang, H. Organometallics 1995, 14, 2993. (e) Bowen,

D. E.; J ordan, R. F.; Rogers, R. D. Organometallics 1995, 14, 3630. (f)

Siriwardane, U.; Zhang, H.; Hosmane, N. S. J . Am. Chem. Soc. 1990,

112, 9637. (g) Hosmane, N. S.; Wang, Y.; Zhang, H; Maguire, J . A.;

Waldho¨r, E.; Kaim, W.; Binder, H.; Kremer, R. K. Organometallics

1994, 13, 4156. (h) Thomas, C. J .; J ia, L.; Zhang, H.; Siriwardane, U.;

Maguire, J . A.; Wang, Y.; Brooks, K. A.; Weiss, V. P.; Hosmane, N. S.

Organometallics 1995, 14, 1365.

(5) (a) Brand, H.; Capriotti, J . A.; Arnold, J . Organometallics 1994,

13, 4469. (b) Brand H.; Arnold, J . Organometallics 1993, 12, 3655. (c)

Brand, H.; Arnold, J . J . Am. Chem. Soc. 1992, 114, 2266. (d) Shibata,

K.; Aida, T.; Inoue, S. Chem. Lett. 1992, 1173. (e) Shibata, K.; Aida,

T.; Inoue, S. Tetrahedron Lett. 1992, 33, 1077.

(15) Bazan, G. C.; Rodriguez, G.; Cleary, B. P. J . Am. Chem. Soc.

1994, 116, 2177.

3284 Organometallics, Vol. 16, No. 15, 1997

Bei et al.

Ch a r t 2

structure is favored. For the smaller later metals,

however, the M-O and M-N distances are more similar

and other isomers are observed. Additionally, electronic

factors, including the trans-influence and π-donor prop-

erties of the ligands, are likely to influence the struc-

tures of d⁰(Ox)₂MXX′ complexes.

Mass spectrometric results suggest that the d⁰(Ox)₂M

unit is very stable. The principal fragmentation pro-

cesses observed in the mass spectrum of (Ox)₂Ti(Cl)Cp

involve loss of Cl and/or Cp rather than disruption of

the (Ox)₂Ti core.^17aIn addition, Ox^-chelate ligands

have been widely used as complexation agents for the

quantitative analysis of transition metal ions.²²

On the basis of these observations, we hypothesized

that d⁰(Ox)₂M(R)⁺species of type 7 (Chart 1) should

be reasonably stable and should coordinate potential

substrates L cis to the M-R bond, yielding adducts 8.

Although it is difficult to predict whether the substrate

L will be sufficiently activated to react with the M-R

bond in 8, we reasoned that the reactivity of 8 could be

modified and ultimately tuned via appropriate substitu-

tion or elaboration of the Ox^-ligands. In this paper,

we describe the synthesis, properties, and ethylene

reactivity of zirconium and hafnium (Ox)₂MR₂and

(Ox)₂M(R)⁺complexes incorporating the 8-quinolinolato

ligands MeOx^-(2) and MeBr₂Ox^-(3) (Chart 1).

Cp; Ox^-) 8-quinolinolato) have been known for many

years.^16,17X-ray crystallographic studies established

that (Ox)₂TiCl₂(4) and (Ox)₂Ti{O-2,6-(ⁱPr)₂C₆H₃}₂(5)

adopt distorted octahedral structures with a trans-O,

cis-N, cis-X ligand arrangement (Chart 1).¹⁸NMR

studies of 5 showed that this C₂-symmetric structure is

retained in solution, but that inversion of the metal

configuration (i.e., Λ/∆ interconversion, racemization)

is rapid on the NMR time scale at elevated tempera-

tures.¹⁹Analogous structures have been observed for

(Ox)₂MCl(η⁵-Cp) (6; M ) Ti, Zr) and high oxidation state

(d⁰) group 5 and group 6 complexes, such as (Ox)₂V-

(dO)(OsⁱPr) and (Ox)₂Mo(dO)₂. However, other iso-

mers have been observed for later transition metal (dⁿ,

n * 0) (Ox)₂MXX′ complexes.²⁰For example, (MeOx)₂-

Ru(NO)Cl exists as two isomers; the MeOx^-ligands

adopt a cis-O, trans-N arrangement in one isomer and

a cis-O, cis-N arrangement in the other.^20a-dThe

MeOx^-donor groups have a cis-O, cis-N arrangement

in (MeOx)₂Tc(dO)Cl^20eand a cis-O, trans-N arrange-

ment in (MeOx)₂Co(en)⁺.^20f

Resu lts a n d Discu ssion

These structural trends may be rationalized in terms

of simple valence shell electron pair repulsion concepts

as developed in detail by Kepert.²¹Analysis of donor

atom-donor atom repulsions in (bidentate)₂MX₂com-

plexes (X ) unidentate ligand, Chart 2) reveals that (i)

the cis-X structures are preferred in general and (ii)

donor atom-donor atom repulsions at site B are less

than at site A, so that site B will be occupied by that

end of an unsymmetrical bidentate ligand which forms

the shortest bond to the metal. The M-O distances are

significantly shorter than the M-N distances in early

metal (Ox)₂MX₂species, so the trans-O, cis-N, cis-X

Syn t h esis of (MeOx)₂MR ₂a n d (MeBr ₂Ox)₂MR ₂

Com p lexes (M ) Zr , Hf) via Alk a n e Elim in a tion .

Slow addition of 2 equiv of 2-Me-8-quinolinol (MeOxH,

2-H) to ZrR₄(R ) CH₂Ph, CH₂CMe₃, CH₂SiMe₃) in

toluene or benzene results in the formation of (MeOx)₂-

ZrR₂complexes 9a -c in high yield (eq 1). Complexes

(16) The unsubstituted 8-quinolinolato ligand is also referred to as

“oxinato” or “ox”, and the methyl derivative 2-Me-8-quinolinolato (2)

is referred to as “quinaldinate”, “8-hydroxyquinaldinate”, or “quin” in

the literature. In this paper, “Ox” is used as a general abbreviation

for substituted 8-quinolinolato ligands.

(17) (a) Charalambous, J .; Frazer, M. J .; Newton, W. E. J . Chem.

Soc. A. 1971, 15, 2487. (b) Frazer, M. J .; Rimmer, B. J . Chem. Soc. A

1968, 69. (c) Frazer, M. J .; Rimmer, B. J . Chem. Soc. A. 1968, 2273.

(d) Harrod, J . F.; Taylor, K. R. Inorg. Chem. 1975, 14, 1541.

(18) For X-ray structural studies of early transition metal d⁰(Ox)₂-

MX₂or (Ox)₂MXX′ complexes, see: (a) Studd, B. F.; Swallow, A. G. J .

Chem. Soc. A. 1968, 1961. (b) Swallow, A. G.; Studd, B. F. J . Chem.

Soc., Chem. Commun. 1967, 1197. (c) Bird, P. H.; Fraser, A. R.; Lau,

C. F. Inorg. Chem. 1973, 12, 1322. (d) Matthews, J . D.; Singer, N.;

Swallow, A. G. J . Chem. Soc. A. 1970, 2545. (e) Wang, J .; Li, J .; Gong,

Y. Chem. Res. Chin. Univ. 1992, 8, 212. (f) J eannin, Y.; Launay, J . P.;

Seid Sedjadi, M. A. J . Coord. Chem. 1981, 11, 27. (g) Scheidt, W. R.

Inorg. Chem. 1973, 12, 1758. (h) Atovmyan, L. O.; Sokolava, Yu. A. J .

Chem. Soc., Chem. Commun. 1969, 649. (i) Yamada, S.; Katayama,

C.; Tanaka, J .; Tanaka, M. Inorg. Chem. 1984, 23, 253.

(19) (a) Bickley, D. G.; Serpone, N. Inorg. Chem. 1979, 18, 2200. (b)

Harrod, J . F.; Taylor, K. J . Chem. Soc., Chem. Commun. 1971, 696.

(20) Later transition metal (dⁿ, n * 0) complexes, see: (a) Kamata,

Y.; Kimura, J .; Hirota, R.; Miki, E.; Mizumachi, K.; Ishimori, T. Bull.

Chem. Soc. J pn. 1987, 60, 1343. (b) Kamata, Y.; Miki, E.; Hirota, R.;

Mizumachi, K.; Ishimori, T. Bull. Chem. Soc. J pn. 1988, 61, 594. (c)

Kamata, H.; Konish, Y.; Kamata, Y.; Miki, E.; Mizumachi, K.; Ishimori,

T.; Nagai, T.; Tanaka, M. Chem. Lett. 1988, 1, 159. (d). Miki, E.;

Masano, H.; Iwasaki, H.; Tomizawa, H.; Mizumachi, K.; Ishori, T.

Inorg. Chim. Acta 1993, 205, 129. (e) Wilcox, B.; Heeg, M. J .; Deutsch,

E. Inorg. Chem. 1984, 23, 2962. (f) Yamamoto, Y.; Toyota, E. Bull.

Chem. Soc. J pn. 1984, 57, 47.

9a (orange) and 9b (yellow) were obtained as pure solids

by recrystallization from toluene or toluene/pentane.

However, 9c could not be recrystallized efficiently due

to its high solubility in these solvents. The hafnium

dibenzyl complex (MeOx)₂Hf(CH₂Ph)₂(10a ) was gener-

ated by the analogous reaction of 2-H with Hf(CH₂Ph)₄.

In initial experiments, it was found that slow addition

of 2 equiv of the more acidic quinolinol MeBr₂OxH (3-

H) to Zr(CH₂Ph)₄in toluene results in an exothermic

reaction and formation of (MeBr₂Ox)₂Zr(CH₂Ph)₂(11a )

contaminated with significant amounts of (MeBr₂Ox)₃Zr-

(CH₂Ph) (12), (MeBr₂Ox)₄Zr (13), and unreacted Zr(CH₂-

(22) Leading references, see: (a) Phillips, J . P. Chem. Rev. 1956,

56, 271. (b) Stary, J . The Solvent Extraction of Metal Chelates;

Pergamon: Oxford, 1964; p 80. (c) Yatirajam, V.; Arya, S. P. Talanta

1976, 23, 596. (d) Uhlemann, E.; Opitz, B.; Schilde, U. Z. Anorg. Allg.

Chem. 1985, 520, 167. (e) Isshiki, K.; Tsuji, F.; Kuwamoto, T. Anal.

Chem. 1987, 59, 2491.

(21) Kepert, D. L. In Progress in Inorganic Chemistry; Lippard, S.

L., Ed.; J ohn Wiley & Sons: New York, 1977; Vol. 23, Chapter 1.

Group 4 Metal Alkyl Complexes

Organometallics, Vol. 16, No. 15, 1997 3285

Ph)₄(eq 2).^23,24The identities of these compounds were

compounds are insoluble in benzene and toluene and

only slightly soluble in methylene chloride and are, thus,

difficult to isolate. However, 15 and 16 may be gener-

ated in situ and used in subsequent reactions without

separation from LiCl.²⁵The identities of 15 and 16 were

confirmed by alternate synthesis from [HNMe₃]Cl and

9a and 11a (eq 5).

confirmed by independent synthesis from Zr(CH₂Ph)₄

and 3 or 4 equiv of MeBr₂OxH. It was subsequently

determined that 11a can be prepared free of these side

products by performing the reaction at higher dilution

(eq 3). The hafnium analogue 14a was prepared in a

The derivatization of 16 has been extensively inves-

tigated, as summarized in Scheme 1. The reaction of

16 and 2 equiv of PhCH₂MgCl in toluene affords (MeBr₂-

Ox)₂Zr(CH₂Ph)₂(11a ) in good yield. Similarly, the

reaction of 16 with 2 equiv of LiNMe₂in Et₂O or toluene

yields bis(amide) 17 cleanly.²⁶

In contrast, attempts to prepare (MeBr₂Ox)₂ZrMe₂by

methylation of 16 were unsuccessful. The reaction of

16 and MeLi, MeMgI, or Me₂Mg gave insoluble black

products, even under low-temperature conditions in

toluene or toluene/ether solution (-78 to -40 °C). There

is no reaction between ZnMe₂and 16 in toluene at

ambient temperature. The reaction of 16 and AlMe₃

yields the MeBr₂Ox^-transfer product (MeBr₂Ox)AlMe₂

(18), which was prepared independently by the reaction

of MeBr₂OxH and AlMe₃. The parent compound (Ox)-

AlMe₂was prepared previously and shown to be mon-

omeric.²⁷Attempts to prepare (MeBr₂Ox)₂ZrMe₂from

other Zr(IV) precursors were also unsuccessful. The

reaction of (MeBr₂Ox)₄Zr (13) with 2 equiv of AlMe₃

yields 18 and a black insoluble material, and the

reaction of 17 with either 2 or 4 equiv of AlMe₃yields

18 and other unidentified species.²⁸These results

suggest that (MeBr₂Ox)₂ZrMe₂may be thermally un-

stable (vide infra).

similar manner (eq 3). Complexes 11a and 14a were

obtained as analytically pure orange solids by crystal-

lization from toluene. Neopentyl complex 11b was

generated by the reaction of 2 equiv of MeBr₂OxH (3-

H) and Zr(CH₂CMe₃)₄in hexanes.

Syn t h esis a n d R ea ct ivit y of (MeOx)₂Zr Cl₂a n d

(MeBr ₂Ox)₂Zr Cl₂. The dichloride complexes (MeOx)₂-

ZrCl₂(15) and (MeBr₂Ox)₂ZrCl₂(16) are of interest as

potential precursors to other (MeOx)₂ZrR₂and (MeBr₂-

Ox)₂ZrR₂species. The reaction of ZrCl₄with 2 equiv of

MeOxLi (2-Li) or MeBr₂OxLi (3-Li) in ether generates

15 or 16 in high yield (eq 4) as yellow solids. These

The reactivity of 15 was only briefly investigated.

Alkylation of 15 with 2 equiv of LiCH₂CMe₃in C₆D₆

(24) (Ox)₄Zr has been characterized by X-ray diffraction. Lewis, D.

F.; Fay, R. C. J . Chem. Soc., Chem. Commun. 1974, 1046.

(25) The reaction of ZrCl₄with 3-Na in methylene chloride generates

(MeBr₂Ox)₄Zr.

(26) Attempts to prepare (MeBr₂Ox)₂Zr(NMe₂)₂by reaction of 2 equiv

of 3-H and Zr(NMe₂)₄under a variety of conditions yielded mixtures

of (MeBr₂Ox)_nZr(NMe₂)_4-n(n ) 0 - 4).

(27) (a) Sen, B.; White, G. L. J . Inorg. Nucl. Chem. 1973, 35, 497.

(b) Sen, B.; White, G. L.; Wander, J . D. J . Chem. Soc., Dalton trans.

1972, 447. (c) For related compounds, see: van Vliet, M. R. P.; van

Koten, G.; de Keijser, M. S.; Vrieze, K. Organometallics 1987, 6, 1652.

(28) For the use of AlMe₃as a methylation reagent for L_nM(NMe₂)₂

compounds, see: (a) Kim, I.; J ordan, R. F. Macromolecules 1996, 29,

489. (b) Diamond, G. D.; J ordan, R. F.; Petersen, J . L. J . Am. Chem.

Soc. 1996, 118, 8024.

(23) For comparison, the pK_aof phenol and 2,4-bromophenol are 9.9

and ca. 7.7 (estimated from the values of 2,3-chlorophenol, 2,3-

bromophenol, and 2,4-chlorophenol), respectively. Dean, J . A. Hand-

book of Organic Chemistry; McGraw-Hill: New York, 1987; Table 8-1.

3286 Organometallics, Vol. 16, No. 15, 1997

Bei et al.

Ta ble 1. Selected Bon d Dista n ces (Å) a n d Bon d

An gles (d eg) for (MeOx)₂Zr (CH₂P h )₂(9a )

Zr-C(201)

Zr-C(202)

Zr-C(301)

Zr-C(302)

2.286(4)

2.69

2.293(4)

3.20

Zr-N(1)

2.450(3)

2.444(3)

2.051(2)

2.052(2)

Zr-N(101)

Zr-O(3)

Zr-O(103)

C(201)-Zr-C(301)

C(201)-Zr-N(1)

C(201)-Zr-O(3)

91.0(2)

117.7(2)

96.9(1)

N(1)-Zr-N(101)

N(101)-Zr-O(3)

N(101)-Zr-O(103)

O(3)-Zr-O(103)

Zr-C(201)-C(202)

81.2(1)

107.15(9)

70.45(9)

170.5(1)

89.4(2)

C(201)-Zr-N(101) 153.6(1)

C(301)-Zr-N(101)

C(301)-Zr-O(3)

C(301)-Zr-N(1)

N(1)-Zr-O(3)

80.4(1)

86.0(1)

144.3(1)

Zr-C(301)-C(302) 115.1(2)

Zr-O(3)-C(3) 125.7(2)

70.70(9) Zr-O(103)-C(103) 125.9(2)

99.8(1)

N(1)-Zr-O(103)

compounds,^29,30and the Zr-N bonds of 9a (Zr-N(1),

2.450(3) Å; Zr-N(101), 2.444(3) Å) are within the range

observed for other Zr(IV) pyridine complexes (2.38-2.47

Å).^29c,31The Zr coordination geometry in 9a is, thus,

similar to that in other early metal (Ox)₂MX₂com-

plexes,^17,18and the Zr-O and Zr-N bonding is quite

normal.

F igu r e 1. Molecular structure of (MeOx)₂Zr(CH₂Ph)₂(9a ).

Sch em e 1

While the C(301)-C(307) benzyl ligand shows normal

η¹-bonding to Zr in this complex (Zr-C(301)-C(302),

115.1(2)°; Zr-C(302), 3.20Å), the C(201)-C(207) benzyl

ligand is distorted such that the Zr-C(201)-C(202)

angle is acute (89.4(2)°) and the Zr-C_ipsocarbon (Zr-

C(202), 2.69 Å) is short. This η²-benzyl bonding mode

results from a weak Zr‚‚‚Ph π interaction and is

characteristic of electron-deficient early transition metal

benzyl complexes.^8a,32Complex 9a is formally a 16-

electron species, counting the MeOx^-oxygens as 4-elec-

tron (σ, π) donors and neglecting the Zr‚‚‚Ph interaction.

The Ph ring of the distorted benzyl ligand points toward

a MeOx^-pyridine ring and away from the normal

benzyl ligand.

Electr on ic Str u ctu r e of (MeOx)₂MR₂Com p lexes.

An extended Hu¨ckel molecular orbital (EHMO) analysis

of the model species (MeOx)₂ZrMe₂(with the same

geometry as observed for 9a ) illustrates several impor-

tant features of the bonding in these systems and also

provides insight to the origin of the η²-benzyl interac-

tion.³³As schematically illustrated in Figure 2, the two

affords 9b cleanly; however, attempted methylation of

15 with Me₂Mg yields a mixture of unidentified products

(eq 6).

(29) (a) Zambrano, C. H.; Profilet, R. D.; Hill, J . E.; Fanwick, P. E.;

Rothwell, I. P. Polyhedron 1993, 12, 689. (b) Kresinski, R. A.; Isam,

L.; Hamor, T. A.; J ones, C. J .; McCleverty, J . A. J . Chem. Soc., Dalton

trans. 1991, 1835. (c) Zambrano, C. H.; McMullen, A. K.; Kobriger, L.

M.; Fanwick, P. E.; Rothwell, I. P. J . Am. Chem. Soc. 1990, 112, 6565.

(d) Profilet, R. D.; Zambrano, C. H.; Fanwick, P. E.; Nash, J . J .;

Rothwell, I. P. Inorg. Chem. 1990, 29, 4362. (e) Fanwick, P. E.;

Kobriger, L. M.; McMullen, A. K.; Rothwell, I. P. J . Am. Chem. Soc.

1986, 108, 8095. (f) Chamberlain, L. R.; Durfee, L. D.; Fanwick, P. E.;

Kobriger, L. M.; Latesky, S. L.; McMullen, A. K.; Steffey, B. D.;

Rothwell, I. P.; Folting, K.; Huffman, J . C. J . Am. Chem. Soc. 1987,

109, 6068. (g) Latesky, S. L.; McMullen, A. K.; Niccolai, G. P.; Rothwell,

I. P.; Huffman, J . C. Organometallics 1985, 4, 1896. (h) Erker, G.; Dorf,

U.; Lecht, R.; Ashby, M. T.; Aulbach, M.; Schlund, R.; Kruger, C.;

Mynott, R. Organometallics 1989, 8, 2037. (i) McMullen, A. K.;

Rothwell, I. P.; Huffman, J . C. J . Am. Chem. Soc. 1985, 107, 1072.

(30) For discussions of M-OR bonding in early metal complexes,

see: Howard, W. A.; Trnka, T. M.; Parkin, G. Inorg. Chem. 1995, 34,

5900 and references therein.

(31) (a) Howard, W. A.; Parkin, G. J . Am. Chem. Soc. 1994, 116,

606. (b) Williams, D. N.; Piarulli, U.; Floriani, C.; Chiesi-Villa, A.;

Rizzoli, C. J . Chem. Soc., Dalton trans. 1994, 1243. (c) Walsh, P. J .;

Hollander, F. J .; Bergman, R. G. J . Am. Chem. Soc. 1990, 112, 894.

(d) Walsh, P. J .; Carney, M. J .; Bergman, R. G. J . Am. Chem. Soc.

1991, 113, 6343. (e) Carney, M. J .; Walsh, P. J .; Hollander, F. J .;

Bergman, R. G. Organometallics 1992, 11, 761. (f) Hoffman, D. M.;

Lee, S. Inorg. Chem. 1992, 31, 2675. (g) Arnold, J .; Woo, H.-G.; Tilley,

T. D. Organometallics 1988, 7, 2045. (h) Moore, E. J .; Straus, D. A.;

Armantrout, J .; Santarsiero, B. D.; Grubbs, R. H.; Bercaw, J . E. J .

Am. Chem. Soc. 1983, 105, 2068. (i) Peterson, E. J .; Von Dreele, R. B.;

Brown, T. M. Inorg. Chem. 1976, 15, 309.

X-r a y Str u ctu r a l An a lysis of (MeOx)₂Zr (CH₂P h )₂

(9a ). The molecular structure of (MeOx)₂Zr(CH₂Ph)₂

(9a ) was determined by X-ray crystallography and is

illustrated in Figure 1. Selected bond distances and

angles are given in Table 1. Complex 9a adopts a

distorted octahedral structure analogous to those of 4-6

with a trans-O, cis-N, cis-benzyl ligand arrangement.

The O-Zr-O bond angle (170.5(1)°) approaches the

ideal O_hvalue. The intrachelate O-Zr-N angles are

acute (O(3)-Zr-N(1), 70.70(9)°; O(103)-Zr-N(101),

70.45(9)°) due to the small MeOx^-bite angle, and as a

result, the remaining trans angles are significantly

reduced from ideal O_hvalues (N(101)-Zr-C(201), 153.6-

(1)°; N(1)-Zr-C(301), 144.3(1)°). The Zr-O-C units

are bent (Zr-O(3)-C(3), 125.7(2)°; Zr-O(103)-C(103),

125.9(2)°), indicating that the MeOx^-oxygens are sp²-

hybridized. The Zr-O distances (Zr-O(3), 2.051(2) Å,

Zr-O(103), 2.052(2)Å) are typical for Zr(IV) phenoxide

Group 4 Metal Alkyl Complexes

Organometallics, Vol. 16, No. 15, 1997 3287

F igu r e 3. (a) Key frontier orbitals of the benzyl anion

involved in M-(η²-CH₂Ph) interactions. (b) Schematic

illustration of the Zr‚‚‚Ph interaction in 9a , involving

overlap of the benzyl Ψ_πand Zr d_xzorbitals.

closely spaced unoccupied frontier orbitals is sensitive

to the computational method and parameters, it is clear

that these orbitals have both metal d and ligand π*

character.

The key frontier orbitals of the benzyl anion which

are localized on the methylene and ipso carbons and

which interact strongly with the metal acceptor orbitals

in an η²-benzyl complex, are Ψ_CHand Ψ_π(Figure 3),

2

which are combinations of the methylene p lone pair

orbital and the phenyl HOMO (highest occupied molec-

ular orbital).^32c,35The M-(η²-benzyl) bond may be

considered to comprise a M-CH₂Ph σ bond formed by

F igu r e 2. Schematic illustration of the frontier orbitals

of the model compound (MeOx)₂ZrMe₂, derived from 9a by

replacement of the benzyl groups with methyl groups, as

determined by an EHMO analysis.

overlap of Ψ_CHand a suitable metal σ-acceptor orbital

2

and a Ph‚‚‚M interaction resulting from overlap of Ψ_π

with an empty metal d orbital. As illustrated in Figure

3b, a (MeOx)₂Zr(η²-CH₂Ph)(R) species (e.g., 9a ) is ex-

pected to adopt a conformation in which the η²-benzyl

phenyl group lies over a M-N bond, since this orienta-

tion maximizes overlap of the Ψ_πorbital and the metal

d_xzacceptor orbital. This is the structure observed for

9a in the solid state.

highest occupied orbitals of (MeOx)₂ZrMe₂are the

MeOx^-oxygen lone pair orbitals admixed with MeOx^-

C-C bonding orbitals. The two lowest unoccupied

orbitals are MeOx^--based π* antibonding orbitals which

are primarily localized on the N, C2, and C4 (see Chart

1 for numbering). These orbitals correspond to the 3b₁

π* orbital of pyridine³⁴and also contain ca. 15% LUMO

(lowest unoccupied molecular orbital) and 8% LUMO

+ 1 metal d character (not shown). The d_xzorbital lies

at slightly higher energy, followed by d_xyand d_yz

combinations, which are destabilized by π-donation from

the MeOx^-oxygens. While the precise ordering of the

NMR Ch a r a cter iza tion of (MeOx)₂MR₂a n d (Me-

1

Br ₂Ox)₂MR₂Com p lexes. The room-temperature H

NMR spectra of 9a -c, 11a ,b, and 14a each contain a

single set of MeOx^-or MeBr₂Ox^-resonances, a single

set of Ph (9a , 11a , 14a ), CMe₃(9b, 11b), or SiMe₃(9c)

resonances, and an AB pattern for the MCH₂hydrogens.

These spectra are consistent with the C₂-symmetric

trans-O, cis-N, cis-R structures shown in eqs 1-5, in

which the MCH₂R hydrogens are diastereotopic due to

their proximity to the chiral metal center.

(32) (a) Pellecchia, C.; Immirzi, A.; Pappalardo, D.; Peluso, A.

Organometallics 1994, 13, 3773. (b) Bochmann, M.; Lancaster, S. J .

Organometallics 1993, 12, 633. (c) Dryden, N. H.; Legzdins, P.; Trotter,

J .; Yee, V. C. Organometallics 1991, 10, 2857. (d) Alelyunas, Y. W.;

J ordan, R. F.; Echols, S. F.; Borkowsky, S. L.; Bradley, P. K. Organo-

metallics 1991, 10, 1406. (e) J ordan, R. F.; LaPointe, R. E.; Baenziger,

N.; Hinch, G. D. Organometallics 1990, 9, 1539. (f) Scholz, J .; Schlegel,

M.; Thiele, K. H. Chem. Ber. 1987, 120, 1369. (g) J ordan, R. F.;

LaPointe, R. E.; Bajgur, C. S.; Echols, S. F.; Willett, R. J . Am. Chem.

Soc. 1987, 109, 4111. (h) Latesky, S. L.; McMullen, A. K.; Niccolai, G.

P.; Rothwell, I. P. Organometallics 1985, 4, 902. (i) Edwards, P. G.;

Andersen, R. A.; Zalkin, A. Organometallics 1984, 3, 293. (j) Girolami,

G. S.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse, M. B. J . Chem.

Soc., Dalton Trans. 1984, 2789. (k) Mintz, E. A.; Moloy, K. G.; Marks,

T. J .; Day, V. W. J . Am. Chem. Soc. 1982, 104, 4692. (l) Davies, G. R.;

J arvis, J . A. J .; Kilbourn, B. T. J . Chem. Soc., Chem. Commun. 1971,

1511. (m) Davies, G. R.; J arvis, J . A. J .; Kilbourn, B. T.; Pioli, A. J . P.

J . Chem. Soc., Chem. Commun. 1971, 677. (n) Coles, M. P.; Dalby, C.

I.; Gibson, V. C.; Clegg, W.; Elsegood, M. R. J . J . Chem. Soc., Chem.

Commun. 1995, 1709.

The room-temperature ¹H NMR spectrum of 10a

contains a single set of MeOx^-and Ph resonances and

a sharp singlet rather than an AB pattern for the HfCH₂

hydrogens. However, as the temperature is lowered, the

HfCH₂singlet splits to a sharp AB pattern without

intermediate broadening. The lack of broadening indi-

cates that these line shape changes result from a change

in the ∆υ/J ratio with temperature rather than a

chemical exchange process (vide infra), and therefore,

10a most likely has the same solution structure as the

other (MeOx)₂MR₂and (MeBr₂Ox)₂MR₂complexes.

The presence of one distorted and one normal benzyl

ligand in the solid state structure of 9a suggests that

η²-benzyl interactions may also be present in (Ox)₂M(CH₂-

Ph)₂species in solution. Distorted M-CH₂-Ph groups

(33) The Extended Hu¨ckel calculations were performed on a CAChe

system (release 3.6) using the standard parameter set provided with

this system (K ) 1.75). Very similar results were obtained using the

Alverez parameters provided with this software, the principal differ-

ence being inversion of the ordering of the closely-spaced metal-based

and ligand-based LUMOs.

(35) (a) Dorigo, A. E.; Li, Y.; Houk, K. N. J . Am. Chem. Soc. 1989,

111, 6942. (b) Fleming, I. Frontier Orbitals and Chemical Reactions;

Wiley: New York, 1976; p 55.

(34) J orgensen, W. L.; Salem, L. The Organic Chemist’s Book of

Orbitals; Academic: New York, 1973; p 263.

3288 Organometallics, Vol. 16, No. 15, 1997

Bei et al.

1

can be detected by H and ¹³C NMR spectroscopy; in

Ti{O-2,6-(ⁱPr)₂C₆H₃}₂(∆G^q(racemization) ) 17.0(3) kcal/

mol) and proposed that racemization proceeds via Ti-N

bond cleavage and formation of a configurationally labile

five-coordinate intermediate.¹⁹Ti-N bond dissociation

is promoted by the ortho-methyl substituent in (MeOx)₂-

Ti{O-2,6-(ⁱPr)₂C₆H₃}₂, resulting in the lower barrier

observed in this case. Similar processes are possible for

(Ox)₂ZrR₂and (Ox)₂HfR₂complexes. As noted above,

particular, the reduction of the M-C-C angle and

concomitant increase in H-C-H angle which results

from the M‚‚‚Ph interaction are manifested by reduced

J _HH(<ca. 10 Hz) and large J _CHvalues (>ca. 125 Hz)

for the MCH₂Ph group.^32,36For example, the J _HHvalues

for (EBTHI)Zr(η¹-CH₂Ph)₂(EBTHI ) ethylenebis(tet-

rahydroindenyl)) and (EBTHI)Zr(η²-CH₂Ph)(CH₃CN)⁺

are 11.2 and 7.1 Hz, respectively, and the J _CHvalues

for Cp₂Zr(η¹-CH₂Ph)₂and Cp₂Zr(η²-CH₂Ph)(CH₃CN)⁺

are 119 and 145 Hz, respectively.^32e,gZirconium benzyl

complexes 9a and 11a exhibit J _CH(CH₂) values (9a , 129

Hz; 11a , 130 Hz) and J _HHvalues (9a , 8.5 Hz; 11a , 8.8

Hz) which are intermediate between the values for the

η²-benzyl and normal benzyl ligands in the metallocene

systems listed above, suggesting that the benzyl ligands

in these compounds have some η²character in solution.

The ¹H NMR spectra of 9a and 11a do not change

significantly when the sample temperature is lowered

to -85 °C; the ortho- and meta-Ph resonances broaden,

but the ZrCH₂AB pattern and the Ox^-resonances do

not change. It is likely that the static structures of 9a

and 11a contain one η¹-benzyl and one η²-benzyl ligand,

which exchange rapidly on the NMR time scale. The

HfCH₂J _CHand J _HHvalues for hafnium benzyl com-

plexes 10a (120, 10.2 Hz; -55 °C) and 14a (122, 10.9

Hz) are in the range observed for normal benzyl

complexes, indicating that these complexes have sig-

nificantly less η²-benzyl character than Zr analogues 9a

and 11a and probably have η¹structures.

1

the H NMR spectra of 9a -c, 11a , and 14a all exhibit

AB patterns for the MCH₂hydrogens at room temper-

ature, which implies that racemization is slow on the

NMR time scale under these conditions. To probe this

issue, high-temperature spectra of 9b, 11b, and 14a

were investigated. In all three cases, the MCH₂AB

patterns broaden and coalesce to singlets as the tem-

perature is raised, indicating that racemization is rapid

on the NMR time scale at higher temperatures. Race-

mization barriers determined from these line shape

changes are as follows: ∆G^q(racemization) 9b, 15.1(1)

kcal/mol; 11b, 15.7(1) kcal/mol; 14a , 17.5(1) kcal/mol.^39,40

Thus, the racemization barriers are insensitive to the

presence of the electron-withdrawing Br substituents

on the Ox^-ligands (9b vs 11b). This racemization

process probably proceeds by a dissociation mechanism

(eq 7).

The J _CH(ZrCH₂) values for 9b (105 Hz) and 9c (103

Hz) are low, as typically observed in d⁰metal complexes

containing CH₂CMe₃and CH₂SiMe₃ligands.³⁷The low

J _{C -H}values may result from R-agostic interactions or

R

Th er m a l Rea r r a n gem en t of (MeOx)₂Zr (CH₂P h )₂.

Thermolysis of 11a results in migration of a benzyl

group from Zr to C2′ of one of the MeBr₂Ox^-ligands,

yielding rearrangement product 19 as a single diaste-

reomer (eq 8). This reaction is 75% complete after 1.5

h at 70 °C (toluene-d₈); however, 19 is further converted

to unidentified products after more prolonged thermoly-

sis or at higher temperatures. Complex 19 was isolated

as a yellow solid.

simply from steric interactions associated with the bulky

CMe₃or SiMe₃groups, which increase the Zr-C-

(C,Si) angle, leading to a small H-C-H angle and

concomitantly small J _CHvalues.

Dyn a m ic NMR Beh a vior of (Ox)₂MR ₂Com -

p lexes. It is well-documented that six-coordinate, bis-

(chelate) (AA)₂MXX′ and (AB)₂MXX′ complexes can

undergo inversion of configuration at the metal (i.e.,

interconversion of ∆ and Λ stereoisomers) by twist or

bond-rupture mechanisms.^19,38Serpone determined the

racemization barriers for (Ox)₂Ti{O-2,6-(ⁱPr)₂C₆H₃}₂

(∆G^q(racemization) ) 20.0(3) kcal/mol) and (MeOx)₂-

The ¹H NMR spectrum of 19 was completely assigned

using COSY and NOESY data and general chemical

shift trends and shows that this compound has C₁

symmetry. The H3 (δ 7.15), H4 (δ 8.37), and Me (δ 2.07)

resonances for one chelate ligand (the unprimed MeBr₂O

in eq 8) appear in the normal ranges for (MeBr₂Ox)₂Zr

complexes (e.g., 11a ). However, the resonances for the

other N,O-ligand (the primed MeBr₂O in eq 8) are

unusual. The H3′ (δ 4.99) and H4′ (δ 6.74) resonances

are shifted upfield into the aromatic olefin region (cf.

styrene H1 δ 7.0; H2 δ 5.05, 5.35), and the J _H3′-H4′value

(9.5 Hz) is larger than the normal J _H3-H4values

observed for (MeBr₂Ox)₂Zr complexes (ca. 8.6 Hz). The

(36) Additionally, for many η²-benzyl complexes, the o-Ph ¹H NMR

resonances and the CH₂and C_ipso¹³C NMR resonances appear at high

field. However, for (Ox)₂MR₂complexes, the ¹H NMR shifts of the o-Ph

hydrogens may also be influenced by the ring currents of the Ox^-

ligands and it is difficult to distinguish the benzyl C_ipsoresonance from

the other C_ipsoresonances in the ¹³C NMR spectrum. Therefore, these

criteria are less useful probes of the benzyl bonding mode in (Ox)₂M-

(CH₂Ph)X species.

(37) See discussions in the following: (a) Guo, Z.; Swenson, D. C.;

J ordan, R. F. Organometallics 1994, 13, 1424. (b) Poole, A. D.; Williams,

D. N.; Kenwright, A. M.; Gibson, V. C.; Clegg, W.; Hockless, D. C. R.;

O’Neil, P. A. Organometallics 1993, 12, 2549. (c) Bruno, J . W.; Smith,

G. M.; Marks, T. J .; Fair, C. K.; Schultz, A. J .; Williams, J . M. J . Am.

Chem. Soc. 1986, 108, 40. (d) Amorose, D. M.; Lee, R. A.; Petersen, J .

L. Organometallics 1991, 10, 2191.

(38) (a) Denekamp, C. I. F.; Evans, D. F.; Slawin, A. M. Z.; Williams,

D. J .; Wong, C. Y.; Woollins, J . D. J . Chem. Soc., Dalton. trans. 1992,

2375. (b) Gau, H.; Fay, R. C. Inorg. Chem. 1990, 29, 4974. (c) Nieto, J .

L.; Galindo, F.; Gutie´rrez, A. M. Polyhedron 1985, 4, 1611. (d) Willem,

R.; Gielen, M.; Pepermans, H.; Brocas, J .; Fastenakel, D.; Finocchiaro,

P. J . Am. Chem. Soc. 1985, 107, 1146. (e) Willem, R.; Gielen, M.;

Pepermans, H.; Hallenga, K.; Recca, A.; Finocchiaro, P. J . Am. Chem.

Soc. 1985, 107, 1153. (f) Holm, R. H. In Dynamic Nuclear Magnetic

Resonance Spectroscopy; J ackman, L. M., Cotton, F. A., Eds.; Academic

Press: New York, 1975; Chapter 9.

(39) (a) Racemization barriers ∆G^q(racemization) were determined

from the coalesence of the MCH₂AB patterns using the following

equations: ∆G^q(racemization) ) 4.576T_c[10.319 + log(T_c/k_c)], where

T_cis the coalesence temperature and k_cis the exchange rate constant

at coalesence, which is given by k_c) π[(∆υAB²+6J _AB

]

^1/2/2^1/2. For 9b:

2

∆υ_AB) 142.7 Hz, J _AB) 13.0 Hz, T_c) 320 K. For 11b, ∆υ_AB) 159.1

Hz, J _AB) 13.5 Hz, T_c) 334 K. For 14a , ∆υ_AB) 31.1 Hz, J _AB) 10.7

Hz, T_c) 350 K. See: (b) Alexander, S. J . Chem. Phys. 1962, 37, 971.

(c) Kurland, R. J .; Rubin, M. B.; Wise, W. B. J . Chem. Phys. 1964, 40,

2426. (d) Kost, D.; Zeichner, A. Tetrahedron. Lett. 1974, 4533.

(40) It was not possible to determine racemization barriers for 10a

or 11a due to temperature-dependent ∆υ/J ratios.

Group 4 Metal Alkyl Complexes

Organometallics, Vol. 16, No. 15, 1997 3289

The facile migration of a benzyl group from Zr to C2′

in eq 8 reflects the nucleophilic character of the Zr-

CH₂Ph group and the electrophilic character of the C2

carbons of the MeBr₂Ox^-ligands. As noted above,

EHMO calculations reveal that the frontier orbitals of

(MeOx)₂ZrR₂species include low-lying empty orbitals

with significant orbital density at these carbons. This

rearrangement probably involves a simple intramolecu-

lar 1,3-suprafacial migration of the benzyl group, result-

ing in a single diastereomer of the product. The

apparent instability of (MeOx)₂ZrMe₂and (MeBr₂-

Ox)₂ZrMe₂noted above may be due to a similar but more

rapid rearrangement. The rate of alkyl migration

should be determined primarily by electronic factors in

these sterically open systems and is, therefore, expected

to vary in the order R ) H > alkyl > benzyl.^4e,32d,43

Similar rearrangements have been observed in re-

lated Zr(IV) systems. For example, Rothwell has re-

ported that the dibenzyl complex {2,6-(^tBu)₂-C₆H₃O}₂-

Zr(CH₂Ph)₂(bipy) rearranges at room temperature by

benzyl migration to a bipy R-carbon.⁴⁴Interestingly the

corresponding dimethyl complex does not rearrange

under these conditions, which suggests that relief of

steric crowding is an important driving force for this

process in these sterically congested species. Tetraaza

macrocycle complexes, such as (Me₄taa)ZrMe₂and (Me₄-

taen)ZrR₂, rearrange by alkyl migration from Zr to a

macrocycle imine carbon.⁴

Me′ resonance is shifted upfield into the aliphatic region

(δ 0.62) and is slightly broadened, suggesting the

existence of long range coupling. Two AB patterns are

observed for the -CH₂Ph groups of 19. One set (δ 2.86,

2.84, J _HH) 11.8) is assigned to the ZrCH₂Ph group. The

other set consists of two more widely separated doublets

(δ 3.31, 2.32, J _HH) 12.5), which are slightly broadened.

Significantly, the downfield doublet of this set exhibits

a COSY correlation with the Me′ group. These data are

consistent with the structure proposed for 19 in eq 8,

in which one benzyl group has migrated to C2′, such

that CH₂Ph′/Me′ H-H coupling is possible. The ¹³C

NMR spectrum of 19 confirms this proposed structure.

Two methylene ¹³C NMR resonances are observed: one

is assigned to the ZrCH₂Ph group on the basis of the

δ(C) (73.6) and J _CH(116 Hz) values, which are charac-

teristic of a normal ZrCH₂Ph group. The methylene

chemical shift (δ 48.3) and J _CH(126 Hz) values for the

other benzyl group are characteristic of an organic

benzyl group and consistent with the values expected

for the migrated benzyl group in 19. Additionally, a

quaternary carbon resonance is observed at δ 61.5 which

is assigned to C2′. The chemical shifts for the migrated

CH₂Ph′ methylene carbon and C2′ agree well with the

values predicted using standard ¹³C NMR chemical shift

additivity rules.⁴¹

Syn th esis of (Ox)₂M(R)⁺Com p lexes. In initial

efforts to generate (MeOx)₂Zr(R)⁺cations, the reactions

of 9a and 9b with [HNMe₂Ph][B(C₆F₅)₄] were investi-

1

gated by H NMR spectroscopy (eq 9).^6a,45These reac-

tions proceed rapidly (<10 min) and quantitatively in

methylene chloride at 23 °C, yielding the base-free

cations (MeOx)₂Zr(CH₂Ph)⁺(20a ) and (MeOx)₂Zr(CH₂-

CMe₃)⁺(20b), which are described in detail below, as

The data for 19 do not allow assignment of the

coordination geometry. However, the distorted trigonal

bipyramidal structure shown in eq 8 is reasonable,

requires minimal structural rearrangement from 11a ,

and allows for effective π-donation from the amide

function to the Zr eq acceptor orbital.⁴²

(43) Alelyunas, Y. W.; Guo, Z.; LaPointe, R. E.; J ordan, R. F.

Organometallics 1993, 12, 544.

(44) Kobriger, L. M.; McMullen, A. K.; Fanwick, P. E.; Rothwell, I.

P. Polyhedron 1989, 8, 77.

+

-

(45) For the use of HNR₃reagents and the B(C₆F₅)₄counterion

in the generation of L_nM(R)⁺reagents, see refs 1-11 and (a) Boch-

mann, M.; Wilson, L. M. J . Chem. Soc., Chem. Commun. 1986, 1610.

(b) Lin, Z.; Le Marechal, J .; Sabat, M.; Marks, T. J . J . Am. Chem. Soc.

1987, 109, 4127. (c) Turner, H. W.; Hlatky, G. G. Eur. Pat. Appl. 0

277 003, 1988. (d) Hlatky, G. G.; Turner, H. W.; Eckman, R. R. J . Am.

Chem. Soc. 1989, 111, 2728. (e) Turner, H. W. Eur. Pat. Appl. 0 277

004, 1988. (f) Hlatky, G. G.; Eckman, R. R.; Turner, H. W. Organo-

metallics 1992, 11, 1413. (g) Eshuis, J . J . W.; Tan, Y. Y.; Meetsma, A.;

Teuben, J . H.; Renkema, J .; Evens, G. G. Organometallics 1992, 11,

362. (h) Eshuis, J . J . W.; Tan, Y. Y.; Renkema, J .; Teuben, J . H. J .

Mol. Catal. 1990, 62, 277. (i) Amorose, D. M.; Lee, R. A.; Petersen, J .

L. Organometallics 1991, 10, 2191. (j) Horton, A. D.; Orpen, A. G.

Organometallics 1991, 10, 3910. (k) Bochmann, M.; J aggar, A. J .;

Nicholls, J . C. Angew. Chem., Int. Ed. Engl. 1990, 29, 780. (l) Horton,

A. D.; Frijins, J . H. G. Angew. Chem., Int. Ed. Engl. 1991, 30, 1152.

(m) Grossman, R. B.; Doyle, R. A.; Buchwald, S. L. Organometallics

1991, 10, 1501. (n) Bochmann, M.; Lancaster, S. J . J . Organomet.

Chem. 1992, 434, C1. (o) Ewen, J . A.; Elder, M. J .; J ones, R. L.;

Haspeslagh, L.; Atwood, J . L.; Bott, S. G.; Robinson, K. Makromol.

Chem., Macromol. Symp. 1991, 48/ 49, 253.

(41) Chemical shifts calculated for the model compound I are, as

follows: C2, δ 66.4; CH₂Ph, δ 44.2. These values agree well with those

observed for the analogous carbons of rearrangement product 19.

Comparison of ¹³C NMR chemical shift values for methyl groups in

simple methylamines and ZrNMe₂compounds shows that replacement

of the NMe group by Zr will change δ C2 by <5 ppm. Chemical shifts

were calculated using the method and parameters given in the

following: Atta-Ur-Rahman, Nuclear Magnetic Resonance; Springer-

Verlag: New York, 1986; pp 149-152.

(42) Albright, T. A.; Burdett, J . K.; Whangbo, M. Orbital Interactions

in Chemistry; J ohn Wiley & Son: New York, 1985; p 320.

3290 Organometallics, Vol. 16, No. 15, 1997

Bei et al.

the B(C₆F₅)₄^-salts. The amine coproduct NMe₂Ph does

not coordinate to these cations at room temperature.

In contrast, the reaction of 11a and [HNMe₂Ph]-

[B(C₆F₅)₄] yields the amine adduct (MeBr₂Ox)₂Zr(CH₂-

Ph)(NMe₂Ph)⁺(21a , eq 10). Below -40 °C, the ¹H NMR

F igu r e 4. Molecular structure of the (MeBr₂Ox)₂Zr(η²-

CH₂Ph)⁺cation of 23a .

spectra of 21a contain two sets of MeBr₂Ox^-resonances,

an AB pattern for the ZrCH₂unit, and two NMe₂Ph

methyl resonances (1/1 intensity ratio), indicating that

the coordinated NMe₂Ph does not exchange on the NMR

time scale in this temperature range. However, at room

temperature, broad singlets are observed for the

MeBr₂Ox^-and NMe₂Ph groups, indicating that amine

exchange is rapid on the NMR time scale. The forma-

tion of NMe₂Ph adduct 21a indicates that (MeBr₂-

Ox)₂Zr(CH₂Ph)⁺is a stronger Lewis acid than nonbro-

minated analogue 20a , as expected due to the electron-

withdrawing effect of the Br substituents. Complex 21a

decomposes at room temperature in CD₂Cl₂and was not

isolated.⁴⁶Similarly, the reaction of 14a with [HNMe₂-

Ph][B(C₆F₅)₄] yields the labile amine adduct [(MeBr₂-

Ox)₂Hf(CH₂Ph)(NMe₂Ph)][B(C₆F₅)₄].

F igu r e 5. Alternate view of the structure of the (MeBr₂-

Ox)₂Zr(η²-CH₂Ph)⁺cation of 23a .

20b, 22a , 23a , and 24a , which separate from the

reaction mixtures as oils and can be isolated as yellow

solids by separation from the supernatants, trituration

with benzene, and drying under vacuum. These salts

are stable in CH₂Cl₂and were characterized by NMR

spectroscopy; additionally, satisfactory elemental analy-

ses were obtained for 22a , 23a , and 24a . Recrystalli-

zation of these [(Ox)₂MR][B(C₆F₅)₄] compounds is diffi-

cult due to their high solubility in chlorinated solvents

and tendency to “oil out” of hydrocarbon solvents or

mixtures of chlorinated and hydrocarbon solvents.

However, [(MeBr₂Ox)₂Zr(η²-CH₂Ph)][B(C₆F₅)₄] (23a) was

successfully recrystallized from CH₂Cl₂and character-

ized by X-ray diffraction.

To simplify the isolation of base-free (Ox)₂M(R)⁺

species and to avoid the formation of amine coordina-

tion, we investigated the reactions of (Ox)₂MR₂com-

plexes with the bulkier, more acidic ammonium salt

[HNMePh₂][B(C₆F₅)₄] (eq 11).^6aIn benzene or toluene,

X-r a y Str u ctu r e of [(MeBr ₂Ox)₂Zr (η²-CH₂P h )]-

[B(C₆F ₅)₄] (23a ). Complex 23a crystallizes as discrete

ions. The anion structure is normal. The molecular

structure of the (MeBr₂Ox)₂Zr(η²-CH₂Ph)⁺cation is

illustrated in Figures 4 and 5, and important bond

distances and angles are listed in Table 2. The (MeBr₂-

Ox)₂Zr(η²-CH₂Ph)⁺cation adopts a distorted square

pyramidal structure in which the η²-benzyl ligand

occupies the apical site and the MeBr₂Ox^-ligands

occupy the basal sites in a trans-O, trans-N arrange-

ment. The apical-Zr-basal angles between the cen-

troid of the C(47)-C(41) bond and the basal O and N

donor atoms are all 111 ( 4°, and the trans O-Zr-O

and N-Zr-N angles are 137.0(1)° and 138.1(1)°, re-

spectively. The Zr-ligand distances in 23a are 0.05-

0.1 Å shorter than the corresponding distances in

neutral dibenzyl complex 9a . The η²-benzyl ligand is

these reactions yield [(Ox)₂M(R)][B(C₆F₅)₄] salts 20a ,

(46) The decomposition of 21a in CD₂Cl₂probably proceeds by the

same type of mechanism as proposed for (acen)Zr(R)(NR′₃)⁺species.

See ref 6a for details.

Group 4 Metal Alkyl Complexes

Organometallics, Vol. 16, No. 15, 1997 3291

Ta ble 2. Selected Bon d Dista n ces (Å) a n d Bon d

An gles (d eg) for

[(MeBr ₂Ox)₂Zr (η²-CH₂P h )][B(C₆F ₅)₄] (23a )

Zr-O(1)

Zr-O(21)

Zr-N(3)

1.992(3)

2.006(3)

2.340(4)

Zr-N(23)

Zr-C(41)

Zr-C(47)

2.353(4)

2.448(5)

2.245(6)

O(1)-Zr-O(21)

O(1)-Zr-N(3)

O(1)-Zr-N(23)

O(1)-Zr-C(41)

O(1)-Zr-C(47)

O(21)-Zr-N(23)

O(21)-Zr-N(3)

O(21)-Zr-C(41)

O(21)-Zr-C(47)

137.0(1)

73.7(1)

94.4(1)

114.3(2)

112.5(2)

74.4(1)

87.3(1)

107.9(2)

106.3(2)

N(3)-Zr-N(23)

N(3)-Zr-C(41)

N(3)-Zr-C(47)

N(23)-Zr-C(41)

N(23)-Zr-C(47)

Zr-C(47)-C(41)

Zr-O(1)-C(1)

138.1(1)

127.6(2)

92.4(2)

94.1(2)

128.6(2)

80.0(3)

123.4(3)

121.0(3)

Zr-O(21)-C(21)

oriented such that the Ph ring lies over the Zr-N(23)

bond (see Figure 5).

The benzyl ligand in 23a is highly distorted, as is

evident from the very acute Zr-C(47)-C(41) bond angle

(80.0(3)°) and short Zr-C(41) contact (2.448(5) Å). The

extent of distortion, i.e., the strength of the Zr‚‚‚Ph

interaction, in 23a is clearly much greater than that in

9a , as expected from the increased metal charge. The

benzyl ligand in 23a is significantly more distorted than

those in the metallocene complexes Cp₂Zr(η²-CH₂Ph)-

(CH₃CN)⁺(Zr-C-C 84.9(4)°; Zr-C_ipso, 2.648(6) Å) and

rac-(EBTHI)Zr(η²-CH₂Ph)(CH₃CN)⁺(Zr-C-C, 84.4(5)°;

Zr-C_ipso, 2.627(9) Å).^32e,gThe Zr-CH₂bond in 23a

(2.245(6) Å) is significantly shorter than those in Cp₂-

Zr(η²-CH₂Ph)(CH₃CN)⁺(2.344(8) Å) and rac-(EBTHI)-

Zr(η²-CH₂Ph)(CH₃CN)⁺(2.321(9) Å).

The structures of cation 23a and its neutral precursor

11a are formally related as shown in eq 12. Loss of one

F igu r e 6. Schematic illustration of the frontier orbitals

of the model compound (MeBr₂Ox)₂ZrMe⁺, derived from

23a by replacement of the benzyl phenyl ring with a

hydrogen, as determined by an EHMO analysis.

benzyl ligand generates a square pyramidal species with

a MeBr₂Ox^-nitrogen in the apical site. A simple shift

of the other MeBr₂Ox^-nitrogen by ca. 90° generates the

observed structure of 23a .

mized when the benzyl is oriented such that the phenyl

ring lies flat over a Zr-N bond. Note that that, as for

(MeBr₂Ox)₂ZrMe₂, the precise ordering of the LUMOs

is sensitive to the computational method and the

parameters used.

Electr on ic Str u ctu r e of 23a . To probe the origin

of the η²-bonding mode and the orientational preference

of the benzyl ligand in 23a , the frontier orbitals of the

model species (MeBr₂Ox)₂Zr(Me)⁺(given the same

geometry as 23a ) were investigated by an EHMO

analysis (Figure 6).⁴⁷The two lowest unoccupied orbit-

als are MeBr₂Ox^--based π* antibonding orbitals which

are primarily localized on N, C2, and C4 (see Chart 1

for numbering) and are similar to the LUMOs of

(MeOx)₂ZrMe₂(Figure 2). Slightly above these orbitals

lie the empty d_xy, d_xz, and d_yzorbitals, the latter of which

is raised in energy due to π-donation from the MeBr₂Ox^-

oxygens. Of these three acceptor orbitals, d_xzis geo-

metrically and energetically best suited for overlap with

the benzyl Ψ_πdonor orbital in the corresponding η²-

benzyl complex 23a . The Ψ_π/d_xzinteraction is maxi-

Solu tion Str u ctu r e a n d Dyn a m ic Beh a vior of

(MeBr ₂Ox)₂M(CH₂P h )⁺(M ) Zr , Hf). The solution

structures and dynamic behavior of (MeBr₂Ox)₂M(η²-

CH₂Ph)⁺complexes 23a and 24a have been probed by

NMR spectroscopy. The ZrCH₂J _HH(8.6 Hz) and J _CH

(145 Hz) values for 23a establish that the η²-benzyl

interaction observed in the solid state is maintained in

solution. The -85 °C ¹H NMR spectrum of 23a (Figures

7 and 8) contains two sets of MeBr₂Ox^-resonances, two

sets of o-Ph and m-Ph resonances, a single p-Ph

resonance, and an AB pattern for the ZrCH₂unit. This

spectrum shows that the molecular symmetry is C₁, the

two MeBr₂Ox^-ligands are inequivalent, and the sides

of the Zr(η²-CH₂Ph) phenyl ring are inequivalent. The

low-temperature (-85 °C) ¹⁹F and ¹³C NMR spectra of

23a show no evidence for B(C₆F₅)₄^-or CD₂Cl₂coordina-

tion, although the latter is expected to be difficult to

(47) The model species (MeBr₂Ox)₂Zr(Me)⁺was constructed from the

structure of 23a by replacing the phenyl group of the benzyl ligand

with a hydrogen.

3292 Organometallics, Vol. 16, No. 15, 1997

Bei et al.

Sch em e 2

As the sample temperature is raised from -85 °C, two

dynamic processes can be detected for 23a ; these are

illustrated schematically in Scheme 2. The lower

energy process (process i) causes the MeBr₂Ox^-reso-

nances to broaden and ultimately coalesce by ca. -60

°C, but does not perturb the Zr(η²-CH₂Ph) resonances

(see Figures 7 and 8). This process is identified as

rotation of the benzyl ligand around the Zr-C bond (and

between two equivalent sites) without cleavage of the

η²-interaction which, as shown in Scheme 2, renders the

MeBr₂Ox^-ligands equivalent but not the sides of the

Ph ring or the ZrCH₂hydrogens. Above -20 °C, a

second, higher energy process (ii) is detected which

results in broadening of the o-Ph and m-Ph resonances

of the ZrCH₂Ph group (see Figure 7). The o-Ph reso-

nances coalesce at 27 °C, while the m-Ph resonances

are still broadened into the base line at 40 °C, the

highest temperature studied. This higher energy pro-

cess is identified as rotation around the ZrCH₂-Ph

bond, which likely proceeds via isomerization of 23a to

a Zr(η¹-CH₂Ph) intermediate in which essentially free

rotation about the ZrCH₂-Ph bond can occur, rendering

the sides of the Ph group equivalent. Note that as the

η¹-CH₂Ph intermediate can collapse to the η²-CH₂Ph

ground state species by coordination of either face of

the Ph ring, the η²-η¹isomerization rate is twice the

rate of exchange of the o-Ph or m-Ph hydrogens. The

barriers for these processes will be discussed below. At

40 °C, a sharp AB pattern is observed for the ZrCH₂Ph

methylene hydrogens, indicating the inversion of the

metal configuration (process iii), which results in net

exchange of the benzyl ligand between the top and

bottom faces of the (MeBr₂Ox)₂Zr²⁺fragment, is still

slow on the NMR time scale at this temperature.

The NMR properties of hafnium benzyl cation 24a are

very similar to those of 23a . The J _CHvalue (143 Hz)

for the HfCH₂group establishes that the η²-benzyl

F igu r e 7. Variable-temperature NMR spectra of [(MeBr₂-

Ox)₂Zr(η²-CH₂Ph)][B(C₆F₅)₄] (23a ). The aromatic region is

shown. Assignments at -85 °C are as follows: δ 8.7 (H4),

8.5 (H4), 8.0 (H6), 7.95 (H6), 7.8 (H3, ∆), 7.7 (m-Ph, b), 7.6

(H3, 4), 7.0 (o-Ph, *), 6.8 (o-Ph, *), 6.7 (p-Ph), 6.6 (m-Ph,

b). The signals at δ 7.32 and 7.06-7.25 are due to benzene

and toluene respectively.

F igu r e 8. Variable-temperature NMR spectra of [(MeBr₂-

Ox)₂Zr(η²-CH₂Ph)][B(C₆F₅)₄] (23a ). The aliphatic region is

shown. In the -85 °C spectrum, the AB pattern centered

at δ 3.5 is due to the diastereotopic ZrCH₂hydrogens and

the singlets at δ 3.4 and 2.8 are due to the MeBr₂Ox

hydrogens.

1

interaction is maintained in solution. The -90 °C H

NMR spectrum contains two broad methyl signals, a

single set of broad aryl resonances for the MeBr₂Ox^-

ligands, and two sharp sets of o-Ph and m-Ph signals,

a p-Ph resonance, and a HfCH₂AB pattern for the

benzyl ligand. This spectrum is consistent with a C₁-

symmetric square pyramidal structure analogous to that

observed for 23a and indicates that the benzyl rotation

detect.⁴⁸These observations imply that 23a retains its

solid state structure and is rigid on the NMR time scale

at -85 °C in CD₂Cl₂solution.

(48) Fernandez, J . M.; Gladysz, J . A. Organometallics 1989, 8, 207.

Group 4 Metal Alkyl Complexes

Organometallics, Vol. 16, No. 15, 1997 3293

1

process (i) which renders the MeBr₂Ox^-ligands equiva-

lent is not completely frozen out at this temperature.

The two MeBr₂Ox^-resonances coalesce at -78 °C, and

all of the MeBr₂Ox^-resonances are sharp by -30 °C.

The HfCH₂Ph o-Ph resonances coalesce at -22 °C, and

the m-Ph resonances coalesce at 10 °C, due to the higher

energy η²-η¹isomerization process (ii). The room-

24a discussed above. The room-temperature H NMR

spectrum of (MeOx)₂Zr(CH₂Ph)⁺(20a ) contains two sets

of MeOx^-resonances, an AB pattern for the ZrCH₂unit,

and a single set of ZrCH₂Ph resonances. As the tem-

perature is lowered, the MeOx^-resonances remain

sharp but the ZrCH₂Ph resonances broaden; in particu-

lar, the o-Ph and m-Ph resonances broaden significantly

below -50 °C and are broadened into the base line at

-85 °C, the lowest temperature at which spectra were

recorded.⁵³The J _HH(9.6 Hz) and J _CH(132 Hz) values

for 20a indicate that the benzyl ligand in this species

has some η²character but is less distorted than the

1

temperature H NMR spectrum of 24a exhibits an AB

pattern for the HfCH₂unit, indicating that as for 23a ,

inversion of the metal configuration (process iii) is slow

on the NMR time scale at this temperature. This AB

pattern broadens significantly above 85 °C (C₆D₅Cl),

indicating that inversion of the metal configuration

becomes rapid on the NMR time scale in this temper-

ature range. However, sample decomposition also oc-

curs at 85 °C.

1

benzyl ligand in 23a . The room-temperature H NMR

spectrum of (MeOx)₂Hf(CH₂Ph)⁺(22a ) is similar to that

of 20a and contains two sets of MeOx^-resonances and

one set of HfCH₂Ph resonances. However, the HfCH₂-

Ph J _HH(11.3 Hz) and J _CH(125 Hz) values indicate that

the benzyl ligand is not significantly distorted. These

NMR data for 20a and 22a are inconsistent with the

square pyramidal structure and the dynamic processes

observed for 23a and 24a (Scheme 2) because (i) it is

very unlikely that the η²-η¹isomerization (which,

following rotation around the MCH₂-Ph bond, ex-

changes the sides of the MCH₂Ph group) would be faster

than rotation about the Zr-CH₂Ph bond (which ex-

changes the MeOx^-ligands) and (ii) in any case, the

Hf‚‚‚Ph interaction in 22a is clearly too weak to lock

the benzyl ligand in a conformation which results in

inequivalent MeOx^-ligands at room temperature.

Free energy barriers for the dynamic processes i-iii

1

observed for 23a and 24a were determined from the H

NMR line shape changes. The ∆G^q(rotation) values for

the benzyl group rotation (process i) are very similar

for the two compounds (23a , 9.8(1) kcal/mol; 24a , 9.2-

(2) kcal/mol).⁴⁹The Zr‚‚‚Ph interaction is not cleaved

during this exchange process but switches between the

d_xzand d_yzZr acceptor orbitals as the Ph is rotated over

the Zr-N and Zr-O bonds (see Figure 6). The barrier

is probably determined primarily by the difference in

energy between these orbitals, which is apparently

similar for the two species. In contrast, the η²-η¹

isomerization barrier ∆G^q(η²-η¹) (process ii) is signifi-

cantly higher for 23a (14.0(1) kcal/mol) than for 24a

(11.4(2) kcal/mol).⁵⁰As there should be little steric

hindrance to this process, this difference indicates that

the M‚‚‚Ph interaction is stronger in the Zr cation than

in the Hf analogue. Interestingly, the barrier estimated

for racemization of the five-coordinate cation 24a (pro-

cess iii, ∆G^q(racemization) > 20(1) kcal/mol) is higher

than that determined for the related neutral six-

coordinate dibenzyl complex 14a (17.3(1) kcal/mol).^51,52

A reasonable explanation for this difference is that the

rate-limiting step for both racemization processes is

dissociation of the nitrogen end of the MeBr₂Ox^-ligand,

which would be disfavored in the five-coordinate cation.

Solu tion Str u ctu r e a n d Dyn a m ics of (MeOx)₂M-

(R)⁺Com p lexes. The variable-temperature NMR

properties of the (MeOx)₂M(R)⁺cations are quite dif-

ferent from those of the brominated analogues 23a and

The room-temperature NMR spectrum of the neopen-

tyl complex (MeOx)₂Zr(CH₂CMe₃)⁺(20b) is similar to

those of 20a and 22a and indicates that this species has

a C₁symmetric structure with inequivalent MeOx^-

ligands. The J _CH(ZrCH₂) value (100 Hz) of 20b suggests

the existence of a Zr-H-CR agostic interaction in this

cation, although this issue was not probed in detail.^37,54

However, R-agostic interactions in related systems are

normally very weak, so it is unlikely that the inequiva-

lence of the MeOx^-ligands in this species results from

locking of the neopentyl ligand in a particular confor-

mation by a Zr-H-CR interaction.

Thus, the NMR properties of 20a , 20b, and 22a are

not easily rationalized in terms of square pyramidal

structures similar to those of 23a and 24a , in which a

nonclassical bonding interaction locks the apical hydro-

carbyl ligand in a particular orientation relative to the

Ox^-ligands. Low-temperature ¹⁹F NMR (22a ) and ¹³C

NMR (20a , 20b, 22a ) spectra show no evidence for the

existence of strong interactions between these cations

(49) Barriers for the benzyl rotation process (i) were calculated from

the coalesence of the MeBr₂Ox^-resonances and/or H4 resonances using

the standard formulae for a two-site, equal population exchange

process; i.e., T_c) coalesence temperature; k_c) exchange rate constant

at T_c) (2.22)(∆υ); ∆G^q) 4.576T_c(10.32 + log(T_c/k_c). For 23a : Me

coalesence ∆υ(Me) ) 199.7 Hz, k_c) 444 s^-1, T_c) 215(2) K, ∆G^q

-

and the B(C₆F₅)₄counterion or the CD₂Cl₂solvent. It

thus appears that the structures of the (MeOx)₂M(R)⁺

(rotation) ) 9.8(1) kcal/mol; H4 coalesence ∆υ(H4) ) 70.8 Hz, k_c

)

158 s^-1, T_c) 205(2) K, ∆G^q(rotation) ) 9.8(1) kcal/mol. For 24a : Me

coalesence ∆υ(Me) ) 176 Hz, k_c) 391 s^-1, T_c) 195(3) K, ∆G^q(rotation)

) 9.2(2) kcal/mol. The H4 resonances of 24a are not resolved at 188

K, the lowest temperature at which spectra could be obtained.

(50) Barriers for the exchange of the o-Ph hydrogens, ∆G^q(o-Ph

exchange), were calculated from the coalesence of the o-Ph resonances.

Barriers for η²-η¹isomerization ∆G^q(η²-η¹) were calculated by

assuming that k(η²-η¹) ) 2k(o-Ph exchange). For 23a : ∆υ(o-Ph) ) 96

Hz, k_c) 213 s^-1, T_c) 300(2) K, ∆G^q(o-Ph exchange) ) 14.2(1) kcal/

mol. For 24a : ∆υ(o-Ph) ) 155 Hz, k_c) 344 s^-1, T_c) 251(2) K, ∆G^q

(o-Ph exchange) ) 11.7(2) kcal/mol.

(53) Solubility limitations precluded experiments at lower temper-

atures, so ∆G^q(o-Ph exchange) and ∆G^q(m-Ph exchange) values could

not be determined.

(54) (a) Grubbs, R. H.; Coates, G. W. Acc. Chem. Res. 1996, 29, 85.

(b) McGrady, G. S.; Downs, A. J .; Hambin, J . M.; McKean, D. C.

Organometallics 1995, 14, 3783. (c) Leclerc, M. K.; Brintzinger, H. H.

J . Am. Chem. Soc. 1995, 117, 1651. (d) Barta, N. S.; Kirk, B. A.; Stille,

J . R. J . Am. Chem. Soc. 1994, 116, 8912. (e) Etienne, M.; Biasotto, F.;

Mathieu, R. J . Chem. Soc., Chem. Commun. 1994, 1661. (f) Etienne,

M. Organometallics 1994, 13, 410. (g) Mashima, K.; Nakamura, A. J .

Organomet. Chem. 1992, 428, 49. (h) Krauledat, H.; Brintzinger, H.

H. Angew. Chem., Int. Ed. Engl. 1990, 29, 1412. (i) Piers, W. E.;

Bercaw, J . E. J . Am. Chem. Soc. 1990, 112, 9406. (j) Brookhart, M.;

Green, M. L. H.; Wong, L. L. Prog. Inorg. Chem. 1986, 36, 1. (k)

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.

(51) Estimates for the racemization barrier for 24a based on line

broadening of the HfCH₂AB pattern at 373 K (∆G^q(racemization) ca.

20.8 kcal/mol) and 383 K (∆G^q(racemization) ca. 20.9 kcal/mol) and

comparison of experimental and simulated spectra (DNMR5, ∆G^q

(racemization) ca. 20.7 kcal/mol) are in the range of 21 kcal/mol.

(52) The racemization barrier for 23a could not be determined

because ∆υ for the ZrCH₂AB pattern changes significantly with

temperature and is very small above 25 °C.

3294 Organometallics, Vol. 16, No. 15, 1997

Bei et al.

Ch a r t 3

Ch a r t 4

field and one normal MeOx resonance, which indicates

that the arrangement of MeOx ligands is similar to that

for 22a .

The proposed structure for 22a accommodates the

variable-temperature NMR results. The inequivalence

of the two quinolinolato ligands results from their

geometric relationship, not from a fixed orientation of

the hydrocarbyl ligand. Therefore, neither rotation

around the Hf-CH₂Ph bond nor η²-η¹benzyl isomer-

ization render the MeOx and MeOx′ ligands equivalent.

The proposed structure for (MeOx)₂M(R)⁺complexes

is formally related to the structure of the neutral

(MeOx)₂MR₂precursors, as shown in eq 13. Alkyl

cations 20a ,b and 22a are fundamentally different from

those of (MeBr₂Ox)₂M(R)⁺cations 23a and 24a .

To better understand the solution structures of these

(MeOx)₂MR⁺complexes, we investigated the structure

of 22a in more detail. A complete assignment of the

¹H NMR spectrum, including resonances for the two

inequivalent MeOx^-ligands (labeled MeOx and MeOX′

in Chart 3) and the benzyl group was developed based

on room-temperature 2-D COSY and NOESY experi-

ments, and geometric information was obtained from

the 2-D NOESY spectrum. Two key observations

provide important information about the structure of

22a . (i) NOESY correlations are observed between the

o-Ph (benzyl) and Me hydrogens, the m-Ph (benzyl) and

Me hydrogens, and H7 and one of the HfCH₂hydrogens.

These correlations establish that the MeOx ligand is

spatially close to the CH₂Ph ligand. However, no

NOESY correlations are observed between the MeOx′

hydrogens and the HfCH₂Ph hydrogens. (ii) The Me′

resonance (δ ) 0.59) is shifted ca. 2 ppm upfield from

the range normally observed for (MeOx)₂MX₂complexes.

This unusual effect could be due to anisotropic shielding

by the HfCH₂Ph phenyl group. However, as noted

above, NOESY correlations between the Me′ and HfCH₂-

Ph hydrogens are not observed. Moreover, a similar

high-field Me resonance is observed for (MeOx)₂Zr(CH₂-

CMe₃)⁺(20b), which does not contain a benzyl ligand.

Therefore, the high-field shift of the Me′ resonance for

22a (and 20b) must result from anisotropic shielding

by the MeOx ligand; i.e., the Me′ group lies within the

shielding region of the MeOx ligand. On the basis of

these observations, we propose that 22a adopts the

structure shown in Chart 3, which may be described as

a distorted square pyramid with the MeOx^-oxygen in

the apical position and a cis arrangement of basal

nitrogen ligands. Alternatively, this structure may be

described as a distorted trigonal bipyramid with apical

benzyl and quinolinolato nitrogen ligands. Cations 20a

and 20b are assigned analogous structures on the basis

of the similarity of their NMR spectra to the spectra of

22a ; in particular, both 20a and 20b exhibit one high-

abstraction yields a five-coordinate species, which can

relax to the proposed structure by a shift of one of the

MeOx^-oxygen donors.

The structural difference between the (MeBr₂Ox)₂MR⁺

(23a , 24a ) and (MeOx)₂MR⁺(20a , 20b, 22a ) cations may

be rationalized in terms of electronic effects. As noted

above, the (MeBr₂Ox)₂M(CH₂Ph)⁺cations 23a and 24a

adopt square pyramidal structures with an apical-

benzyl, trans-O, trans-N ligand arrangement. A key

feature of this structure is that the potential π-donor

phenoxides must share a single metal π-acceptor orbital

(d_yz, Figure 6). This structure is disfavored for (MeOx)₂-

M(R)⁺species 20a , 20b, and 22a because the oxygens

in the MeOx^-ligand are stronger π-donors than those

in the MeBr₂Ox^-ligand. In the proposed apical-O, cis-N

structure in Chart 3, the two quinolinolato oxygens do

not compete for the same metal d acceptor orbital; i.e.,

the apical oxygen can form a O-Zr π-bond with the d_yz

orbital, and the basal oxygen can form an O-Zr π-bond

with the d_xzorbital (using the coordinate system in

Chart 3).

Alter n a tive Str u ctu r a l P ossibilities for (MeOx)₂-

M(R)⁺Com p lexes. Two other possible structures (A

and B in Chart 4) were considered for 20a ,b and 22a

but were ruled out on the basis of NMR observations.

Structure A, in which the MeOx′ ligand is oriented in a

different manner than that in the proposed structures

of 20a ,b and 22a , is inconsistent with the observation

Group 4 Metal Alkyl Complexes

Organometallics, Vol. 16, No. 15, 1997 3295

Ch a r t 5^a

spectroscopy) implies that the amine and benzyl ligand

are cis because the possible trans structures C and D

have C₂and C_ssymmetry, assuming free rotation about

the Zr-amine and Zr-C bonds. However, the data for

21a do not establish the orientations of the MeBr₂Ox^-

ligands, and due to overlap among the NMe₂Ph and

CH₂Ph resonances, details about the orientation and

dynamics of the benzyl ligands are unknown.

To further probe the structures of (Ox)₂M(R)(L)⁺

species, the more stable PMe₃adducts 25a and 26a were

1

prepared (eq 14). The H NMR spectra of 25a and 26a

a

5,7 Ox substituents omitted.

of NOESY correlations between the benzyl ligand and

only one of the MeOx^-ligands and does not provide a

rationale for the high-field shift of one of the Me

resonances. This structure is disfavored because the

two quinolinolato oxygens compete for the same metal

d orbital for O-M π-donation and because the strong

trans-influence hydrocarbyl and MeOx′ oxygen ligands

are in a trans orientation. Structure B, which is the

cis isomer of the structures of 23a and 24a , contains

two equivalent MeOx^-ligands and is thus inconsistent

with the C₁symmetry of these complexes implied by the

NMR data. Inspection of models suggests that this

structure is disfavored by unfavorable steric interactions

between the two MeOx^-methyl groups. However,

displacement of one MeOx^-pyridine to a position trans

to the benzyl group in B would relieve Me/Me steric

interactions and result in the structures proposed in

Chart 3.⁵⁵

Syn th esis an d Ch ar acter ization of [(MeBr ₂Ox)₂M-

(CH₂P h )(P Me₃)][B(C₆F ₅)₄] Com p lexes. The six pos-

sible isomers of a (Ox)₂M(R)(L)⁺complex (8 and C-G)

are illustrated in Chart 5. As noted in the introduction,

a key consideration in the choice of the (Ox)₂M(R)⁺

system for the development of new electrophilic metal

alkyl reagents/catalysts was the expectation that these

species would coordinate ligands or potential substrates

in a position cis to the hydrocarbyl ligand; i.e., that

(Ox)₂M(R)(L)⁺species would adopt structures of type 8

which are analogous to the structures of (Ox)₂MR₂

compounds. A cis relationship of the R and substrate

groups is necessary for subsequent insertion or σ-bond

metathesis reactions.

establish that both cations contain 1 equiv of PMe₃and

that PMe₃exchange is slow on the NMR time scale at

room temperature.

1

The H NMR spectrum of 25a is unchanged over the

temperature range from -80 to 25 °C and establishes

that this species has C₁symmetry. This conclusion is

confirmed by the ¹³C NMR spectrum. The ¹H spectrum

contains two sets of MeBr₂Ox^-resonances, showing that

the two ligands are inequivalent, and two sets of m-Ph

and o-Ph ZrCH₂Ph resonances, indicating that the sides

of the benzyl phenyl ring are inequivalent. All of the

¹H NMR resonances were assigned by 2-D COSY and

NOESY spectroscopy (-80 °C). The ZrCH₂J _HH(7.5 Hz)

and J _CH(145 Hz) values establish that the benzyl ligand

is coordinated in an η²mode, and the fact that the sides

of the benzyl phenyl ring are inequivalent indicates that

the η²-η¹exchange is slow on the NMR time scale. For

d⁰group 4 metal phosphine alkyl complexes, J _PHvalues

(P-M-CH) are similar for both cis and trans structures

(0-14 Hz) while J _PCvalues (P-M-CH) are small for

cis structures (<5 Hz) but much larger for trans

structures (>30 Hz).^56,57The J _PH(9.4, 5.0 Hz) and J _PC

(9 Hz) values for 25a are, thus, most consistent with a

structure in which the benzyl and PMe₃ligands are cis.

(56) Representative J _PHand J _PC(P-M-CH) values group 4 metal

complexes (a). TiCl₃(dmpe)Me: J _PH(cis) ) J _PH(trans) ) 7.7 Hz, J _PC

(cis) not observed, J _PC(trans) ) 32.4 Hz. TiCl₃(dmpe)Et: J _PH(cis), J _PH

-

The C₁symmetry of the amine complex (MeBr₂-

(trans) ) 12.0 Hz and unresolved, J _PC(cis) ) 3.1 Hz, J _PC(trans) ) 31.8

Hz. See ref 54k. (b) Zr(CH₂SiMe₂NSiMe₃)₂(dmpe): J _PH(cis) ) 3.2, 3.2

Hz, J _PC(cis) ) “on the order of the natural line width.” Planalp, R. P.;

Andersen, R. A. Organometallics 1983, 2, 1675. (c) TiMe₂(CH₂CH₂)-

(η²-dmpe)(η¹-dmpe): J _PH(cis) ) 4.5 Hz, J _PC(cis) not observed. Spencer,

M. D.; Morse, P. M.; Wilson, S. R.; Girolami, G. S. J . Am. Chem. Soc.

1993, 115, 2057.

Ox)₂Zr(CH₂Ph)(NMe₂Ph)⁺(21a ) (as determined by NMR

(55) The apical-R, trans-O, trans-N square pyramidal structure may

be less sterically congested than structures A or B and is, thus, favored

for (MeBr₂Ox)₂M(R)⁺species in which O-Zr π-bonding is not impor-

tant.

3296 Organometallics, Vol. 16, No. 15, 1997

Ta ble 3. Eth ylen e P olym er iza tion Da ta ^a

Bei et al.

µmol of

solvent

(mL)

time temp

yield

(g)

activity

(kg/mol‚atm‚h)

entry

catalyst

catalyst cocatalyst^bcocatalyst

(h)

(°C)

1^c,d(MeOx)₂Zr(CH₂Ph)₂(9a )

32

33

17

16

17

44

HNMe₂Ph⁺

31

29

17

16

17

44

1/1 C₆H₅Cl/toluene (20) 0.5

23

60

23

60

30

0.0

0.49(7)

0.69(1)

0.57(3)

0.41

0.19

0.1

0.05(1)

0.18(1)

0.57(5)

3.2

2^c

3^e

(MeOx)₂Zr(CH₂CMe₃)₂(9b)

(MeBr₂Ox)₂Zr(CH₂Ph)₂(11a )

0.5

19(3)

28(1)

22(1)

26^f

12

6.2

4^e

HMePh₂

+

5^e

6^c

7^c

toluene (20)

C₆H₅Cl (20)

0.5

8^c

9^e

(MeBr₂Ox)₂Hf(CH₂Ph)₂(14a )

HNMe₂Ph⁺

1/1 C₆H₅Cl/toluene (20) 0.5

1.9(5)

6.8(3)

22(3)

9.1^h

4.2ⁱ

10^e

11^e

12^g

13^g

14^j

15^g

HNMePh₂

0.5

+

(MeBr₂Ox)₂Zr(CH₂Ph)₂(11a )

(MeBr₂Ox)₂ZrCl₂(16)

HNMe₂Ph⁺

B(C₆F₅)₃

MAO

toluene (500)

1.0

1.5

0.67

14.6

30000

44

1.9^k

41^l

HNMe₂Ph⁺

.

^cCatalyst

a

b

-

Yields and activities for entries 3-5 and 9-11 are averages of 2-4 experiments. Anion of HNR₃⁺cocatalysis is B(C₆F₅)₄

d

and cocatalyst were mixed in the solvent (10 min) and then charged with 2 atm of ethylene. Similar results (i.e., no activity) were

obtained in pure C₆H₅Cl solution at 23 and 55 °C. ^eCatalyst and cocatalyst were mixed in the solvent (10 min) and then charged with 3

g

h

atm of ethylene. ^fM_n) 576, M_w/M_n) 1.18. TIBA (750 µmol, Al/Zr ) 17) added. Ethylene pressure ) 8 atm. M_n) 2.11 × 10⁴, M_w/M_n

i

j

k

l

) 16.3. M_n) 4.8 × 10⁴, M_w/M_n) 13.9. Ethylene pressure ) 8 atm. M_w) 4.6 × 10⁵(light scattering). M_w> 2 × 10⁶(light scattering).

Four isomers with cis benzyl and PMe₃groups are

possible for (Ox)₂M(CH₂Ph)(PMe₃)⁺species: the trans-

O, cis-N structure 25a shown in eq 14 (i.e., a type 8

structure) and E-G in Chart 5 which differ in the

arrangement of N and O ligands. The 2-D NOESY

spectrum for 25a shows a strong correlation between a

m-Ph resonance and a MeBr₂Ox^-resonance, indicating

that the benzyl Ph ring points toward a MeBr₂Ox^-

ligand and away from the PMe₃group. No other

interligand correlations are observed. Additionally,

both MeBr₂Ox^-resonances appear in the normal range

(δ 2.25, 2.02). These observations are consistent with

the structure 25a (eq 14; identical to 8, Chart 5) but

are inconsistent with structures E-G. In E and F , one

Ox methyl group lies within the shielding region of the

other Ox^-ligand (that containing Me′) so that one Me

resonance should appear at high field, as observed for

20a , 20b, and 22a . For F and G, a ZrCH₂/Me′ NOESY

correlation is expected since these groups are forced

close together in the expected most stable conformation.

Therefore, it is concluded that 25a adopts the trans-O,

cis-N structure shown in eq 14.

analogous base-free cation 24a (11.7(2) kcal/mol). As

the Hf‚‚‚Ph interaction is expected to be stronger in

base-free 24a than in PMe₃adduct 26a , the higher

barrier in the latter species probably results from steric

crowding between the benzyl and PMe₃ligands, which

restricts the mobility of the benzyl group.

Recently, Floriani showed that (hydroxyphenyloxa-

zolinato)₂M(CH₂Ph)₂and (hydroxyphenyloxazolinato)₂Hf-

(CH₂Ph)(THF)⁺(M ) Zr, Hf) adopt structures analogous

to those observed here for (Ox)₂M(CH₂Ph)₂and (Ox)₂M-

(CH₂Ph)(L)⁺species.⁶

Olefin P olym er iza tion Stu d ies. The foregoing

sections describe the synthesis and structures of a new

class of d⁰metal alkyl cations which incorporate the key

features believed to be required for olefin polymerization

and other “electrophilic metal alkyl” reactivity. Accord-

ingly, we have investigated the ethylene polymerization

reactivity of selected (MeOx)₂Zr(R)⁺(20a , R ) CH₂Ph;

20b, R ) CH₂CMe₃) and (MeBr₂Ox)₂M(CH₂Ph)⁺(23a ,

M ) Zr; 24a ; M ) Hf) complexes. These cationic species

were generated in situ from the appropriate (Ox)₂MR₂

precursors via the protonolysis reactions in eq 9 (20a ,b)

or eq 11 (23a , 24a ) and their ethylene polymerization

behavior compared under similar conditions (toluene/

chlorobenzene 1/1 by volume, 23 °C, 2-3 atm, 30 min

polymerization time). As summarized in Table 3, at 23

°C under these conditions the ethylene polymerization

activity order is 23a > 24a >> 20a ,b (not active) i.e.,

only the cations containing MeBr₂Ox^-ligands are active

(compare entries 1, 2, 4, 10). When the polymerization

temperature is raised to 60 °C, the activity of 23a

decreases (entry 5) and that of 24a increases (entry 11),

such that these catalysts exhibit comparable activities

at this temperature.

1

The H NMR spectrum of (MeBr₂Ox)₂Hf(η²-CH₂Ph)-

(PMe₃)⁺(26a ) is similar to that of 25a below -30 °C.

Above this temperature, however, the two o-Ph reso-

nances and the two m-Ph resonances for the benzyl

phenyl group broaden, ultimately coalescing at 25 and

30 °C, respectively. The resonances for the two in-

equivalent MeBr₂Ox^-ligands do not broaden up to 40

°C, the highest temperature investigated. The HfCH₂-

Ph J _PCvalue (4 Hz) indicates that the PMe₃and benzyl

ligands are cis. These data are consistent with a C₁-

symmetric cis structure analogous to that for 25a ;

however, the η²-benzyl interaction is weaker in 26a than

in 25a and η²-η¹isomerization, which leads to equiva-

lencing of the sides of the Ph group via rotation around

the MCH₂-Ph bond in the η¹-benzyl intermediate, is

more rapid. The barrier calculated for exchange of the

sides of the benzyl phenyl group is ∆G^q(o-Ph exchange)

) 13.8(1) kcal/mol.⁵⁸Surprisingly, this barrier is higher

than that calculated for the same process in the

Exposure of a solution of 23a to 2 atm of ethylene at

23 °C (entry 6) results in a visibly exothermic reaction,

(58) Barriers for the exchange of the o-Ph hydrogens ∆G^q(o-Ph

exchange) and the m-Ph hydrogens ∆G^q(m-Ph exchange) were

calculated from the coalesence of the o-Ph resonances and of the m-Ph

resonances and are identical as expected. For o-Ph exchange: ∆υ(o-

Ph) ) 343 Hz, k_c) 761 s^-1, T_c) 303(2) K, ∆G^q(o-Ph exchange) )

13.8(1) kcal/mol. For m-Ph exchange: ∆υ(m-Ph) ) 455 Hz, k_c) 1010

s^-1, T_c) 308(2) K, ∆G^q(m-Ph exchange) ) 13.8(1) kcal/mol. The

apparent barrier for η²-η¹isomerization is calculated by assuming that

(57) For a review on early metal phosphine complexes, see: Fryzuk,

M. D.; Haddad, T. S.; Berg, D. J .; Rettig, S. J . Pure Appl. Chem. 1991,

63, 845.

) 2k(o-Ph exchange) is ∆G^q(η²-η¹) ) 13.3(1) kcal/mol.

)

²-η¹

k_(η

Group 4 Metal Alkyl Complexes

Organometallics, Vol. 16, No. 15, 1997 3297

immediate formation of solid polymer, and rapid (ca. 10

min) darkening of the reaction mixture from yellow to

brown. These observations suggest that polymerization

is initially rapid but that rapid catalyst deactivation also

occurs; the activity based on a 30 min polymerization

time is therefore a lower limit. The polymer produced

by 23a under these conditions is a linear, low molecular

weight polyethylene (0.3 branches/chain; M_n) 576) and

has a very narrow polydispersity (M_w/M_n) 1.18)

characteristic of a single site catalyst.⁵⁹NMR analysis

shows the presence of vinyl (50%) and saturated end

groups (50%), consistent with chain transfer via â-H

elimination, i.e., the polymer is a C₄₄R-olefin. It is

reasonable to propose that chain growth occurs on intact

(MeBr₂Ox)₂Zr(R)⁺cations; however, as yet there is no

direct evidence regarding this point.⁶⁰Catalyst deac-

tivation may occur via a variety of processes, including

migration of the growing alkyl chain or a hydride

(following â-H elimination) from Zr to a MeBr₂Ox^-

ligand, as observed for (MeBr₂Ox)₂Zr(CH₂Ph)₂.

for 23a , is observed. However, the polymer molecular

weight is much higher, ranging from M_w) 460 000

(light scattering) for the MAO cocatalyst to >2 000 000

for the [HNR₃][B(C₆F₅)₄] experiments. GPC measure-

ments were precluded by the low solubility of these

materials, so polydispersity data are not available. The

origin of this increase in molecular weight is unclear at

present, however, it is likely that MeBr₂Ox^-ligand

transfer to Al occurs in the catalyst generation process,

leading to complex chemistry.

Con clu sion s

New Zr(IV) and Hf(IV) alkyl complexes containing

substituted 8-quinolinolato ancillary ligands have been

prepared and structurally characterized by X-ray dif-

fraction and NMR spectroscopy. Neutral bis(hydrocar-

byl) complexes of general type (Ox)₂MR₂adopt C₂-

symmetric, distorted octahedral structures with a trans-

O, cis-N, cis-R ligand arrangement. Protonolysis of

these species with bulky ammonium reagents yields

base-free (Ox)₂M(R)⁺cations, which can be isolated as

the B(C₆F₅)₄^-salts. Cationic (MeBr₂Ox)₂M(η²-CH₂Ph)⁺

species 23a and 24a , which contain the electron-

withdrawing MeBr₂Ox^-ancillary ligand, adopt square

pyramidal structures in which the strongly distorted η²-

CH₂Ph group occupies the apical position and the basal

MeBr₂Ox^-ligands are arranged in a trans-O, trans-N

fashion. In contrast, distorted square pyramidal struc-

tures with an apical-O, cis-N ligand arrangement are

proposed for (MeOx)₂M(R)⁺cations 20a , 20b, and 22a .

The electronic properties of the Ox^-ligands and steric

interactions within the (Ox)₂M unit influence the struc-

tural preferences of these species. In particular, be-

cause both Ox^-oxygens must compete for π-donation

to the same metal acceptor orbital in the apical-R, trans-

O, trans-N square pyramidal structure observed for 23a

and 24a , this structure is disfavored for (MeOx)₂M(R)⁺

species which contain the stronger π-donor MeOx^-

ligand. Cations 23a and 24a form six-coordinate (MeBr₂-

Ox)₂M(η²-CH₂Ph)(L)⁺adducts with NMe₂Ph and PMe_3.

These species adopt structures analogous to those of

neutral (Ox)₂MR₂species, in which the benzyl and L

groups are cis and the trans-O, cis-N (Ox)₂M unit has

C₂symmetry. Thus, the (Ox)₂M unit undergoes signifi-

cant structural change upon conversion of six-coordinate

(Ox)₂M(R)₂or (Ox)₂M(R)(L)⁺species to five-coordinate

(Ox)₂M(R)⁺cations.

The neutral (Ox)₂MR₂complexes and the (Ox)₂MR⁺

cations are both chiral but undergo inversion of config-

uration at the metal center in solution, most likely by

M-N bond cleavage. Interestingly, the inversion bar-

riers are significantly higher for the five-coordinate

cations (>20 kcal/mol) than the six-coordinate neutral

species (15-18 kcal/mol), which may be explained by

the stronger M-N bond strength in the cations.

Several observations provide insight to Lewis acidity

trends in (Ox)₂MR₂and (Ox)₂M(R)⁺complexes. The

(MeBr₂Ox)₂M(η²-CH₂Ph)⁺cations 23a and 24a form

adducts with NMe₂Ph while the MeOx analogue 20a

does not, indicating that the electron-withdrawing Br

substituents increase the Lewis acidity at the metal

center as expected. Comparison of the MCH₂Ph J _HH

and J _CHvalues and η²-η¹isomerization barriers (∆G^q

(η²-η¹)) for (Ox)₂M(CH₂Ph)₂and (Ox)₂M(CH₂Ph)⁺com-

plexes (Table 4) indicates that the M‚‚‚Ph interactions

The activity of 23a is lower in chlorobenzene (entry

8) or toluene (entry 7) than in the mixed toluene/

chlorobenzene (1/1) solvent (entry 6). Visual observa-

tions (darkening of reaction mixture) suggest that

catalyst deactivation is faster in chlorobenzene which

may reduce the observed activity. Differences in ion

pairing in toluene versus chlorinated solvents are also

expected to influence activity.

The activity of the amine complex (MeBr₂Ox)₂Zr(CH₂-

Ph)(NMe₂Ph)⁺(21a ) (generated in situ by the reaction

of 11a with [HNMe₂Ph][B(C₆F₅)₄]; eq 10) is somewhat

lower than that of 23a (entry 3 vs 4), possibly as a result

of reversible coordination of NMe₂Ph. Similarly, (MeBr₂-

Ox)₂Hf(CH₂Ph)(NMe₂Ph)⁺is less active than 24a (entry

9 vs 10). Aluminum cocatalysts (added as scavengers)

have a significant effect on the ethylene polymerization

performance of 21a . The addition of Al(ⁱBu)₃(17 equiv

vs Zr) to 21a (entry 12) results in a significant increase

in the polymer molecular weight (M_n) 21 100) and

broadening of the molecular weight distribution (M_w/

M_n) 16.3). Similar results are obtained when (MeBr₂-

Ox)₂Zr(CH₂Ph)₂is activated by B(C₆F₅)₃in the presence

of Al(ⁱBu)₃(entry 13). The broad molecular weight

distributions indicate that these systems are multisite

catalysts. It is likely that the added AlR₃reagent

abstracts a MeBr₂Ox^-ligand from either 11a or 21a or

(MeBr₂Ox)₂Zr(R)⁺species (R ) growing chain), resulting

in complex secondary chemistry and generation of more

than one active catalyst. As noted above, MeBr₂Ox^-

transfer to Al is observed in the reactions of AlMe₃with

(MeBr₂Ox)₄Zr (13), (MeBr₂Ox)₂ZrCl₂(16), and (MeBr₂-

Ox)₂Zr(NMe₂)₂(17).

The activation of the dichloride complex (MeBr₂Ox)₂-

ZrCl₂(16) for ethylene polymerization was also briefly

investigated. Complex 16 is activated by methyl-

alumoxane (MAO, Al/Zr ) 680, run 14) or by treatment

with Al(ⁱBu)₃followed by [HNMe₂Ph][B(C₆F₅)₄] (run 15).

In each case, moderate activity, similar to that observed

(59) The M_w/M_nvalue may be decreased from the expected value of

2.0 by loss of some soluble low molecular weight material during

isolation of the polymer.

(60) Assuming that all (MeBr₂Ox)₂Zr(CH₂Ph)⁺centers are activated

and initially insert ethylene into the Zr-CH₂Ph bond, the catalyst

charge, polymer yield, and polymer M_nvalues imply that on average

1

each site produces 44 chains and, therefore, that

/₈₈of the chain ends

should be -CH₂Ph groups. This low concentration of end groups is

not detectable by NMR.

3298 Organometallics, Vol. 16, No. 15, 1997

Bei et al.

Ta ble 4. NMR Cou p lin g Con sta n ts (MCH₂P h ) a n d

F r ee En er gy Ba r r ier s for th e η²-η¹Ben zyl

Isom er iza tion of (Ox)₂M(CH₂P h )₂, (Ox)₂M(CH₂P h )⁺,

a n d (Ox)₂M(CH₂P h )(L)⁺Com p lexes

Ch a r t 6

∆G^q

J _HHJ _CH

(η²-η¹)

compound

(Hz) (Hz) (kcal/mol)

(MeOx)₂Zr(CH₂Ph)₂(9a )

8.5 129

10.2 120

9.6 132

11.3 125

8.8 130

10.9 122

8.8 145

10.0 143

9.1

(MeOx)₂Hf(CH₂Ph)₂(10a )

(MeOx)₂Zr(CH₂Ph)⁺(20a )

(MeOx)₂Hf(CH₂Ph)⁺(22a )

(MeBr₂Ox)₂Zr(CH₂Ph)₂(11a )

(MeBr₂Ox)₂Hf(CH₂Ph)₂(14a )

(MeBr₂Ox)₂Zr(CH₂Ph)⁺(23a )

(MeBr₂Ox)₂Hf(CH₂Ph)⁺(24a )

(MeBr₂Ox)₂Zr(CH₂Ph)(NMe₂Ph)⁺(21a )

(MeBr₂Ox)₂Hf(CH₂Ph)(NMe₂Ph)⁺

(MeBr₂Ox)₂Zr(CH₂Ph)(PMe₃)⁺(25a )

(MeBr₂Ox)₂Hf(CH₂Ph)(PMe₃)⁺(26a )

center and at the C2 and C4 carbons of the Ox ligands,

i.e., the electrophilicity is not concentrated at the metal

center as in a Cp₂M(R)⁺system. This presumably

reduces the electrophilicity of the metal site. Floriani

has noted a similar effect in group 4 metal (N₄-

macrocycle)MR₂and (N₄-macrocycle)MR⁺compounds.^4c

(iii) The presence of electrophilic sites (C2 and C4) and

nucleophilic sites (Ox^-oxygens) on the Ox^-ligands in

(Ox)₂MR₂and (Ox)₂MR⁺complexes leads to deleterious

reactions including thermal rearrangement via nucleo-

philic alkyl migration to C2 and Ox^-transfer to Al

reagents. (iv) Chiral (Ox)₂MR₂complexes undergo facile

inversion of configuration at the metal center. Studies

aimed at circumventing these problems by modification

of the Ox^-ligands are in progress.

Finally, it may be noted that the (Ox)₂MR₂and

(Ox)₂M(R)⁺systems studied here bear a topological

resemblance to the chiral, octahedral Ti active sites

which have been proposed for supported Ziegler-Natta

catalysts (Chart 6).⁶³Efforts are underway to develop

more reactive and stereorigid, octahedral, and five-

coordinate (LL)₂MR₂and (LL)₂MR⁺species based on

bidentate ancillary ligands (LL), which may be of use

for modeling the properties and reactivity of such sites

and for catalytic applications.

14.0(1)

11.4(2)

11.3

7.5 145

9

141

are stronger and the benzyl ligands are more distorted

in the Zr species than in the corresponding Hf species.

This trend suggests that the Zr complexes are stronger

Lewis acids than the corresponding Hf complexes.

While few quantitative data are available, the relative

Lewis acidity of ZrX₄and HfX₄complexes varies de-

pending on the nature of the X groups and the Lewis

base.⁶¹

The ethylene polymerization behavior of (Ox)₂MR⁺

species is strongly influenced by the ligand properties

and the identity of the metal. The (MeBr₂Ox)₂M(η²-

CH₂Ph)⁺cations 23a and 24a exhibit moderate ethylene

polymerization activity, while the MeOx analogues

(MeOx)₂Zr(CH₂Ph)⁺(20a ) and (MeOx)₂Zr(CH₂CMe₃)⁺

(20b) are inactive, at least under the conditions studied.

The enhancement in activity due to incorporation of the

electron-withdrawing bromine substituents in 23a and

24a may result from the increased metal Lewis acidity,

from structural effects (ligand arrangement in square

pyramidal (Ox)₂MR⁺structures), or other factors. Nei-

ther 20a nor 20b coordinate NMe₂Ph, so these species

are probably not electrophilic enough to coordinate and

activate ethylene. In contrast, electron-donating sub-

stituents generally increase the olefin polymerization

activity of metallocene catalysts.⁶²

This work shows that the general catalyst design

principles developed for metallocene systems can be

extended to (Ox)₂MR₂/(Ox)₂MR⁺systems and that elec-

tron-withdrawing MeBr₂Ox^-ligands are preferable to

MeOx^-ligands for olefin polymerization activity. How-

ever, the (Ox)₂MR⁺systems differ from Cp₂MR⁺systems

in several respects, which has a deleterious effect on

catalyst performance. (i) The (Ox)₂M unit undergoes

significant structural change when a (Ox)₂MR₂species

is converted to a (Ox)₂MR⁺cation. This structural

relaxation presumably stabilizes and reduces the elec-

trophilicity of the cation and disfavors coordination of

an olefin or other Lewis base. In contrast, the Cp₂M

structure is not significantly perturbed when a Cp₂MR₂

species is ionized to an active Cp₂MR⁺cation.¹(ii) The

(Ox)₂MR⁺cations contain electrophilic sites at the metal

Exp er im en ta l Section

Gen er a l Con sid er a tion s. All experiments were per-

formed under nitrogen or vacuum using a glovebox or a high-

vacuum line. Benzene, toluene, pentane, hexanes, ether,

and THF were dried by distillation over Na/benzophenone.

Methylene chloride and chlorobenzene were distilled over

CaH₂. Benzene-d₆, THF-d₈, and toluene-d₈were dried over

Na, and methylene chloride-d₂and chlorobenzene-d₅were

dried over P₂O₅. NMR spectra were obtained on Bruker AMX-

360 (¹H, ¹³C, ¹¹B) or AC-300 (¹⁹F) instruments at ambient probe

temperature (25 °C), unless indicated otherwise. J _CHvalues

were obtained from gated {¹H}¹³C NMR spectra. ¹H NMR

assignments for (Ox)₂MR₂and (Ox)₂MR⁺complexes were made

by analogy to the assignments for MeOxH and MeBr₂OxH^64,65

and were confirmed by homonuclear decoupling experiments

for 10a , 20a ,b, and 22a and COSY and NOESY experiments

for 19, 22a , and 25a . NMR assignments are reported using

the numbering scheme in Chart 1. For 20a , 20b, and 22a ,

the entries Hx′ and Me′ and Hx and Me denote the hydrogens

in the MeOx′ and MeOx ligands, respectively; see Chart 3.

(63) See: Corradini, P.; Busico, V.; Cavallo, L.; Guerra, G.; Vacatello,

M.; Venditto, V. J . Mol. Catal. 1992, 74, 433 and references therein.

(64) (a) ¹H NMR data for MeOxH (C₆D₆): δ 8.68 (s, 1H, OH), 7.42

(d, J ) 8.4 Hz, 1H, H4), 7.16 (dd, J ) 7.6, 1.3 Hz, 1H, H5), 7.11 (t, J

) 8.0, 1H, H6), 6.96 (dd, J ) 8.1, 1.3 Hz, 1H, H7), 6.63 (d, J ) 8.4 Hz,

1H, H3), 2.29 (s, 3H, Me). NOESY results confirm the assignments of

H5 and H7. ¹H NMR data for MeBr₂OxH (C₆D₆): δ 8.60 (s, 1H, OH),

7.81 (d, J ) 8.6 Hz, 1H, H4), 7.60 (s, 1H, H6), 6.51 (d, J ) 8.6 Hz, 1H,

H3), 2.12 (s, 3H, Me).

(61) (a) Felten, J . J .; Anderson, W. P. J . Organomet. Chem. 1974,

82, 375. (b) Felten, J . J .; Anderson, W. P. J . Organomet. Chem. 1972,

36, 87. (c) Chung, F. M.; Westland, A. D. Can. J . Chem. 1969, 47, 195.

(d) Krzhizhanovskaya, E. E; Suvarov, A. V. Zh. Neorg. Khim. 1971,

16, 3380. (e) Hummers, W. S.; Tyree, S. Y., J r.; Yolles, S. J . Am. Chem.

Soc. 1952, 74, 139.

(62) See discussion in ref 1g and (a) Lee, I.; Gauthier, W. J .; Ball, J .

A.; Iyengar, B.; Collins, S. Organometallics 1992, 11, 2115 and

references therein.

(65) For NMR studies of 8-quinolinols and 8-quinolinolato com-

plexes, see: (a) Baker, H. C.; Sawyer, D. T. Anal. Chem. 1968, 40, 1945.

(b) Hanrahan, E. S.; Chakrabarty, M. R. J . Magn. Reson. 1970, 2, 19.

Group 4 Metal Alkyl Complexes

Organometallics, Vol. 16, No. 15, 1997 3299

Coupling constants are reported in Hertz. Elemental analyses

were performed by E & R Microanalytical Laboratory, Inc. The

following compounds were prepared by literature methods:

MR₄(M ) Zr, R ) CH₂Ph, CH₂CMe₃, CH₂SiMe₃; M ) Hf, R )

CH₂Ph),⁶⁶[HNMe₂Ph][B(C₆F₅)₄], [HNMePh₂][B(C₆F₅)₄].^6a

MeOxH and MeBr₂OxH were obtained from Aldrich and used

without purification.

(MeOx)Li (2-Li). A solution of BuLi (32 mmol) in pentane/

hexanes (20 mL) was added to a slurry of MeOxH (5.17 g, 32.5

mmol) in pentane (30 mL) at room temperature. An off-white

precipitate appeared. The reaction mixture was stirred for 10

min and filtered, yielding an off-white solid (4.80 g, 90.8%).

The identity of 2-Li was confirmed by hydrolysis to MeOxH

and by reaction with ZrCl₄to yield (MeOx)₂ZrCl₂. ¹H NMR

(THF-d₈): δ 7.91 (1H, br), 7.09 (2H, br), 6.71 (2H, br), 2.47

(3H, br, Me).

(MeBr ₂Ox)Li (3-Li). A solution of BuLi (27.5 mmol) in

toluene (40 mL) was added to a toluene solution (50 mL) of

MeBr₂OxH (9.21 g, 29.1 mmol) over 5 min at room tempera-

ture. The reaction mixture was stirred for 10 min after the

addition and filtered, affording a yellow solid (8.99 g, 96%).

¹H NMR (THF-d₈): δ 8.26 (d, J ) 8.6, 1H, H4), 7.75 (s, 1H,

H6), 7.36 (d, J ) 8.6, 1H, H3), 2.63 (s, 3H, Me).

(MeOx)₂Zr (CH₂P h )₂(9a ). A toluene solution (20 mL) of

MeOxH (0.714 g, 4.49 mmol) was added to a toluene solution

(100 mL) of Zr(CH₂Ph)₄(1.02 g, 2.25 mmol) dropwise at room

temperature over 20 min. The reaction flask was shielded

from room light by Al foil. The color of the reaction mixture

changed from yellow to orange. After an additional 20 min of

stirring, the orange solution was concentrated under vacuum

until an orange solid appeared (ca. 10 mL of solution left). The

mixture was cooled to -40 °C for 24 h and filtered, which

afforded an orange solid (1.09 g, 82.3%). Crystals suitable for

X-ray crystallography were obtained by recrystallization from

toluene/pentane. Anal. Calcd for C₃₄H₃₀N₂O₂Zr: C, 69.23; H,

5.13; N, 4.75. Found: C, 69.06; H, 4.99; N, 5.00. ¹H NMR

(C₆D₆): δ 7.25 (d, J ) 8.3, 2H, H4), 7.24 (t, J ) 7.8, 2H, H6),

7.11 (d, J ) 7.5, 2H, H5), 6.91 (d, J ) 7.6, 4H, o-Ph), 6.8 (m,

6H, H7 and m-Ph), 6.62 (t, J ) 7.1, 2H, p-Ph), 6.16 (d, J )

8.3, 2H, H3), 2.65 (d, J ) 8.5, 2H, ZrCH₂), 2.38 (d, J ) 8.5,

2H, ZrCH₂), 1.95 (s, 6H, Me). ¹³C NMR (C₆D₆): δ 161.0, 159.1,

144.3 (ipso-Ph), 143.6, 138.2, 128.9, 128.9, 128.7, 127.9, 123.8,

122.1, 115.9, 114.3, 64.0 (J _CH) 129 Hz, ZrCH₂), 23.2.

(MeOx)₂Zr (CH₂CMe₃)₂(9b). A benzene solution (10 mL)

of MeOxH (0.233 g, 1.54 mmol) was added to a pentane

solution (30 mL) of Zr(CH₂CMe₃)₄(0.292 g, 0.777 mmol)

dropwise over 25 min at room temperature. The bright yellow

reaction mixture was stirred for 1 h after the addition, and

the solvent was removed under vacuum, yielding 0.390 g

(94.8%) of a yellow solid. This product is sufficiently pure for

further reactions. The product was recrystallized from toluene/

pentane at -40 °C (38.7%). Anal. Calcd for C₃₀H₃₈N₂O₂Zr:

C, 65.53; H, 6.97; N, 5.10. Found: C, 65.68; H, 6.78; N, 5.32.

¹H NMR (C₆D₆): δ 7.24 (m, AB part of ABX, 4H, H5 and H6),

7.12 (d, J ) 8.4, 2H, H4), 6.78 (m, X part of ABX, 2H, H7),

6.14 (d, J ) 8.4, 2H, H3), 2.5 (s, 6H, MeOx), 2.10 (br d, 2H,

ZrCH₂), 1.72 (br d, 2H, ZrCH₂), 1.23 (s, 18H, CMe₃). ¹³C NMR

(C₆D₆): δ 161.2, 159.4, 143.1, 138.3, 128.7, 128.0, 123.5, 116.5,

114.1, 87.3 (ZrCH₂, J _CH) 105), 35.4, 34.7, 23.5.

part of ABX, 2H, H7), 6.15 (d, J ) 8.4, 2H, H3), 2.55 (s, 6H,

MeOx), 1.26 (br d, 4H, ZrCH₂), 0.18 (s, 18H, SiMe₃). ¹³C NMR

(C₆D₆): 161.0, 159.6, 143.0, 138.5, 128.7, 128.0, 123.6, 116.5,

114.1, 57.9 (ZrCH₂, J _CH) 103), 23.5, 2.8.

(MeOx)₂Hf(CH₂P h )₂(10a ). A toluene solution (20 mL) of

MeOxH (0.601 g, 3.98 mmol) was added to a toluene solution

(60 mL) of Hf(CH₂Ph)₄(1.09 g, 2.01 mmol) dropwise over 20

min. The reaction mixture was stirred for 5 min and concen-

trated under vacuum until a yellow solid appeared (ca. 5 mL

of solution left). The mixture was cooled to -40 °C for 24 h

and filtered, yielding a yellow solid (1.30 g, 98.5%). ¹H NMR

(C₆D₆): δ 7.27 (t, J ) 7.8, 2H, H6), 7.19 (m, 4H, H4 and H5),

6.90 (d, J ) 7.7, 4H, o-Ph), 6.76 (m, 6H, H7 and m-Ph), 6.48

(t, J ) 7.2, 2H, p-Ph), 6.10 (d, J ) 8.3, 2H, H3), 2.79 (s, 4H,

HfCH₂), 1.98 (s, 6H, Me). ¹³C NMR (C₆D₆): δ 161.0, 159.8,

146.3 (ipso-Ph), 143.4, 138.6, 129.0, 127.9, 127.7, 127.6, 123.7,

121.0, 116.1, 115.4, 73.9 (J _CH) 120, HfCH₂), 23.0.

(MeBr ₂Ox)₂Zr (CH₂P h )₂(11a ). A toluene solution (60 mL)

of MeBr₂OxH (1.88 g, 5.94 mmol) was added to a toluene

solution (200 mL) of Zr(CH₂Ph)₄(1.38 g, 3.03 mmol) dropwise

over 40 min at room temperature. The reaction flask was

shielded from room light with Al foil. The deep orange solution

was concentrated under vacuum to 15 mL, cooled to -40 °C

for 24 h, and filtered, yielding an orange solid (2.13 g, 79.4%).

Anal. Calcd for C₃₄H₂₆Br₄N₂O₂Zr: C, 45.10; H, 2.89; N, 3.09.

Found: C, 44.99; H, 3.00; N, 3.12. ¹H NMR (CD₂Cl₂): δ 8.29

(d, J ) 8.6, 2H, H4), 7.93 (s, 2H, H6), 7.13 (d, J ) 8.6, 2H,

H3), 6.80 (t, J ) 7.4, 4H, m-Ph), 6.64 (t, J ) 7.4, 2H, p-Ph),

6.57 (d, J ) 7.5, 4H, o-Ph), 2.05 (d, J ) 8.7, 2H, ZrCH₂), 1.99

(s, 6H, Me), 1.86 (d, J ) 8.8, 2H, ZrCH₂). ¹³C NMR (CD₂Cl₂):

161.2, 157.2, 143.2, 142.9, 138.7, 134.5, 129.0, 128.8, 126.2,

125.4, 122.5, 108.4 (C5 or C7), 108.2 (C7 or C5), 64.8 (J ) 130,

ZrCH₂), 23.1.

(MeBr ₂Ox)₂Zr (CH₂CMe₃)₂(11b). A slurry of MeBr₂OxH

(0.872 g, 2.75 mmol) in hexane (25 mL) was added to a hexane

solution (50 mL) of Zr(CH₂CMe₃)₄(0.517 g, 1.38 mmol) drop-

wise over 20 min. The volatiles were removed under vacuum,

and the residue was washed with hexanes, yielding a yellow

1

solid (0.888 g, 74.0%). The H NMR spectrum indicated that

this product was >95% pure 11b. This sample was used for

the dynamic NMR study without further purification. ¹H

NMR (C₆D₆): δ 7.81 (s, 2H, H6), 7.61 (d, J ) 8.6, 2H, H4),

6.02 (d, J ) 8.6, 2H, H3), 2.34 (s, 6H, MeBr₂Ox), 2.08 (d, J )

13, 2H, ZrCH₂), 1.64 (d, J ) 13, 2H, ZrCH₂), 1.26 (s, 18H,

CMe₃). ¹³C NMR (C₆D₆): δ 161.1, 157.7, 142.8, 138.0, 134.5,

124.5, 108.8, 108.7, 91.0 35.5, 34.7, 23.2.

(MeBr ₂Ox)₄Zr (13). A toluene solution (15 mL) of Zr(CH₂-

Ph)₄(0.540 g, 1.18 mmol) was added to a toluene solution (80

mL) of MeBr₂OxH (1.51 g, 4.76 mmol) at room temperature.

The reaction mixture was stirred for 10 min, concentrated to

15 mL under vacuum, and cooled to -40 °C for 12 h. The

yellow solid (1.33 g, 83.2%) was collected by filtration and dried

under vacuum. ¹H NMR (C₆D₆): δ 7.69 (s, 4H, H6), 7.42 (d, J

) 8.6, 4H, H4), 6.26 (d, J ) 8.6, 4H, H3), 3.54 (s, 12H, Me).

¹³C NMR (C₆D₆): δ 161.8, 158.2, 143.2, 136.6, 133.7, 125.9,

125.2, 107.2, 106.9, 24.9.

(MeBr ₂Ox)₂Hf(CH₂P h )₂(14a ). A toluene solution (50 mL)

of MeBr₂OxH (1.17 g, 3.69 mmol) was added to a toluene

solution (150 mL) of Hf(CH₂Ph)₄(1.00 g, 1.85 mmol) dropwise

over 35 min at room temperature. The orange solution was

concentrated to 10 mL under vacuum and cooled to -40 °C

for 12 h. The orange solid was isolated by filtration (1.28 g,

75%). Anal. Calcd for C₃₄H₂₆Br₄N₂O₂Hf: C, 41.13; H, 2.64;

N, 2.82. Found: C, 41.13; H, 2.70; N, 2.72. ¹H NMR (C₆D₆):

δ 7.85 (s, 2H, H6), 7.75 (d, J ) 8.6, 2H, H4), 6.88 (d, J ) 7.3,

4H, o-Ph), 6.73 (t, J ) 7.6, 4H, m-Ph), 6.46 (t, J ) 7.3, 2H,

p-Ph), 6.04 (d, J ) 8.7, 2H, H3), 2.72 (d, J ) 10.9, 2H, HfCH₂),

2.63 (d, J ) 10.6, 2H, HfCH₂), 1.73 (s, 6H, Me). ¹³C NMR

(C₆D₆): δ 161.5, 157.9, 144.6 (ipso-Ph), 143.2, 138.4, 134.9,

128.3, 128.0, 126.1, 125.0, 121.9, 110.0, 108.5, 75.3 (J _CH) 122,

HfCH₂), 22.7.

(MeOx)₂Zr (CH₂SiMe₃)₂(9c). A benzene solution (15 mL)

of MeOxH (0.210 g, 1.39 mmol) was added to a pentane

solution (30 mL) of Zr(CH₂SiMe₃)₄(0.319 g, 0.71 mmol)

dropwise over 25 min at room temperature. The yellow-brown

reaction mixture was stirred for 1 h after the addition. The

solvent was removed under vacuum, yielding a brown solid

(0.382 g, 95%). This compound could not be recrystallized due

to its high solubility. ¹H NMR (C₆D₆): δ 7.21 (m, AB part of

ABX, 4H, H5 and H6), 7.11 (d, J ) 8.3, 2H, H4), 6.76 (m, X

(66) (a) Zucchini, U.; Albizzati, E.; Giannini, U. J . Organomet. Chem.

1971, 26, 357. (b) Davidson, P. J .; Lappert, M. F.; Pearce, R. J .

Organomet. Chem. 1973, 57, 269.

3300 Organometallics, Vol. 16, No. 15, 1997

Bei et al.

(MeOx)₂Zr Cl₂(15). Ether (50 mL) was added to a solid

mixture of ZrCl₄(2.50 g, 10.7 mmol) and (MeOx)Li (2-Li) (3.60

g, 20.2 mmol) at room temperature. The reaction mixture was

stirred for 2 days and the solvent was removed under vacuum,

1.5 h at 60 °C. The volatiles were removed under vacuum,

leaving a brown sticky residue, which was extracted with a

mixture of benzene and pentane (40 mL, ca. 3/2 by volume).

The extract was evaporated to dryness under vacuum, yielding

1

yielding a yellow solid. The H NMR spectrum indicated that

a brown solid (0.419 g, 44.1%; ca. 90% 19 and 10% 11a by H

this material contained 15 as the major MeOx product (ca.

90%). ¹H NMR (CD₂Cl₂): δ 8.05 (d, J ) 8.3, 2H, H4), 7.45 (t,

J ) 7.8, 2H, H6), 7.23 (dd, J ) 8.2, 1.1, 2H, H5), 7.20 (d, J )

8.5, 2H, H3), 7.05 (dd, J ) 7.6, 1.1, 2H, H7), 3.06 (s, 6H, Me).

This material was used directly without isolation from LiCl

due to its low solubility. The identity of 15 was confirmed by

an alternate synthesis. A toluene solution (15 mL) of MeOxH

(0.152 g, 1.01 mmol) was added to a toluene solution (25 mL)

of Zr(CH₂Ph)₄(0.232 g, 0.509 mmol) dropwise over 10 min.

The solution was stirred for 10 min, and solid [HNMe₃]Cl

(0.095 g, 0.994 mmol) was added. The mixture was stirred

for 12 h, cooled to -40 °C for 12 h, and filtered, yielding a

yellow solid (0.175 g, 76.1%). The ¹H NMR spectrum of this

material was identical to that prepared from (MeOx)Li and

ZrCl₄.

(MeBr ₂Ox)₂Zr Cl₂(16). Ether (80 mL) was added to a solid

mixture of (MeBr₂Ox)Li (3-Li) (2.96 g, 9.15 mmol) and ZrCl₄

(1.05 g, 4.49 mmol). The reaction mixture was stirred for 2

days at room temperature, and the solvent was removed under

vacuum, yielding a yellow solid. The ¹H NMR spectrum

indicated that this material contained 16 as the major MeBr₂-

Ox containing product (>90%). This material was used

directly without further purification due to its low solubility.

An analytically pure sample of 16 was obtained by the

following route. Methylene chloride (20 mL) was added to a

solid mixture of (MeBr₂Ox)₂Zr(CH₂Ph)₂(0.523 g, 0.578 mmol)

and [HNMe₃]Cl (0.092 g, 0.96 mmol) at room temperature. The

reaction mixture was stirred for 30 min and concentrated

under vacuum to 10 mL, and benzene (10 mL) was added. The

yellow solid (0.312 g, 70%) was collected by filtration and dried

under vacuum. Anal. Calcd for C₂₀H₁₂Br₄Cl₂N₂O₂Zr: C, 30.24;

H, 1.52; N, 3.53; Cl, 8.93. Found: C, 30.08; H, 1.44; N, 3.41;

Cl, 9.10. ¹H NMR (CD₂Cl₂): δ 8.35 (d, J ) 8.6, 2H, H4), 7.95

(s, 2H, H6), 7.36 (d, J ) 8.6, 2H, H3), 3.11 (s, 6H, Me).

(MeBr ₂Ox)₂Zr (NMe₂)₂(17). An ether slurry (80 mL) of

(MeBr₂Ox)₂ZrCl₂(16, 2.33 mmol) was generated by the reac-

tion of ZrCl₄(0.540 g, 2.33 mmol) and (MeBr₂Ox)Li (3-Li, 1.50

g, 4.66 mmol) as described above. Solid LiNMe₂(0.256 g, 5.02

mmol) was added at room temperature. The brown reaction

mixture was stirred for 5 h at room temperature, and the

solvent was removed under vacuum. The residue was taken

up in benzene (80 mL) and filtered. The solvent was removed

from the filtrate under vacuum, yielding a tan solid (1.54 g,

81.5%). Anal. Calcd for C₂₄H₂₄Br₄N₄O₂Zr: C, 35.53; H, 2.98;

N, 6.90. Found, C, 35.11; H, 2.79; N, 4.90 (duplicate analysis

also gave a low %N value, 5.6%). ¹H NMR (C₆D₆): δ 7.82 (s,

2H, H6), 7.61 (d, J ) 8.6, 2H, H4), 6.13 (d, J ) 8.6, 2H, H3),

3.30 (s, 12H, NMe₂), 2.52 (s, 6H, MeBr₂Ox). ¹³C NMR (C₆D₆):

δ 161.0, 157.9, 143.1, 137.7, 134.4, 126.2, 124.5, 108.5, 107.1,

44.0, 23.5.

NMR). A portion (0.267 g) of this material was dissolved in

toluene (5 mL), and the solution was layered with hexane (20

mL) and cooled to -40 °C for 24 h. The yellow solid which

formed was collected by filtration and dried under vacuum

(0.123 g, 46.1% recrystallization yield). The ¹H NMR spectrum

established that this material contains 1 equiv of toluene vs

19. Anal. Calcd for C₃₄H₂₆Br₄N₄O₂Zr‚C₇H₈: C, 49.36; H, 3.44;

N, 2.81. Found: C, 47.33; H, 3.24; N, 3.22 (the low %C values

may be due to toluene loss during analysis). ¹H NMR (CD₂-

Cl₂): δ 8.37 (d, J ) 8.7, 1H, H4), 7.99 (s, 1H, H6 or H6′), 7.50

(s, 1H, H6′ or H6), 7.15 (d, J ) 8.9, 1H, H3), 7.05 (m, 3H, p-Ph′

and m-Ph′), 6.83 (d, J ) 6.6, 2H, o-Ph′), 6.74 (d, J ) 9.8, 1H,

H4′), 6.69 (t, J ) 7.7, 2H, m-Ph), 6.57 (t, J ) 6.9, 1H, p-Ph),

6.29 (d, J ) 7.2, 2H, o-Ph), 4.99 (d, J ) 9.4, 1H, H3′), 3.31 (d,

J ) 12.2, 1H, CH₂Ph′), 2.86 (d, J ) 11.8, 1H, CH₂Ph), 2.84 (d,

J ) 11.8, 1H, CH₂Ph), 2.32 (d, J ) 13, 1H, CH₂Ph′), 2.07 (s,

3H, MeBr₂Ox), 0.62 (s, 3H, MeBr₂Ox′). ¹³C NMR (CD₂Cl₂): δ

163.0, 156.3, 149.5, 145.3, 142.1, 139.5, 138.2, 136.4, 135.2,

134.9, 131.7, 127.7, 127.6, 126.5, 126.4, 126.3, 126.1, 125.6,

125.5, 123.9, 121.6, 115.8, 113.5, 110.0, 109.0, 73.6 (CH₂Ph,

J _CH) 116), 61.5 (C2′), 48.3 (CH₂Ph′, J _CH) 126), 25.2, 25.1;

one ipso C resonance not observed.

[(MeOx)₂Zr (CH₂P h )][B(C₆F ₅)₄] (20a ). A mixture of (Me-

Ox)₂Zr(CH₂Ph)₂(9a , 0.298 g, 0.517 mmol) and [HNMePh₂]-

[B(C₆F₅)₄] (0.438 g, 0.507 mmol) in benzene (5 mL) was stirred

at room temperature for 5 min. A brown oil separated. The

supernatant was decanted from the oil. The oil was washed

with benzene (5 mL) and dried under vacuum, yielding a

brown solid (0.442 g, 75.1%). ¹H NMR (CD₂Cl₂): δ 8.42 (d, J

) 8.4, 1H, H4), 8.41 (d, J ) 7.5, 1H, H7), 8.32 (d, J ) 8.4, 1H,

H4′), 7.87 (t, J ) 7.8, 1H, H6), 7.80 (d, J ) 7.1, 1H, H5), 7.71

(t, J ) 8.1, 1H, H6′), 7.53 (m, 2H, H5′, H7′), 7.32 (d, J ) 8.3,

1H, H3), 7.00 (t, J ) 7.7, 2H, m-Ph), 6.93 (d, J ) 6.8, 2H, o-Ph),

6.82 (d, J ) 8.3, 1H, H3′), 6.72 (t, J ) 6.8, 1H, p-Ph), 3.64 (d,

J ) 9.5, 1H, ZrCH₂), 3.29 (d, J ) 9.7, 1H, ZrCH₂), 1.95 (s, 3H,

Me), 0.56 (s, 3H, Me′). ¹³C NMR (CD₂Cl₂): δ 160.8, 160.5,

155.1, 151.8, 148.6 (d, J _CF) 241, B(C₆F₅)₄^-), 143.3, 143.2,

143.0, 139.5, 138.6 (d, J _CF) 243, B(C₆F₅)₄^-), 137.2, 136.7 (d,

J _CF) 243, B(C₆F₅)₄^-), 132.0, 130.3, 130.2, 129.2, 128.8, 128.5,

127.9, 125.8, 124.9, 124.8, 124.0 (br, B(C₆F₅)₄^-), 121.9, 120.2,

116.3, 82.0 (J _CH) 132, ZrCH₂), 24.1, 22.7.

[(MeOx)₂Zr (CH₂CMe₃)][B(C₆F ₅)₄] (20b). A mixture of

(MeOx)₂Zr(CH₂CMe₃)₂(9b, 0.105 g, 0.197 mmol) and [HNMePh₂]-

[B(C₆F₅)₄] (0.163 g, 0.189 mmol) in benzene was stirred for 15

min at room temperature. A brown oil separated. The

supernatant was removed by pipette, and the residue was

washed with benzene (2 mL) and dried under vacuum, yielding

a yellow solid (0.205 g, 87.4%). ¹H NMR (CD₂Cl₂): δ 8.77 (d,

J ) 7.6, 1H, H7), 8.65 (d, J ) 8.5 Hz, 1H, H4), 8.31 (d, J )

8.3, 1H, H4′), 8.04 (t, J ) 8.0, 1H, H6), 7.97 (d, J ) 7.7, 1H,

H5), 7.72 (t, J ) 7.9, 1H, H6′), 7.60 (m, 3H, H3, H5′, H7′),

6.74 (d, J ) 8.3, 1H, H3′), 2.62 (d, J ) 11.3, 1H, ZrCH₂), 2.60

(s, 3H, MeOx), 2.40 (d, J ) 11.4, 1H, ZrCH₂), 0.76 (s, 9H,

CMe₃), 0.46 (s, 3H, MeOx′). ¹³C NMR (CD₂Cl₂): δ 160.9, 160.3,

154.7, 151.7, 148.5 (d, J _CF) 241, B(C₆F₅)₄^-), 144.7, 143.1,

Gen er a tion of (MeBr ₂Ox)AlMe₂(18). A hexane slurry

(20 mL) of MeBr₂OxH (1.59 g, 5.03 mmol) was added to a

hexane solution (3 mL) of AlMe₃(6 mmol) at room tempera-

ture. A yellow precipitate formed. The mixture was stirred

for 20 min and filtered, yielding a yellow solid (1.41 g, 74.9%).

The ¹H NMR spectrum indicated that this material contains

87% (MeBr₂Ox)AlMe₂and 13% (MeBr₂Ox)₂AlMe.^{67 1}H NMR

(CD₂Cl₂): δ 8.53 (d, J ) 8.6, 1H, H4), 7.91 (s, 1H, H6), 7.55 (d,

J ) 8.6, 1H, H3), 2.86 (s, 3H, MeBr₂Ox), -0.58 (s, 6H, AlMe₂).

¹³C NMR (CD₂Cl₂): δ 159.5, 158.2, 141.0, 139.7, 135.7, 129.3,

124.8, 109.7, 105.2, 23.1, -10.5 (br, AlMe, J _CH) 104).

Th er m a l Rea r r a n gem en t of 11a to 19. A toluene solu-

tion (80 mL) of (MeBrOx)₂Zr(CH₂Ph)₂(0.950 g) was stirred for

143.0, 138.6 (d, J _CF) 243, B(C₆F₅)₄^-), 136.7, 136.6 (d, J _CF

)

243, B(C₆F₅)₄^-), 130.7, 130.4, 128.6, 125.7, 125.4, 125.0, 124.0

(br, B(C₆F₅)₄^-), 122.1, 119.9, 118.1 (J _CH) 100, ZrCH₂), 116.7,

39.4, 32.5, 24.3, 22.2; one aromatic carbon was not observed.

[(MeBr ₂Ox)₂Zr (CH₂P h )(NMe₂P h )][B(C₆F ₅)₄] (21a ). An

NMR tube was charged with (MeBr₂Ox)₂Zr(CH₂Ph)₂(11a , 14.9

mg, 0.016 mmol) and [HNMe₂Ph][B(C₆F₅)₄] (12.1 mg, 0.015

mmol), and CD₂Cl₂(0.5 mL) was added by vacuum transfer

at -78 °C. The NMR tube was maintained at -78 °C. A clear

1

yellow solution formed within 5 min. The H NMR spectrum

(67) ¹H NMR data for (MeBr₂Ox)₂AlMe (CD₂Cl₂): δ 8.44 (d, J ) 8.6

Hz, 2H, H4), 7.84 (s, 2H, H6), 7.60 (d, J ) 8.7 Hz, 2H, H3), 3.19 (s,

6H, Me), -0.66 (s, 3H, AlMe).

was recorded at -40 °C and indicated that 21a was formed

quantitatively. ¹H NMR (CD₂Cl₂, -40 °C): δ 8.43 (d, J ) 8.6,

Group 4 Metal Alkyl Complexes

Organometallics, Vol. 16, No. 15, 1997 3301

1H, H4), 8.36 (d, J ) 8.6, 1H, H4), 8.09 (s, 1H, H6), 8.08 (s,

1H, H6), 7.4-6.7 (m, 12H, H3 and Ph), 3.46 (s, 3H, NMe₂Ph),

3.16 (d, J ) 9.1, 1H, ZrCH₂), 3.10 (d, J ) 9.1, 1H, ZrCH₂),

3.00 (s, 3H, NMe₂Ph), 1.64 (s, 3H, MeBr₂Ox), 1.36 (s, 3H,

MeBr₂Ox). The room-temperature H NMR spectrum of this

compound contains broad resonances characteristic of NMe₂-

Ph exchange, as described in the text.

77.7 (J _CH) 145, ZrCH₂), 26.1; two aromatic carbons were not

observed. ¹¹B NMR (CD₂Cl₂): δ -15.2. ¹⁹F NMR (CD₂Cl₂, -50

°C): δ -133.4 (8F), -162.5 (4F), -166.6 (8F).

[(MeBr ₂Ox)₂Hf(CH₂P h )][B(C₆F ₅)₄] (24a ). Benzene (3 mL)

was added to a solid mixture of (MeBr₂Ox)₂Hf(CH₂Ph)₂(14a ,

0.302 g, 0.304 mmol) and [HNMePh₂][B(C₆F₅)₄] (0.261 g, 0.302

mmol) at room temperature. The reaction mixture was stirred

for 10 min, and a brown oil separated. The supernatant was

removed by pipette, and the oil was washed with benzene (3

mL) and dried under vacuum, yielding a yellow solid (0.276 g,

92.1%). The ¹H NMR spectrum indicated that this material

1

[(MeBr ₂Ox)₂Hf(CH₂P h )(NMe₂P h )][B(C₆F ₅)₄]. An NMR

tube was charged with (MeBr₂Ox)₂Zr(CH₂Ph)₂(14a , 22.6 mg,

0.0228 mmol) and [HNMe₂Ph][B(C₆F₅)₄] (19.5 mg, 0.0243

mmol), and CD₂Cl₂(0.5 mL) was added by vacuum transfer

to yield a yellow solution. The ¹H NMR spectrum was recorded

at -40 °C and established that the formation of (MeBr₂Ox)₂Hf-

(CH₂Ph)(NMe₂Ph)⁺was quantitative. ¹H NMR (CD₂Cl₂, -40

°C): δ 8.46 (d, J ) 8.6, 1H, H4), 8.38 (d, J ) 8.5, 1H, H4), 8.12

(s, 1H, H6), 8.10 (s, 1H, H6), 7.8-6.2 (m, 12H, H3 and Ph),

3.92 (s, 3H, NMe₂Ph), 3.78 (s, 3H, NMe₂Ph), 2.73 (d, J ) 11.3,

1H, HfCH₂), 2.43 (d, J ) 11.3, 1H, HfCH₂), 1.60 (s, 3H, MeBr₂-

contained 1.2 equiv of occluded benzene. Anal. Calcd for C₅₁

-

H

₁₉BBr₄F₂₀N₂O₂Hf‚1.2C₆H₆: C, 41.75; H, 1.58; N, 1.67.

Found: C, 41.67; H, 1.81; N, 1.67. ¹H NMR (CD₂Cl₂): δ 8.73

(d, J ) 8.6, 2H, H4), 8.09 (s, 2H, H6), 7.76 (d, J ) 8.7, 2H,

H3), 7.19 (br s, 2H, m-Ph), 6.98 (d, J ) 7.2, 2H, o-Ph), 6.79 (t,

J ) 7.5, 1H, p-Ph), 3.22 (s, 6H, Me), 3.19 (d, partially obscured,

1H, HfCH₂), 3.08 (d, J ) 10.2, 1H, HfCH₂). ¹H NMR (-85

°C): δ 8.65 (s br, 2H, H4), 8.00 (s, 2H, H6), 7.72 (br s, 2H,

H3), 7.68 (t, J ) 7.1, 1H, m-Ph), 7.15 (d, J ) 7.1, 1H, o-Ph),

6.72 (d, J ) 7.6, 1H, o-Ph), 6.67 (t, J ) 7.3, 1H, p-Ph), 6.54 (t,

J ) 7.6, 1H, m-Ph), 3.5 (br s, 3H, Me), 3.19 (d, J ) 10.0,

HfCH₂), 3.00 (d, J ) 10.0, HfCH₂), 2.9 (br s, 3H, Me). ¹³C NMR

(CD₂Cl₂): δ 164.9, 152.1, 148.5 (d, J _CF) 241, B(C₆F₅)₄^-), 143.2,

142.5, 138.6 (d, J _CF) 244, B(C₆F₅)₄^-), 136.7 (d, J _CF) 243,

B(C₆F₅)₄^-), 135.7, 135.5, 134.5, 131.1, 130.4, 127.1, 126.8, 124.0

(br), 112.7, 111.2, 77.0 (J _CH) 143, HfCH₂), 26.2.

1

Ox), 1.46 (s, 3H, MeBr₂Ox). The room-temperature H NMR

spectrum contains broad resonances characteristic of NMe₂-

Ph exchange.

[(MeOx)₂H f(CH ₂P h )][B(C₆F ₅)₄] (22a ). A mixture of

(MeOx)₂Hf(CH₂Ph)₂(10a , 0.141 g, 0.208 mmol) and [HNMePh₂]-

[B(C₆F₅)₄] (0.171 g, 0.198 mmol) in benzene (3 mL) was stirred

for 10 min at room temperature. A yellow oil separated. The

supernatant was removed by pipette, and the oil was washed

with benzene (3 mL) and dried under vacuum, yielding a

yellow solid (0.205 g, 80.4%). The ¹H NMR spectrum indicated

that this material contains 0.4 equiv of occluded benzene. Anal.

Calcd for C₅₁H₂₃BF₂₀N₂O₂Hf‚0.4C₆H₆: C, 49.48; H, 1.97; N,

2.16. Found: C, 49.42; H, 1.78; N, 2.31. ¹H NMR (CD₂Cl₂):

δ 8.56 (dd, J ) 7.8, 1.2, 1H, H7), 8.48 (d, J ) 8.5, 1H, H4),

8.34 (d, J ) 8.3, 1H, H4′), 7.92 (t, J ) 7.9, 1H, H6), 7.86 (dd,

J ) 8.3, 1.1, 1H, H5), 7.75 (t, J ) 7.9, 1H, H6′), 7.54 (m, 2H,

H5′ and H7′), 7.36 (d, J ) 8.5, 1H, H3), 7.01 (t, J ) 7.8, 2H,

m-Ph), 6.85 (d, J ) 8.3, 1H, H3′), 6.80 (d, J ) 7.1, 2H, o-Ph),

6.67 (t, J ) 7.4, 1H, p-Ph), 3.24 (d, J ) 11.3, 1H, HfCH₂), 2.90

(d, J ) 11.3, 1H, HfCH₂), 1.96 (s, 3H, Me), 0.53 (s, 3H, Me′).

¹³C NMR (CD₂Cl₂): δ 161.4, 161.2, 154.5, 150.2, 148.5 (d, J _CF

[(MeBr ₂Ox)₂Zr (CH₂P h )(P Me₃)][B(C₆F ₅)₄] (25a ). Ben-

zene (1.5 mL) was added to a solid mixture of (MeBr₂Ox)₂Zr-

(CH₂Ph)₂(11a , 0.332 g, 0.367 mmol) and [HNMePh₂][B(C₆F₅)₄]

(0.314 g, 0.364 mmol), and the mixture was stirred at room

temperature for 10 min. A yellow oil separated. The super-

natant was removed by pipette, and benzene (2 mL) was added

to the yellow oily residue. This mixture was exposed to PMe₃

(210 mmHg) on a vacuum line for 15 min. The solvent and

excess PMe₃were removed under vacuum, yielding a yellow

solid (0.490 g, 86.7%). An analytically pure sample was

obtained by washing this product with benzene and drying

under vacuum. Anal. Calcd for C₅₄H₂₈BBr₄F₂₀N₂O₂PZr: C,

) 240, B(C₆F₅)₄^-), 143.8, 143.4, 142.9, 140.0, 138.5 (d, J _CF

)

41.32; H, 1.80; N, 1.79. Found: C, 41.51; H, 1.89; N, 1.69. H

1

243, B(C₆F₅)₄^-), 136.2 (d, J _CF) 243, B(C₆F₅)₄^-), 136.0, 130.6,

130.6, 130.4, 129.5, 128.7, 128.1, 127.5, 126.2, 125.7, 125.1,

121.9, 120.7, 117.9, 81.7 (J _CH) 125, HfCH₂), 23.8, 22.5; the

B(C₆F₅)₄^-ipso-carbon was not observed. ¹⁹F NMR (CD₂Cl₂) δ

-132.9 (8F), -163.4 (4F), -167.3 (8F). ¹⁹F NMR (CD₂Cl₂, -90

°C): δ -133.4 (8F), -162.0 (4F), -166.0 (8F).

NMR (CD₂Cl₂): δ 8.57 (d, J ) 8.6, 1H, H4), 8.43 (d, J ) 8.6,

1H, H4′), 8.07 (s, 1H, H6 or H6′), 8.03 (s, 1H, H6 or H6′), 7.47

(t, J ) 7.6, 1H, m-Ph), 7.40 (d, J ) 8.5, 1H, H3), 7.29 (d, J )

8.7, 1H, H3′), 7.25 (d, J ) 7.5, 1H, o-Ph), 6.52 (d, J ) 7.6, 1H,

o-Ph), 6.51 (t, J ) 7.4, 1H, p-Ph), 6.31 (t, J ) 7.5, 1H, m-Ph),

3.50 (dd, J ) 9.4, 7.5, 1H, ZrCH₂), 3.29 (dd, J ) 7.5, 5.0, 1H,

ZrCH₂), 2.25 (s, 3H, MeBr₂Ox), 2.02 (s, 3H, Me′Br₂Ox), 1.26

(d, J _PH) 8.0, 9H, PMe₃). ¹³C NMR (CD₂Cl₂): δ 163.5, 160.9,

154.4, 153.9, 148.5 (d, J _CF) 238, B(C₆F₅)₄^-), 143.3, 142.9,

[(MeBr ₂Ox)₂Zr (CH₂P h )][B(C₆F ₅)₄] (23a ). Benzene (7 mL)

was added to a solid mixture of (MeBr₂Ox)₂Zr(CH₂Ph)₂(11a ,

0.451 g, 0.498 mmol) and [HNMePh₂][B(C₆F₅)₄] (0.428 g, 0.496

mmol), and the mixture was stirred for 10 min. A brown oil

separated. The supernatant was removed by pipette, and the

oil was washed with benzene (10 mL) and dried under vacuum,

yielding a yellow solid. The ¹H NMR spectrum established

that this material contained 1.4 equiv of occluded benzene.

Crystals of 23a suitable for X-ray diffraction were obtained

by recrystallization from CH₂Cl₂at -40 °C. Anal. Calcd for

141.3, 140.9, 138.5 (d, J _CF) 243, B(C₆F₅)₄^-), 136.7 (d, J _CF

)

243, B(C₆F₅)₄^-), 135.6, 135.5, 135.4, 134.2, 132.2, 132.1, 130.2,

129.8, 127.0, 126.3, 126.2, 126.0, 124.0 (br, B(C₆F₅)₄^-), 111.9,

110.8, 110.2, 109.9, 70.7 (J _PC) 9, J _CH) 145, ZrCH₂), 24.1,

23.8, 13.5 (J _PC) 21.0, PMe₃).

[(MeBr ₂Ox)₂Hf(CH₂P h )(P Me₃)][B(C₆F ₅)₄] (26a ). A mix-

ture of [(MeBr₂Ox)₂Hf(CH₂Ph)][B(C₆F₅)₄] (0.140 g, 0.089 mmol)

in benzene (3 mL) was exposed to PMe₃(150 mm Hg) on a

vacuum line for 15 min, with stirring at room temperature.

The volatiles were removed under vacuum, yielding a yellow

solid (0.105 g, 71.6%) which was shown by ¹H NMR to be >95%

pure 26a . ¹H NMR (CD₂Cl₂): δ 8.59 (d, J ) 8.6, 1H, H4), 8.44

(d, J ) 8.6, 1H, H4′), 8.11 (s, 1H, H6 or H6′), 8.07 (s, 1H, H6

or H6′), 7.41 (d, J ) 8.7, 1H, H3), 7.29 (d, J ) 8.6, 1H, H3′),

6.45 (t, J ) 7.6, 1H, p-Ph), 3.16 (dd, J ) 8, 5, 1H, HfCH₂),

2.98 (dd, J ) 8, 2, 1H, HfCH₂), 2.24 (s, 3H, MeBr₂Ox), 1.99 (s,

3H, Me′Br₂Ox), 1.29 (d, J _PH) 8.2, 9H, PMe₃); the m-Ph and

o-Ph resonances are not observed at room temperature due to

the η²-η¹benzyl isomerization. ¹H NMR (CD₂Cl₂, -50 °C):

δ 8.52 (d, J ) 8.6, 1H, H4), 8.36 (d, J ) 8.6, 1H , H4′), 8.03 (s,

1H, H6 or H6′), 7.97 (s, 1H, H6 or H6′), 7.39 (m, 3H, H3, o-Ph

and m-Ph), 7.28 (d, J ) 8.7, 1H, H3′), 6.47 (d, J ) 7.0, 1H,

o-Ph), 6.36 (t, J ) 7.0, 1H, p-Ph), 6.15 (t, J ) 7.0, 1H, m-Ph),

C

₅₁H₁₉BBr₄F₂₀N₂O₂Zr‚1.4C₆H₆: C, 44.51; H, 1.72; N, 1.75.

Found: C, 44.04; H, 1.78; N, 1.72. ¹H NMR (CD₂Cl₂): δ 8.71

(d, J ) 8.6, 2H, H4), 8.06 (s, 2H, H6), 7.73 (d, J ) 8.7, 2H,

H3), 6.9 (br, 2H, o-Ph), 6.86 (t, J ) 7.5, p-Ph), 3.56 (d, J ) 8.7,

1H, ZrCH₂), 3.46 (d, J ) 8.8, 1H, ZrCH₂), 3.16 (s, 6H, Me); the

m-Ph resonance is not observed at room temperature. ¹H

NMR (CD₂Cl₂, -85 °C): δ 8.71 (d, J ) 8.4, 1H, H4), 8.51 (d, J

) 8.3, 1H, H4), 7.98 (s, 1H, H6), 7.95 (s, 1H, H6), 7.82 (d, J )

8.6, 1H, H3), 7.71 (t, J ) 7.3, 1H, m-Ph), 7.59 (d, J ) 8.9, 1H,

H3), 7.00 (d, J ) 7.2, 1H, o-Ph), 6.77 (d, J ) 7.9, 1H, o-Ph),

6.72 (t, J ) 7.4, 1H, p-Ph), 6.60 (t, J ) 7.6, 1H, m-Ph), 3.55 (d,

J ) 8.4, 1H, ZrCH₂), 3.41(d, partially obscured, 1H, ZrCH₂),

3.38 (s, 3H, Me), 2.83 (s, 3H, Me). ¹³C NMR (CD₂Cl₂): δ 164.0,

152.8, 148.5 (d, J _CF) 240, B(C₆F₅)₄^-), 143.4, 142.2, 138.6 (d,

J _CF) 243, B(C₆F₅)₄^-), 136.6 (d, J _CF) 243, B(C₆F₅)₄^-), 135.4,

134.9, 130.6, 126.8, 126.8, 124.0 (br, B(C₆F₅)₄^-), 112.7, 110.0,

3302 Organometallics, Vol. 16, No. 15, 1997

Bei et al.

Ta ble 5. Su m m a r y of Cr ysta llogr a p h ic Da ta

(MeOx)₂Zr(CH₂Ph)₂(9a )

cmpd

empirical formula

fw

[(MeBr₂Ox)₂Zr(η²-CH₂Ph)][B(C₆F₅)₄] (23a )

C

₃₄H₃₀N₂O₂Zr

C₅₁H₁₉BBr₄F₂₀N₂O₂Zr

589.85

1493.4

cryst size (mm)

color/shape

space group

a (Å)

0.44 × 0.38 × 0.12

0.09 × 0.40 × 0.63

orange/prism

orange/hexagonal plate

Ph1

10.802(2)

P2₁/c

12.638(3)

b (Å)

13.767(3)

19.034(3)

c (Å)

10.332(2)

20.872(4)

R (deg)

74.92(2)

99.34(2)

104.15(2)

1430.5(9)

90

97.77(2)

90

5020(3)

â (deg)

γ (deg)

V (Å³)

Z

2

4

temperature (K)

diffractometer

radiation, λ

monochromator

2θ range (deg)

data collected h, k, l

total no. of reflns collected

no of unique reflns

R_int

293

200

Enraf-Nonius CAD-4

Mo KR, 0.710 73 Å

graphite

4 < 2θ < 50

-12 to 3, -15 to 16, -12 to 12

5784

4900

0.023

Enraf-Nonius CAD-4

Mo KR, 0.710 73 Å

graphite

4 < 2θ < 55

-16 to 1, -24 to 6, -27 to 27

16909

11431

0.030

no. of obs reflns, criterion

3709, I > 2σ(I)

6619, I > 2σ(I)

µ (cm^-1

)

4.08

34.85

abs corr factors (min/max)

abs corr method

structure soln^a

1.00/1.52

ψ scans

direct methods

FMLS on F, non-H anisotropic;

1.000/1.880

ψ scans

direct methods

refinement^b

FMLS on F, non-H anisotropic;

H isotropic

H47A, H47B isotropic; other H calculated

total no. of params

weighting scheme^c

R^d

472

738

p ) 0.02, q ) 0.0

p ) 0.03, q ) 0.0

0.0382

0.0475

1.11

0.73

0.09

0.044

0.049

1.53

0.77

0.05

e

R_w

GOF

max resid density (e/Å³)

max shift/ESD

a

MULTAN (Main, P.; Fiske, S. J .; Hull, S. E.; Lessinger, L.; Germain, G.; DeClercq, J . P.; Woolfson, M. M.; Multan80; University of

b

York: York, U.K., 1980). Data processing and refinement with MolEN (Fair, C. K.; MolEN Users Manual; Enraf-Nonius: Delft,

Netherlands, 1990); scattering factors taken from International Tables for X-Ray Crystallography; The Kynoch Press: Birmingham, U.K.,

d

1970; Vol. II. ^cw ) [(σ_F)²+ (pF)²+ q]^-1

.

Killean, R. C. G.; Lawrence, J . L. Acta. Crystallogr., Sect. B 1969, B25, 1750. R ) ∑(|F_o| -

|F_c|)/∑F_o. ^eR_w) {[∑(F_o- F_c)²]/[∑w(F_o)²]}^1/2

.

3.10 (t, J ) 9, 1H, HfCH₂), 2.86 (dd, J ) 9, 4, 1H, HfCH₂),

2.17 (s, 3H, MeBr₂Ox), 1.93 (s, 3H, MeBr₂Ox′), 1.22 (d, J ) 8,

9H, PMe₃). ¹³C NMR (CD₂Cl₂): δ 163.7, 161.5, 154.3, 154.1,

148.5 (d, J _CF) 242, B(C₆F₅)₄^-), 143.2, 143.1, 141.4, 141.0, 138.5

(d, J _CF) 242, B(C₆F₅)₄^-), 136.6 (d, J _CF) 243, B(C₆F₅)₄^-), 135.8,

135.6, 132.2 (br), 131.7, 130.1, 127.0, 126.5, 126.4, 126.1, 124.0

runs 12, 13, and 15, the solvent, Al(ⁱBu)₃, the catalyst, and

the cocatalyst were introduced to the reactor in that order

under 8 atm of ethylene. For run 14, the solvent, MAO, and

16 were introduced to the reactor in that order under 8 atm

of ethylene.

X-r a y Cr ysta llogr a p h y. Experimental data for the X-ray

diffraction analyses of 9a and 23a are summarized in Table

5.

(br, B(C₆F₅)₄^-), 111.7, 111.4, 111.2, 110.7, 71.8 (J _PC) 4, J _CH

)

141, HfCH₂), 24.0, 23.7, 13.2 (J _PC) 23, PMe₃); one aromatic

resonance was not observed.

Eth ylen e P olym er iza tion . Polymerization conditions and

results are summarized in Table 3. Entries 1-11 refer to

reactions which were performed in a Fischer-Porter ap-

paratus. In several cases, as summarized in Table 3, multiple

runs were performed to determine the reproducibility of the

yields and activities. A solution of the [(Ox)₂MR][B(C₆F₅)₄]

“active catalyst” was generated from the catalyst and cocata-

lyst as indicated in Table 3 and exposed to 2-3 atm of ethylene

at the desired temperature for 30 min. The polymerization

was quenched with acidic MeOH, and the polymer was

collected by filtration, washed with MeOH, and dried under

vacuum. Runs 12-15 were performed in a 1 L autoclave. For

Ack n ow led gm en t. This work was supported by the

Mitsubishi Chemical Corporation and the Department

of Energy (Grant No. DE-FG02-88ER13935).

Su p p or tin g In for m a tion Ava ila ble: Tables of atomic

coordinates and equivalent isotropic displacement parameters,

anisotropic displacement parameters, bond distances, bond

angles, and hydrogen atom coordinates and isotropic displace-

ment parameters for 9a and 23a (25 pages). Ordering

information is given on any current masthead page.

OM970235S

Article Doi

Synthesis, structures, bonding, and ethylene reactivity of group 4 metal alkyl complexes incorporating 8-quinolinolato ligands

DOI: 10.1021/om970235s

Source and publish data:

Authors:

Article abstract of DOI:10.1021/om970235s

Full text of DOI:10.1021/om970235s

Products guided by the article

R&D Labs maybe for 193352-00-0

Relevant to this article

Hot Product