Sterically encumbered (perfluoroaryl) borane and aluminate cocatalysts for tuning cation - Anion ion pair structure and reactivity in metallocene polymerization processes. A synthetic, structural, and polymerization study

J. Am. Chem. Soc. 1998, 120, 6287-6305

6287

Sterically Encumbered (Perfluoroaryl) Borane and Aluminate

Cocatalysts for Tuning Cation-Anion Ion Pair Structure and

Reactivity in Metallocene Polymerization Processes. A Synthetic,

Structural, and Polymerization Study

You-Xian (Eugene) Chen, Matthew V. Metz, Liting Li, Charlotte L. Stern, and

Tobin J. Marks*

Contribution from the Department of Chemistry, Northwestern UniVersity, EVanston, Illinois 60208-3113

ReceiVed October 31, 1997

Abstract: The synthesis and dialkyl abstraction chemistry as well as the unusual cocatalytic characteristics in

metallocene-mediated polymerization of two distinctive borane and aluminate cocatalysts tris(2,2′,2′′-

nonafluorobiphenyl)borane (PBB) and triphenyl carbenium tris(2,2′,2′′-nonafluorobiphenyl)fluoroaluminate,

(Ph₃C⁺PBA^-) are reported. Reaction of PBB with Cp′₂ThMe₂(Cp′ ) η⁵-C₅Me₅), CGCZrMe₂(CGC ) Me₂-

Si(η⁵-Me₄C₅)(^tBuN)), and Cp′MMe₃(M ) Zr, Hf) cleanly affords base-free cationic complexes

Cp′₂ThMe⁺MePBB^-(1), CGCZrMe⁺MePBB^-(5), and Cp′MMe₂⁺MePBB^-(M ) Zr, 7; Hf, 8). In case of

CGCTiMe₂and dimethyl zirconocenes, µ-methyl dinuclear cationic complexes [(CGCTiMe)₂(µ-Me)]⁺MePBB^-

(6) and [(L₂ZrMe)₂(µ-Me)]⁺MePBB^-(L ) η⁵-C₅H₅(Cp), 2; η⁵-1,2-Me₂C₅H₃(Cp′′), 3; Cp′, 4; L₂) Me₂Si-

(Ind)₂, Ind ) η⁵-C₉H₆, 9; L₂) Me₂C(Flu)(Cp), Flu ) η⁵-C₁₃H₈, 10) are formed. A similar reaction with

Ph₃C⁺PBA^-results in the corresponding complexes CGCZrCH₃⁺PBA^-(M ) Zr, 19; Ti, 20) and

L₂ZrCH₃⁺PBA^-(L ) Cp, 15b; Cp′′, 16; η⁵-1,3-(SiMe₂)₂C₅H₃, 17; Cp′, 18; L₂) Me₂Si(Ind)₂, 21; L₂) Me₂C-

(Flu)(Cp), 22). Two dinuclear complexes 3 and 13 ([Me₂C(Flu)(Cp)Zr(C₆F₅)]₂(µ-F)⁺MeB(C₆F₅)₃^-) derived

from borane PBB and B(C₆F₅)₃, respectively, and three other PBA^--based monomeric complexes 14

(Ph₃C⁺PBA^-), 19, and 21 have been characterized by X-ray diffraction, and these determinations allow detailed

analysis of the ion pairing in the solid state. In combination with solution dynamic NMR, all data indicate

MePBB^--cation interactions to be considerably weaker than those involving MeB(C₆F₅)₃^-, while the strongly

ion-paired chiral PBA^-converts previously enantiomeric cations into pairs of diastereomers. As revealed by

1

dynamic H NMR studies, ion pair reorganization/symmetrization in 5 is significantly more rapid than in the

MeB(C₆F₅)₃analogue, suggesting much looser ion pairing in 5. On the other hand, PBA^-racemization is

-

a rapid process (e.g., ∆G^‡(58 °C) ) 16.9(2) kcal/mol for 16), while cation-PBA^-ion pairs have higher

barriers for ion pair symmetrization than in analogous fluoroaryl borates. Dinuclear complexes 2 and 3 initiate

efficient polymerization of methyl methacrylate (MMA) to produce syndiotactic poly(methyl methacrylate)

(PMMA), while 9 produces highly isotactic PMMA, and sterically more accessible complexes 6 and 10 exhibit

no activity. For olefin polymerization and copolymerization, PBB-derived cationic complexes, both monomeric

and dinuclear, generally exhibit higher catalytic activity and comonomer incorporation levels than the

-

MeB(C₆F₅)₃analogues, with CGC catalysts exhibiting the greatest activity contrasts. On the other hand,

PBA^--derived complexes exhibit a remarkable sensitivity of olefin polymerization characteristics and ion pairing

to ancillary ligand bulk, with activity differences of up to 10⁶-fold observed. In regard to stereospecific

polymerization, PBA^--derived chiral complex 21 produces highly isotactic polypropylene while B(C₆F₅)₄

-

derived analogue produces isotactic polypropylene with lower isotacticity under similar conditions. Micro-

structure analyses of poly(ethylene-co-1-hexene) samples indicate that PBB enhances comonomer incorporation

randomness.

salts of B(C₆F₅)₄and related perfluoroarylborates^1b,5which

generate electron-deficient/coordinatively unsaturated “cationic”

complexes (A) as the actual catalysts.

-

Introduction

Growing evidence¹argues that the nature of the abstractor

and resulting anion X^-, as well as the coordinative/dynamic

features of cation-anion ion pairing (A; eq 1) significantly

influence the catalytic activity, lifetime, high-temperature stabil-

ity, chain-transfer characteristics, and stereoregulation in cationic

early transition metal-mediated homogeneous olefin polymer-

We have been particularly interested in isolable and X-ray

crystallographically characterizable catalysts for studying the

molecular basis of the polymerization catalysis.^1b,e,h,j,4aAmong

the aforementioned abstractors, it has not been possible to isolate

characterizable metallocene active species using MAO as the

activator, and very complicated, intractable species are produced

from MAO-activated reactions.^3,6Unlike MAO, B(C₆F₅)₄

-

based cocatalysts activate metallocene alkyls in a stoichiomet-

rically precise fashion; however, the reaction products have

proven difficult to isolate and characterize in a pure state,^1b,5b

presumably due to their poor thermal stability and poor

ization processes.²To date, effective abstractors include

methylalumoxane (MAO),³B(C₆F₅)₃,⁴and ammonium or trityl

Published on Web 06/11/1998

6288 J. Am. Chem. Soc., Vol. 120, No. 25, 1998

Chen et al.

crystallizability. In this regard, the reaction of B(C₆F₅)₃with a

variety of metallocene alkyls has been extensively studied

because the resulting catalytically active products are both

isolable and crystallographically characterizable^1a,c,e,h,4,7There-

fore, it would be of great interest to synthesize new boranes

with modified steric/electronic properties as well as trityl salts

of related anions that would afford isolable and informative

active catalysts.

of the resulting cationic complexes), characterization of solution

structural dynamics, solid state structural analyses, and poly-

merization studies.

In our continuing studies of metallocene cation-anion ion

pair structure and reactivity relationships, we focus here on anion

engineering and present a full account of our efforts to better

define the cation-anion interaction and subsequent effects on

polymerization, utilizing two complementary cocatalysts, a

sterically encumbered perfluoroaryl borane, tris(2,2′,2′′-perfluo-

robiphenyl)borane (PBB), and the trityl salt of the perfluoro-

arylfluoroaluminate, tris(2,2′,2′′-perfluorobiphenyl)fluoroalu-

minate (Ph₃C⁺PBA^-), to activate a variety of precatalysts

including bis-Cp, single ring, “constrained geometry”, C_2V, C₂,

and C_s-symmetric group 4 complexes.⁸The solution phase

molecular dynamics and the solid-state structures of the cation-

anion pairs as well as their performance in ethylene, propylene,

styrene, and methyl methacrylate polymerization, as well as

ethylene + 1-hexene and ethylene + styrene copolymerization

are analyzed in detail. Interesting results include the distinctive

abstraction chemistry of PBB and noncoordinating features of

MePBB^-, the chirality of PBA^-and its interplay with cation

stereochemistry, as well as the remarkable sensitivity of

polymerization characteristics (activity, stereoregulation, and

microstructure) to the experimentally determined cation-anion

ion pairing structures.

Additionally, exploring those steric and electronic charac-

teristics of anions which directly intrude into the metal cation

coordination sphere should be highly informative since the “fit”

and tightness of the cation-anion ion pairing is doubtless

connected, but in poorly understood ways, with the polymeri-

zation characteristics of the catalysts. Such cation-anion

interactions are likely modulated by the both cation ligand

framework and the anion architecture, which should be tunable

by selecting the appropriate cation-anion match to optimize

polymerization performance. Therefore, it would also be of

great interest to investigate and probe the properties of

sequentially modified ion pairs by means of synthesis (isolation

(1) (a) Sun, Y.; Spence, R. E. v. H.; Piers, W. E.; Parrez, H.; Yap, G. P.

A. J. Am. Chem. Soc. 1997, 119, 5132-5143. (b) Jia, L.; Yang, X.; Stern,

C. L.; Marks, T. J. Organometallics 1997, 16, 842-857. (c) Wang, Q.;

Gillis, D. J.; Quyoum, R.; Jeremic, D.; Tudoret, M.-J.; Baird, M. C. J.

Organomet. Chem. 1997, 527, 7-14. (d) Richardson, D. E.; Alameddin,

N. G.; Ryan, M. F.; Hayes, T.; Eyler, J. R.; Siedle, A. R. J. Am. Chem.

Soc. 1996, 118, 11244-11253. (e) Deck, P. A.; Marks, T. J. J. Am. Chem.

Soc. 1995, 117, 6128-6129. (f) Giardello, M. A.; Eisen, M. S.; Stern, C.

L.; Marks, T. J. J. Am. Chem. Soc. 1995, 117, 12114-12129. (g) Bochmann,

M.; Lancaster, S. L. Angew. Chem., Int. Ed. Engl. 1994, 33, 1634-1637.

(h) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1994, 116,

10015-10031. (i) Chien, J. C. W.; Song, W.; Rausch, M. D. J. Polym.

Sci., Part A: Polym. Chem. 1994, 32, 2387-2393. (j) Jia, L.; Yang, X.;

Stern, C. L.; Marks, T. J. Organometallics 1994, 13, 3755-3757. (k) Eisch,

J.; Pombrik, S. I.; Zheng, G.-X. Organometallics 1993, 12, 3856-3863.

(l) Herfert, N.; Fink, G. Makromol. Chem. 1992, 193, 773-778. (m) Horton,

A. D.; Orpen, A. G. Organometallics 1991, 10, 3910.

(2) For recent reviews, see: (a) Kaminsky, W.; Arndt, M. AdV. Polym.

Sci. 1997, 127, 144-187. (b) Bochmann, M. J. Chem. Soc., Dalton Trans.

1996, 255-270. (c) Brintzinger, H.-H.; Fischer, D.; Mu¨lhaupt, R.; Rieger,

B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143-1170.

(d) Guram, A. S.; Jordan, R. F. In ComprehensiVe Organometallic Chemistry

II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Elservier: Oxford,

1995; Chapter 12. (e) Soga, K., Terano, M., Eds. Catalyst Design for Tailor-

Made Polyolefins; Elsevier: Tokyo, 1994. (f) Mo¨hring, P. C.; Coville, N.

J. J. Organomet. Chem. 1994, 479, 1-29. (g) Marks, T. J. Acc. Chem. Res.

1992, 25, 57-65.

(3) (a) Kaminsky, W.; Kulper, K.; Brintzinger, H. H. Angew. Chem.,

Int. Ed. Engl. 1985, 24, 507-509. (b) Sinn, H.; Kaminsky, W. AdV.

Organomet. Chem. 1980, 18, 99-149.

(4) (a) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1991,

113, 3623-3625. (b) Ewen, J. A.; Elder, M. J. Chem. Abstr. 1991, 115,

136998g. (c) Massey, A. G.; Park, A. J. J. Organomet. Chem. 1964, 2,

245-250.

(5) (a) Chien, J. C. W.; Tsai, W.-M.; Rausch, M. D. J. Am. Chem. Soc.

1991, 113, 8570-8571. (b) Yang, X.; Stern, C. L.; Marks, T. J. Organo-

metallics 1991, 10, 840-842. (c) Ewen, J. A.; Elder, M. J. Eur. Pat. Appl.

1991, 426637; Chem. Abstr. 1991, 115, 136987c, 136988d. (d) Hlatky, G.

G.; Upton, D. J.; Turner, H. W. U.S. Pat. Appl. 1990, 459921; Chem. Abstr.

1991, 115, 256897v.

Experimental Section

Materials and Methods. All manipulations of air-sensitive materi-

als were performed with rigorous exclusion of oxygen and moisture in

flamed Schlenk-type glassware on a dual-manifold Schlenk line or

interfaced to a high-vacuum line (10^-6Torr), or in a nitrogen-filled

vacuum atmospheres glovebox with a high capacity recirculator (<1

ppm O₂). Argon, hydrogen (Matheson, prepurified), ethylene, and

propylene (Matheson, polymerization grade) were purified by passage

through a supported MnO oxygen-removal column and an activated

Davison 4A molecular sieve column. Ether solvents were purified by

distillation from Na/K alloy/benzophenone ketyl. Hydrocarbon solvents

(toluene and pentane) were distilled under nitrogen from Na/K alloy.

All solvents for high-vacuum line manipulations were stored in vacuo

over Na/K alloy in Teflon-valved bulbs. Deuterated solvents were

obtained from Cambridge Isotope Laboratories (all g99 atom %D),

were freeze-pump-thaw degassed, dried over Na/K alloy, and stored

in resealable flasks. Other nonhalogenated solvents were dried over

Na/K alloy, and halogenated solvents were distilled from P₂O₅and

stored over activated Davison 4A molecular sieves. C₆F₅Br (Aldrich)

was vacuum-distilled from P₂O₅. Styrene, methyl methacrylate, and

1-hexene (Aldrich) were dried over CaH₂and vacuum-transferred into

a storage tube containing activated 4A molecular sieves. TiCl₄, ZrCl₄,

BCl₃(1.0 M in hexane), AlCl₃, Ph₃CCl, PhCH₂MgCl (1.0 M in diethyl

n

ether), BuLi (1.6 M in hexanes), and MeLi (1.0 M in diethyl ether)

were purchased from Aldrich. Cp₂ZrMe₂,⁹Cp₂Zr(CH₂Ph)₂,¹⁰(1,2-

Me₂C₅H₃)₂ZrMe₂(Cp′′₂ZrMe₂),¹¹[1,3-(SiMe₂)₂C₅H₃]₂ZrMe₂(Cp₂

TMS

2

-

ZrMe₂),¹²(C₅Me₅)₂ThMe₂(Cp′₂ThMe₂),¹³Cp′₂ZrMe₂,¹⁴Cp′MMe₃(M

) Ti, Zr, Hf),¹⁵Me₂Si(C₅Me₄H)(^tBuNH)¹⁶(CGCH₂), Me₂Si(C₅Me₄)(^t-

BuN)TiMe₂¹⁷(CGCTiMe₂), CGCZrMe₂,¹⁷CGCMMe⁺MeB(C₆F₅)₃^-(M

(6) (a) Harlan, C. J.; Bott, S. G.; Barron, A. R. J. Am. Chem. Soc. 1995,

117, 6465-6474. (b) Sugano, T.; Matsubara, K.; Fugita, T.; Takahashi, T.

J. Mol. Catal. 1993, 82, 93-101. (c) Sishta, C.; Hathorn, R. M.; Marks, T.

J. J. Am. Chem. Soc. 1992, 114, 1112-1114.

(8) For preliminary communications of part of this study, see: (a) Chen,

Y.-X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1997, 119, 2582-

2583. (b) Chen, Y.-X.; Stern, C. L.; Yang, S.; Marks, T. J. J. Am. Chem.

Soc. 1996, 118, 12451-12452.

(7) (a) Bertuleit, A.; Fritze, C.; Erker, G.; Frohlich, R. Organometallics

1997, 16, 2900-2908. (b) Scollard, J. D.; McConville, D. H. J. Am. Chem.

Soc. 1996, 118, 10008-10009. (c) Beck, S.; Prosenc, M.-H.; Brintzinger,

H.-H.; Goretzki, R.; Herfert, N.; Fink, G. J. Mol. Catal. 1996, 111, 67-79.

(d) Wu, Z.; Jordan, R. F.; Petersen, J. L. J. Am. Chem. Soc. 1995, 117,

5867-5868. (e) Pellecchia, C.; Pappalardo, D.; Oliva, L.; Zambelli, A. J.

Am. Chem. Soc. 1995, 117, 6593-6594. (f) Temme, B.; Erker, G.; Karl,

J.; Luftmann, H.; Fro¨hlich, R.; Kotila, S. Angew. Chem., Int. Ed. Engl. 1995,

34, 1755-1757. (g) Bochmann, M.; Lancaster, S. J.; Hursthous, M. B.;

Malik, K. M. A. Organometallics 1994, 13, 2235-2243. (h) Gillis, D. J.;

Tudoret, M.-J.; Baird, M. C. J. Am. Chem. Soc. 1993, 115, 2543-2545.

(9) Samuel, E.; Rausch, M. D. J. Am. Chem. Soc. 1973, 95, 6263.

(10) Fachinetti, G.; Fochi, G.; Floriani, C. J. Chem. Soc., Dalton Trans.

1977, 1946-1950.

(11) Smith, G. M. Ph.D. Thesis, Northwestern University, 1985.

(12) (a) For dichloride, see: Antinolo, A.; Lappert, M. F.; Singh, A.;

Winterborn, D. J. W.; Engelhardt, L. M.; Raston, C. L.; White, A. H.; Carty,

A.; Taylor, N. J. J. Chem. Soc., Dalton Trans. 1987, 1643-1472. (b) The

corresponding dimethyl complex was synthesized by the reaction of

dichloride with excess of MeLi in toluene.

(13) Fagan, P. J.; Manriguez, J. M.; Maatta, E. A.; Seyam, A. M.; Marks,

T. J. J. Am. Chem. Soc. 1981, 103, 6650.

Metallocene Polymerization Processes

J. Am. Chem. Soc., Vol. 120, No. 25, 1998 6289

) Ti, Zr),^17arac-Me₂Si(Ind)₂ZrMe₂,¹⁸Me₂C(Flu)(Cp)ZrMe₂,¹⁹B(C₆F₅)₃,^4c

F-4), -150.13 (t, ³J_F-F) 21.7 Hz, 1 F, F-4′), -154.33 (t, ³J_F-F) 21.4

3

and Ph₃C⁺B(C₆F₅)₄^{- 5a}were prepared according to literature procedures.

Hz, 1 F, F-5), -160.75 (t, J_F-F) 23.9 Hz, 2 F, F-3′/F-5′).

To 2-bromononafluorobiphenyl (5.0 g, 12.7 mmol) in a mixed solvent

of 70 mL of diethyl ether and 70 mL of pentane was gradually added

8.0 mL of n-butyllithium (1.6 M in hexanes, 12.8 mmol) at -78 °C.

The mixture was stirred for an additional 2 h, and boron trichloride

(4.0 mL, 1.0 M in hexanes, 4.0 mmol) was then quickly added by

syringe. The mixture was stirred at -78 °C for 1 h, and the temperature

was then allowed to slowly rise to room temperature. A suspension

resulted after the mixture was stirred for an additional 12 h. It was

filtered to afford a yellow solution, and the solvent of the filtrate was

removed in vacuo. The resulting pale yellow powder or sticky solid

crude product (showing a clean ¹⁹F NMR spectrum) was sublimed at

140 °C/10^-4Torr or 125 °C/10^-6Torr to produce a light yelllow

crystalline solid as an ether-free crude product. Recrystallization from

pentane at -20 °C gave 3.5 g of the pure PBB as a colorless crystalline

solid, yield 91.0%. An alternate purification procedure involved

repeated sublimation. The first sublimation was found to remove the

coordinated ether, and the second sublimation afforded a faint yellow

crystalline solid. Analytical and spectroscopic data for PBB are as

Physical and Analytical Measurements. NMR spectra were

recorded on either Varian VXR 300 (FT 300 MHz, ¹H; 75 MHz, ¹³C)

or Germini-300 (FT 300 MHz, ¹H; 75 MHz, ¹³C; 282 MHz, ¹⁹F)

1

instruments. Chemical shifts for H and ¹³C spectra were referenced

to internal solvent resonances and are reported relative to tetrameth-

ylsilane. ¹⁹F NMR spectra were referenced to external CFCl₃. NMR

experiments on air-sensitive samples were conducted in Teflon valve-

sealed sample tubes (J. Young). Elemental analyses were performed

by Oneida Research Services, Inc., Whitesboro, NY. For ¹³C NMR

analyses of homopolymer microstructures, 40-60 mg polymer samples

were dissolved in 0.7 mL C₂D₂Cl₄with a heat gun in a 5-mm NMR

tube, and the samples were immediately transferrred to the NMR

spectrometer with the probehead preequilibrated at 120 °C. A 45° pulse

width and 2.5-s acquisition time were used with a pulse delay of 5 s.

Pentad signals were assigned according to literature criteria.²¹For ¹³

C

NMR analyses of copolymer microstructures, the samples were prepared

by dissolving 50 mg polymer samples in 0.7 mL C₂D₂Cl₄, and spectra

were taken at 100 °C with a 10-s pulse delay and a 90° pulse width.

Spectra were acquired with inverse-gated decoupling to avoid NOE

effects. Signals were assigned according to the literature for ethylene/

styrene²⁰and ethylene/1-hexene copolymers,²²respectively. Melting

temperatures of polymers were measured by DSC (DSC 2920, TA

Instruments, Inc.) from the second scan with a heating rate of 20 °C/

min. GPC analyses of polymer samples were performed at L. J.

Broutman & Associates Ltd., Chicago, on a Waters 150C GPC relative

to polystyrene standards.

Synthesis of Tris(2,2′,2′′-nonafluorobiphenyl)borane (PBB). In

a modification of the literature procedure,²³n-butyllithium (1.6 M in

hexanes, 25 mL, 40 mmol) was added dropwise to a 0 °C solution of

bromopentafluorobenzene (18.0 g, 9.1 mL, 72.9 mmol) in 100 mL of

diethyl ether. The mixture was then stirred for a further 12 h at room

temperature. Removal of solvent followed by vacuum sublimation at

60-65 °C/10^-4Torr gave 12.0 g of 2-bromononafluorobiphenyl as a

colorless crystalline solid, yield 83.3%. The dangerous and explosive

nature of C₆F₅Li ether solutions in this preparation can be avoided by

(a) the use of the excess of C₆F₅Br, (b) slow addition of n-butyllithium,

or (c) frequent change of the cold water bath or use of a continuous

flowing cold water bath. ¹⁹F NMR (C₆D₆, 23 °C): δ -126.77 (d, ³J_F-F

) 25.4 Hz, 1 F, F-3), -135.13 (d, ³J_F-F) 18.9 Hz, 1 F, F-6), -138.85

(d, ³J_F-F) 17.2 Hz, 2 F, F-2′/F-6′), -148.74 (t, ³J_F-F) 20.8 Hz, 1 F,

follows. ¹⁹F NMR (C₆D₆, 23 °C): δ -120.08 (s, br, 3 F, F-3), -132.09

3

(s, br, 3 F, F-6), -137.66 (s, br, 6 F, F-2′/F-6′), -143.31 (t, J_F-F

)

3

21.4 Hz, 3 F, F-4), -149.19 (t, J_F-F) 21.7 Hz, 3 F, F-4′), -150.56

(t, J_F-F) 14.7 Hz, 3 F, F-5), -160.72 (s, br, 6 F, F-3′/F-5′). ¹³C

3

1

2

NMR (C₆D₆, 23 °C): δ 150.92 (dd, J_C-F) 251.8 Hz, J_C-F) 10.1

Hz, 3 C), 146.35 (dd, ¹J_C-F) 254.3 Hz, ²J_C-F) 12.1 Hz, 3 C), 144.26

1

2

1

(dd, J_C-F) 258.1 Hz, J_C-F) 10.5 Hz, 6 C), 143.50 (tt, J_C-F

)

2

1

2

265.4 Hz, J_C-F) 12.0 Hz, 3 C), 141.98 (tt, J_C-F) 261.4 Hz, J_C-F

) 11.7 Hz, 3 C), 141.17 (tt, ¹J_C-F) 254.3 Hz, ²J_C-F) 10.5 Hz, 3 C),

137.70 (tt, ¹J_C-F) 257.3 Hz, ²J_C-F) 11.6 Hz, 6 C), 124.51 (d, ²J_C-F

) 11.7 Hz, 3 C), 113.60 (d, ²J_C-F) 11.5 Hz, 3 C), 106.05 (s, br, 3 C).

MS: parent ion at m/e 956. Anal. Calcd for C₃₆BF₂₇: C, 45.22; H,

0.00. Found: C, 45.44; H, 0.05.

Synthesis of Cp′₂ThMe⁺MePBB^-(1). Cp′₂ThMe₂(0.106 g, 0.199

mmol) and PBB (0.191 g, 0.199 mmol) were charged in the glovebox

into a 25-mL reaction flask having a filter frit, and the flask was

reattached to the high vacuum line. Benzene (15 mL) was then vacuum-

transferred into this flask at -78 °C. The mixture was slowly allowed

to warm to room temperatue and stirred for 6 h. The solvent was next

removed, pentane (20 mL) was vacuum-transferred into the flask, and

the mixture was filtered after stirring. The white solid which collected

was dried under vacuum to give 0.210 g of 1, yield 70.9%. ¹H NMR

(C₇D₈, 23 °C): δ 1.61 (s, 30 H, C₅Me₅), 0.62 (s, 3 H, Th-CH₃), -0.95

(s, br, 3 H, B-CH₃). ¹⁹F NMR (C₇D₈, 23 °C): δ -124.57 (s, br, 3 F),

(14) Manriquez, J. M.; McAlister, D. R.; Sanner, R. D.; Bercaw, J. E. J.

Am. Chem. Soc. 1978, 100, 2716-2724.

(15) (a) Mena, M.; Royo, P.; Serrano, R.; Pellinghelli, M. A.; Tiripicchio,

A. Organometallics 1989, 8, 476. (b) Schock, L. E.; Marks, T. J. J. Am.

Chem. Soc. 1988, 110, 7701. (c) Wolczanski, P. T.; Bercaw, J. E.

Organometallics 1982, 1, 793.

3

-138.10 (s, br, 3 F), -139.28 (d, J_F-F) 21.4 Hz, 3 F), -139.74 (d,

³J_F-F) 21.2 Hz, 3 F), -155.08 (t, ³J_F-F) 21.4 Hz, 3 F), -157.32 (t,

³J_F-F) 22.0 Hz, 3 F), -162.20 (t, ³J_F-F) 22.0 Hz, 3 F), -163.13 (t,

3

³J_F-F) 22.0 Hz, 3 F), -163.90 (t, J_F-F) 21.4 Hz, 3 F). ¹³C NMR

(16) (a) Shapiro, P. J.; Cotter, W. D.; Schaefer, W. P.; Labinger, J. A.;

Bercaw, J. E. J. Am. Chem. Soc. 1994, 116, 4623. (b) Piers, W. E.; Shapiro,

P. J.; Bunnel, E. E.; Bercaw, J. E. Synlett 1990, 2, 74. (c) Shapiro, P. J.;

Bunel, E. E.; Schaefer, W. P.; Bercaw, J. E. Organometallics 1990, 9, 867.

(17) (a) Fu, P.-F.; Wilson, D. J.; Rudolph, P. R.; Stern. C. L.; Marks, T.

J. Submitted for publication. (b) Canich, J. M.; Hlatky, G. G.; Turner, H.

W. PCT Appl. WO 92-00333, 1992. Canich, J. M. Eur. Patent Appl. EP

420 436-A1, 1991 (Exxon Chemical Co.). (c) Stevens, J. C.; Timmers, F.

J.; Wilson, D. R.; Schmidt, G. F.; Nickias, P. N.; Rosen, R. K.; Knight, G.

W.; Lai, S. Eur. Patent Appl. EP 416 815-A2, 1991 (Dow Chemical Co.).

(18) (a) Herrmann, W. A.; Ro¨hrmann, J.; Herdtweck, E.; Spaleck, W.;

Winter, A. Angew. Chem., Int. Ed. Engl. 1989, 28, 1511-1512. (b) Herfert,

N.; Fink, G. Makromol. Chem. Rapid Commun. 1993, 14, 91-96.

(19) (a) Razavi, A.; Thewalt, U. J. Organomet. Chem. 1993, 445, 111.

(b) Razavi, A.; Ferrara, J. J. Organomet. Chem. 1992, 435, 299.

(20) (a) Cheng, H. N.; Ewen, J. A. Makromol. Chem. 1989, 190, 1931.

(b) Ewen, J. A. J. Am. Chem. Soc. 1984, 106, 6355.

(21) (a) Pellecchia, C.; Pappalardo, D.; D’Arco, M.; Zambelli, A.

Macromolecules 1996, 29, 1158. (b) Miyatake, T.; Miaunuma, K.; Kakugo,

M. Macromol. Symp. 1993, 66, 203. (c) Kakugo, M.; Miyatake, T.;

Miaunuma, K. Stud. Surf. Sci. Catal. 1990, 56, 517. (d) Longo, P.; Grassi,

A. Makromol. Chem. 1990, 191, 2387. (e) Randall, J. C. J. Polym. Sci.,

Part B: Polym. Phys. 1975, 13, 889.

(22) (a) Soga, K.; Uozumi, T.; Park, J. R. Makromol. Chem. 1990, 191,

2853. (b) Hsich, E. T.; Randall, J. C. Macromolecules 1982, 15, 1402.

(23) Penton, D. E.; Park, A. J.; Shaw, D.; Massey, A. G. J. Organomet.

Chem. 1964, 2, 437-446.

(C₆D₆, 23 °C): δ 129.54 (C₅Me₅), 79.28 (Th-Me), 10.44 (C₅Me₅), 10.25

(B-Me). Anal. Calcd for C₅₈H₃₆BF₂₇Th: C, 46.79; H, 2.44. Found:

C, 46.68; H, 2.24.

Synthesis of [(L₂ZrMe)₂(µ-Me)]⁺MePBB^-: L ) Cp (2), L ) Cp′′

(3), and L ) Cp′ (4). In the glovebox, the L₂ZrMe₂complex (0.398

mmol) and PBB (0.199 mmol) were loaded into a 25-mL reaction flask

having a filter frit, and the flask was attached to the vacuum line.

Pentane (20 mL) was then vacuum-transferred into the flask at -78

°C. The mixture was slowly allowed to warm to room temperature

and stirred for an additional 2 h (L ) Cp), 15 h (L ) Cp′′), and 48 h

(L ) Cp′). The resulting suspension was filtered, and the colored solids

(light pink for 2, light yellow for 3, and yellow for 4) were washed

with a small amount of pentane and dried under vacuum, yields 90.3%

(2), 86.3% (3), and 34.7% (4). Analytical and spectroscopic data for

2 are as follows. ¹H NMR (C₆D₆, 23 °C): δ 5.65 (s, 20 H, C₅H₅),

-0.04 (s, 6 H, Zr-CH₃), -0.84 (s, br, 3 H, B-CH₃), -1.15 (s, 3 H,

3

Zr-CH₃-Zr). ¹⁹F NMR (C₆D₆, 23 °C): δ -124.20 (d, J_F-F) 16.6

Hz, 3 F), -138.98 (d, ³J_F-F) 20.3 Hz, 3 F), -139.20 (d, ³J_F-F) 22.0

Hz, 3 F), -140.29 (d, ³J_F-F) 24.5 Hz, 3 F), -155.15 (t, ³J_F-F) 20.9

Hz, 3 F), -160.06 (t, ³J_F-F) 22.3 Hz, 3 F), -162.79 (t, ³J_F-F) 22.0

Hz, 3 F), -163.11 (t, ³J_F-F) 21.5 Hz, 3 F), -163.97 (t, ³J_F-F) 19.0

Hz, 3 F). ¹³C NMR (C₆D₆, 23 °C): δ 113.24 (C₅H₅), 38.88 (Zr-CH₃),

21.53 (B-CH₃), 15.80 (Zr-CH₃-Zr). Anal. Calcd for C₆₀H₃₂BF₂₇-

6290 J. Am. Chem. Soc., Vol. 120, No. 25, 1998

Chen et al.

3

Zr₂: C, 49.39; H, 2.21 Found: C, 48.97; H, 1.92. Analytical and

spectroscopic data for 3 are as follows. ¹H NMR (C₇D₈, 23 °C): δ

5.51 (t, ³J_H-H) 2.8 Hz, 4 H, C₅H₃Me₂), 5.47 (t, ³J_H-H) 3.2 Hz, 4 H,

3 F), -164.00 (t, J_F-F) 22.3 Hz, 3 F). ¹³C NMR (C₇D₈, 23 °C): δ

121.89 (C₅Me₅), 49.59 (Hf-Me), 11.07 (C₅Me₅), 10.85 (B-Me). Anal.

Calcd for C₄₉H₂₄BF₂₇Hf‚¹/₄C₆H₆: C, 45.45; H, 1.93. Found: C, 45.16;

H, 2.08.

3

C₅H₃Me₂), 5.18 (t, J_H-H) 2.8 Hz, 4 H, C₅H₃Me₂), 1.73 (s, 12 H,

In Situ Generation of {[rac-Me₂Si(Ind)₂ZrMe]₂(µ-Me)}⁺MePBB^-

(9). rac-Me₂Si(Ind)₂ZrMe₂(8.2 mg, 0.020 mmol) and PBB (9.6 mg,

0.010 mmol) were loaded into a J. Young NMR tube and benzene-d₆

was condensed in. The mixture was allowed to react at room

temperature for 1 h before the NMR spectrum was recorded. A pair

of diastereomers was formed in a 2:1 ratio. ¹H NMR (C₆D₆, 23 °C)

C₅H₃Me₂), 1.51 (s, 12 H, C₅H₃Me₂), -0.26 (s, 6 H, Zr-CH₃), -0.92

(s, br, 3 H, B-CH₃), -1.50 (s, 3 H, Zr-CH₃-Zr). ¹⁹F NMR (C₆D₆,

3

23 °C): δ -123.37 (d, J_F-F) 15.3 Hz, 3 F), -139.20 (d, J_F-F

)

3

24.0 Hz, 3 F), -139.62 (d, J_F-F) 24.3 Hz, 3 F), -139.89 (d, J_F-F

) 24.0 Hz, 3 F), -155.81 (t, ³J_F-F) 21.4 Hz, 3 F), -159.36 (t, ³J_F-F

) 22.3 Hz, 3 F), -163.22 (t, ³J_F-F) 21.4 Hz, 3 F), -163.55 (t, ³J_F-F

) 22.0 Hz, 3 F), -164.20 (t, ³J_F-F) 22.6 Hz, 3 F). ¹³C NMR (C₆D₆,

for diastereomer A: δ 7.30-6.78 (m, 16 H, C₆H₄), 5.68 (d, J_H-H

)

1

23 °C): δ 114.20 (d, J_C-H) 171.7 Hz, C₅H₃Me₂), 113.62 (s, C₅H₃-

2.5 Hz, 4 H, C₅H₂), 5.31 (d, J_H-H) 2.5 Hz, 4 H, C₅H₂), 0.68 (s, 6 H,

SiMe₂), 0.47 (s, 6 H, SiMe₂), -0.83 (s, br, 3 H, B-CH₃), -0.92 (s, 6

H, Zr-CH₃), -2.87 (s, 3 H, Zr-CH₃-Zr). Diastereomer B: δ 7.30-

6.78 (m, 16 H, C₆H₄), 6.59 (d, J_H-H) 2.5 Hz, 4 H, C₅H₂), 5.93 (d,

J_H-H) 2.5 Hz, 4 H, C₅H₂), 0.67 (s, 6 H, SiMe₂), 0.44 (s, 6 H, SiMe₂),

-0.83 (s, br, 3 H, B-CH₃), -0.96 (s, 6 H, Zr-CH₃), -3.07 (s, 3 H,

1

Me₂), 112.80 (s, C₅H₃Me₂), 111.29 (d, J_C-H) 165.7 Hz, C₅H₃Me₂),

106.57 (d, ¹J_C-H) 173.3 Hz, C₅H₃Me₂), 41.63 (q, ¹J_C-H) 118.4 Hz,

1

Zr-CH₃), 31.26 (q, J_C-H) 116.5 Hz, B-CH₃), 22.21 (q, J_C-H

)

134.3 Hz, Zr-CH₃-Zr), 12.94 (q, ¹J_C-H) 128.0 Hz, C₅H₃Me₂), 12.71

(q, ¹J_C-H) 127.6 Hz, C₅H₃Me₂). Anal. Calcd for C₆₈H₄₈BF₂₇Zr₂: C,

51.98; H, 3.08. Found: C, 51.61; H, 3.00. Analytical and spectroscopic

data for 4 are as follows. ¹H NMR (C₆D₆, 23 °C): δ 1.57 (s, 60 H,

C₅Me₅), -0.84 (s, br, 3 H, B-CH₃). The bridging and terminal methyl

groups give rise to discrete signals at low temperature. ¹H NMR (C₇D₈,

-13 °C): δ -0.19 (s, br, 6 H, Zr-CH₃), -0.92 (s, br, 3 H, B-CH₃),

-2.42 (s, br, 3 H, Zr-CH₃-Zr). ¹⁹F NMR (C₆D₆, 23 °C): δ -123.11

Zr-CH₃-Zr). ¹⁹F NMR (C₆D₆, 23 °C): δ -123.00 (d, J_F-F) 17.5

3

Hz, 3 F), -139.28 (m, 6 F), -140.09 (d, ³J_F-F) 21.5 Hz, 3 F), -156.02

(t, ³J_F-F) 20.9 Hz, 3 F), -159.90 (t, ³J_F-F) 22.3 Hz, 3 F), -163.26

(t, ³J_F-F) 22.3 Hz, 3 F), -163.67 (t, ³J_F-F) 22.5 Hz, 3 F), -164.20

3

(t, J_F-F) 22.6 Hz, 3 F).

Synthesis of {[Me₂C(Flu)(Cp)ZrMe]₂(µ-Me)}⁺MePBB^-(10). In

the glovebox, Me₂C(Flu)(Cp)ZrMe₂(39.2 mg, 0.100 mmol) and PBB

(47.8 mg, 0.050 mmol) were loaded into a 25-mL reaction flask having

a filter frit, and the flask was reattached to the high vacuum line.

Benzene (20 mL) was then vacuum-transferred into the flask at -78

°C. The mixture was slowly allowed to warm to room temperatue

and stirred for an additional 2 h. The solvent was removed in vacuo

and pentane (20 mL) was condensed into the flask. The resulting

suspension was filtered, and the collected solid was washed with 5

mL of pentane and dried under vacuum to afford 73.9 mg of the title

complex, yield 80.5%. Two diastereomers are formed in a 1.8 (isomer

A):1 (isomer B) ratio. ¹H NMR (C₇D₈, 23 °C) for diastereomer A: δ

7.52 (t, J_H-H) 7.2 Hz, 4 H, C₆H₄), 7.30 (t, J_H-H) 7.2 Hz, 4 H, C₆H₄),

7.10 (t, J_H-H) 7.2 Hz, 4 H, C₆H₄), 7.09-6.86 (m, 6 H, C₆H₄), 6.23

(d, J_H-H) 2.4 Hz, 2 H, C₅H₄), 5.49 (d, J_H-H) 2.4 Hz, 2 H, C₅H₄),

5.17 (d, J_H-H) 2.4 Hz, 2 H, C₅H₄), 4.88 (d, J_H-H) 2.4 Hz, 2 H,

C₅H₄), 1.76 (s, 6 H, CMe₂), 1.62 (s, 6 H, CMe₂), -0.91 (s, br, 3 H,

B-CH₃), -1.21 (s, 6 H, Zr-CH₃), -3.38 (s, 3 H, Zr-CH₃-Zr).

Isomer B: δ 7.71 (d, J_H-H) 8.4 Hz, 4 H, C₆H₄), 7.61 (d, J_H-H) 8.4

Hz, 4 H, C₆H₄), 7.23 (t, J_H-H) 7.2 Hz, 4 H, C₆H₄), 7.09-6.86 (m, 6

H, C₆H₄), 6.17 (d, J_H-H) 2.4 Hz, 2 H, C₅H₄), 5.51 (d, J_H-H) 2.4 Hz,

2 H, C₅H₄), 5.08 (d, J_H-H) 2.4 Hz, 2 H, C₅H₄), 4.78 (d, J_H-H) 2.4

Hz, 2 H, C₅H₄), 1.78 (s, 6 H, CMe₂), 1.62 (s, 6 H, CMe₂), -0.91 (s,

br, 3 H, B-CH₃), -1.27 (s, 6 H, Zr-CH₃), -3.29 (s, 3 H, Zr-CH₃-

Zr). ¹⁹F NMR (C₇D₈, 23 °C): δ -123.56 (s, br, 3 F), -138.86 (d,

³J_F-F) 23.9 Hz, 3 F), -139.45 (d, ³J_F-F) 21.4 Hz, 3 F), -139.74 (d,

³J_F-F) 21.5 Hz, 3 F), -156.79 (t, ³J_F-F) 20.9 Hz, 3 F), -159.94 (t,

³J_F-F) 22.6 Hz, 3 F), -163.20 (t, ³J_F-F) 20.9 Hz, 3 F), -163.75 (t,

³J_F-F) 22.5 Hz, 3 F), -164.14 (t, ³J_F-F) 22.6 Hz, 3 F). Anal. Calcd

for C₈₂H₄₈BF₂₇Zr₂: C, 56.62; H, 2.78. Found: C, 55.80; H, 2.10.

Thermal Stability of Complex 3. Upon standing at 25 °C for 4

days or at 80 °C for 1 h, a solution of 3 in C₇D₈decomposed to yield

[(Cp′′₂ZrMe)₂(µ-F)]⁺MePBB^-(11), which was characterized both

spectroscopically and analytically from a scale-up synthesis in toluene.

(d, s, br, 3 F), -139.27 (d, ³J_F-F) 20.3 Hz, 3 F), -139.67 (t, ³J_F-F

)

25.1 Hz, 6 F), -155.73 (t, ³J_F-F) 20.9 Hz, 3 F), -160.91 (s, br, 3 F),

-163.25 (t, ³J_F-F) 21.7 Hz, 3 F), -163.56 (t, ³J_F-F) 22.0 Hz, 3 F),

3

-164.13 (t, J_F-F) 21.4 Hz, 3 F). Anal. Calcd for C₈₀H₇₂BF₂₇Zr₂:

C, 55.23; H, 4.17. Found: C, 54.81; H, 3.98.

Synthesis of CGCZrMe⁺MePBB^-(5) and [(CGCTiMe)₂(µ-

Me)]⁺MePBB^-(6). CGCZrMe₂(0.199 mmol) and PBB (0.199 mmol)

were reacted in the same manner as for the synthesis of 1 except for a

1

different reaction time (2 h) to yield 73.1% of 5 as a yellow solid. H

NMR (C₇D₈, 23 °C): δ 1.73 (s, 3 H, C₅Me₄), 1.69 (s, 3 H, C₅Me₄),

1.63 (s, 3 H, C₅Me₄), 1.43 (s, 3 H, C₅Me₄), 0.85 (s, 9 H, N-tBu), 0.28

(s, 3 H, SiMe₂), 0.21 (s, 3 H, SiMe₂), -0.48 (s, 3 H, Zr-CH₃), -0.95

(s, br, 3 H, B-CH₃). ¹⁹F NMR (C₇D₈, 23 °C): δ -124.20 (s, br, 3 F),

-139.14 (d, ³J_F-F) 23.7 Hz, 3 F), -139.35 (d, ³J_F-F) 22.0 Hz, 3 F),

-139.93 (d, ³J_F-F) 21.2 Hz, 3 F), -155.79 (t, ³J_F-F) 21.2 Hz, 3 F),

-159.67 (t, ³J_F-F) 22.3 Hz, 3 F), -163.28 (t, ³J_F-F) 21.7 Hz, 3 F),

-163.87 (t, ³J_F-F) 22.6 Hz, 3 F), -164.13 (t, ³J_F-F) 22.6 Hz, 3 F).

¹³C NMR (C₇D₈, 23 °C): δ 130.22 (C₅Me₄), 128.18 (C₅Me₄), 127.22

(C₅Me₄), 126.47 (C₅Me₄), 124.37 (C₅Me₄), 58.47 (N-CMe₃), 34.37

(Zr-CH₃), 34.10 (N-CMe₃), 15.89 (C₅Me₄), 13.46 (C₅Me₄), 11.77

(C₅Me₄), 10.99 (C₅Me₄), 7.92 (SiMe₂), 5.65 (SiMe₂). Anal. Calcd for

C₅₃H₃₃BF₂₇NSiZr: C, 47.97; H, 2.51; N, 1.06. Found: C, 47.79; H,

2.58; N, 0.86. The synthesis, spectroscopic, and analytical data for 6

were previously described in detail.²⁴

Synthesis of Cp′MMe₂⁺MePBB^-: M ) Zr (7) and Hf (8).

Cp′MMe₃(0.199 mmol) and PBB (0.191 g, 0.199 mmol) were reacted

in the same manner as for the synthesis of 1 to produce 0.174 g of 7

and 0.144 g of 8 as yellow solids in yields of 69.1% and 43.6%,

respectively. An NMR-scale reaction showed quantitative formation

of 7 and 8. Analytical and spectroscopic data for 7 are as follows. ¹H

1

NMR (C₇D₈, 23 °C): δ 7.14 (s, 3 H, /₂C₆H₆), 1.40 (s, 15 H, C₅Me₅),

-0.60 (s, 6 H, Zr-CH₃), -0.95 (s, br, 3 H, B-CH₃). ¹⁹F NMR (C₇D₈,

23 °C): δ -124.21 (d, ³J_F-F) 21.5 Hz, 3 F), -139.06 (t, ³J_F-F) 24.5

Hz, 6 F), -140.10 (d, ³J_F-F) 23.7 Hz, 3 F), -155.42 (t, ³J_F-F) 20.9

¹H NMR (C₇D₈, 23 °C): δ 5.68 (t, J_H-H) 2.8 Hz, 4 H, C₅H₃Me₂),

3

5.36 (t, ³J_H-H) 3.1 Hz, 4 H, C₅H₃Me₂), 5.23 (t, ³J_H-H) 2.8 Hz, 4 H,

C₅H₃Me₂), 1.71 (s, 12 H, C₅H₃Me₂), 1.43 (s, 12 H, C₅H₃Me₂), 0.12 (d,

³J_H-F) 2.1 Hz, 6 H, Zr-CH₃), -0.92 (s, br, 3 H, B-CH₃). ¹⁹F NMR

spectrum is the same as that of 3 except there is an extra peak at -91.27

ppm (s) for the bridging F signal. ¹³C NMR (C₇D₈, 23 °C): δ 117.74

(C₅H₃Me₂), 114.33 (C₅H₃Me₂), 112.14 (C₅H₃Me₂), 111.45 (C₅H₃Me₂),

108.01 (C₅H₃Me₂), 42.11 (Zr-CH₃), 34.43 (B-CH₃), 12.63 (C₅H₃Me₂),

12.45 (C₅H₃Me₂). Anal. Calcd for C₆₇H₄₅BF₂₈Zr₂: C, 51.09; H, 2.88.

Found: C, 50.71; H, 2.61.

3

Hz, 3 F), -159.66 (s br, 3F), -163.14 (t, J_F-F) 21.5 Hz, 3 F),

-163.54 (t, ³J_F-F) 24.5 Hz, 3 F), -163.93 (t, ³J_F-F) 21.7 Hz, 3 F).

¹³C NMR (C₇D₈, 23 °C): δ 128.29 (d, ¹J_C-H) 158.2 Hz, C₆H₆), 123.13

1

(s, C₅Me₅), 45.07 (q, J_C-H) 119.8 Hz, Zr-CH₃), 11.31 (q, J_C-H

)

127.38 Hz, C₅Me₅). Anal. Calcd for C₄₉H₂₄BF₂₇Zr‚¹/₂C₆H₆: C, 49.30;

H, 2.15. Found: C, 49.18; H, 2.07. Analytical and spectroscopic data

for 8 are as follows. ¹H NMR (C₇D₈, 23 °C): δ 7.14 (s, 1.5 H, ¹/₄C₆H₆),

1.46 (s, 15 H, C₅Me₅), -0.84 (s, 6 H, Hf-CH₃), -0.95 (s, br, 3 H,

B-CH₃). ¹⁹F NMR (C₇D₈, 23 °C): δ -124.14 (d, ³J_F-F) 21.4 Hz, 3

F), -139.29 (t, J_F-F) 22.6 Hz, 6 F), -140.12 (d, J_F-F) 24.5 Hz,

3 F), -155.52 (t, ³J_F-F) 21.4 Hz, 3 F), -159.69 (t, ³J_F-F) 22.6 Hz,

3 F), -162.91 (t, ³J_F-F) 21.4 Hz, 3 F), -163.49 (t, ³J_F-F) 23.1 Hz,

In Situ Generation of Me₂C(Flu)(Cp)ZrMe⁺MeB(C₆F₅)₃(12).

-

3

Me₂C(Flu)(Cp)ZrMe₂(3.9 mg, 0.010 mmol) and B(C₆F₅)₃(5.1 mg,

0.010 mmol) were loaded in the glovebox into a J. Young NMR tube,

and toluene-d₈was condensed in. The mixture was allowed to react

at room temperature for 1 h before the NMR spectrum was recorded.

(24) Chen, Y.-X.; Marks, T. J. Organometallics 1997, 16, 3649-3657.

Metallocene Polymerization Processes

J. Am. Chem. Soc., Vol. 120, No. 25, 1998 6291

¹H NMR (C₇D₈, 23 °C): δ 7.64 (d, J_H-H) 8.5 Hz, 1 H, C₆H₄), 7.59

(d, J_H-H) 8.5 Hz, 1 H, C₆H₄), 7.13 (d, J_H-H) 6.3 Hz, 1 H, C₆H₄),

7.01 (d, J_H-H) 8.2 Hz, 1 H, C₆H₄), 6.91 (d, J_H-H) 8.3 Hz, 1 H,

C₆H₄), 6.73 (t, J_H-H) 7.7 Hz, 1 H, C₆H₄), 6.63 (t, J_H-H) 7.1 Hz, 1

H, C₆H₄), 6.41 (t, J_H-H) 8.2 Hz, 1 H, C₆H₄), 5.93 (d, J_H-H) 3.0 Hz,

1 H, C₅H₄), 5.54 (d, J_H-H) 3.0 Hz, 1 H, C₅H₄), 5.19 (d, J_H-H) 3.0

Hz, 1 H, C₅H₄), 4.45 (d, J_H-H) 3.0 Hz, 1 H, C₅H₄), 1.50 (s, 3 H,

CMe₂), 1.46 (s, 3 H, CMe₂), -0.53 (s, br, 3 H, B-CH₃), -0.92 (s, 6

) 21.4 Hz, 3 F), -162.52 (t, ³J_F-F) 24.5 Hz, 3 F). ¹³C NMR (C₆D₆,

23 °C): δ 130.23 (s, ipso-Ph), 129.20 (d, J_C-H) 156.2 Hz, m-Ph),

128.26 (d, J_C-H) 157.1 Hz, o-Ph), 125.42 (d, J_C-H) 158.1 Hz, p-Ph),

114.77(d, J_C-H) 176.5 Hz, Cp), 66.68 (t, J_C-H) 122.8 Hz, -CH₂).

Anal. Calcd for C₅₃H₁₇AlF₂₈Zr: C, 48.82; H, 1.31. Found: C, 48.77;

H, 1.36. The synthetic procedure for Cp₂ZrCH₃⁺PBA^-(15b) was the

same as that of the synthesis of 15a above. ¹H NMR (C₇D₈, 23 °C):

3

δ 5.56 (s, 5 H, Cp), 5.48 (s, 5 H, Cp), 0.44 (d, J_H-F) 2.2 Hz, 3 H,

H, Zr-CH₃). ¹⁹F NMR (C₇D₈, 23 °C): δ -133.39 (d, J_F-F) 22.60

Zr-CH₃). ¹⁹F NMR (C₇D₈, 23 °C): δ -117.76 (t, ³J_F-F) 21.5 Hz, 3

3

Hz, 6 F, o-F), -159.60 (t, J_F-F) 20.6 Hz, 3 F, p-F), -164.62 (t,

F), -133.36 (t, J_F-F) 18.3 Hz, 3 F), -138.11 (s, br, 1 F, Al-F),

³J_F-F) 18.3 Hz, 6 F, m-F).

-138.90 (s, 3 F), -139.40 (t, ³J_F-F) 21.4 Hz, 3 F), -152.15 (t, ³J_F-F

) 14.9 Hz, 3 F), -153.08 (t, ³J_F-F) 21.2 Hz, 3 F), -154.06 (t, ³J_F-F

) 21.4 Hz, 3 F), -160.80 (d, ³J_F-F) 15.3 Hz, 3 F), -162.69 (t, ³J_F-F

) 21.4 Hz, 3 F).

Thermal Stability of Complex 12. In an attempt to grow single

crystals of isolated complex 12 from toluene over a course of two

weeks, red crystals formed. These were found by single-crystal

diffraction not to be 12 but to be an unusual fluoride-abstrac-

tion, fluoroaryl-transfer product, dinuclear cationic complex

Synthesis of Cp′′₂ZrCH₃⁺PBA^-(16). This procedure was the same

as for the synthesis of 15 above, yield 81.7%. ¹H NMR (C₂D₂Cl₄, 23

°C): δ 5.95 (s, br, 1 H, C₅H₃Me₂), 5.77 (s, br, 1 H, C₅H₃Me₂), 5.72 (s,

br, 1 H, C₅H₃Me₂), 5.46 (s, br, 1 H, C₅H₃Me₂), 5.70 (s, br, 1 H, C₅H₃-

Me₂), 5.40 (s, br, 1 H, C₅H₃Me₂), 2.11 (s, 3 H, C₅H₃Me₂), 1.98 (s, 3 H,

C₅H₃Me₂), 1.76 (s, 3 H, C₅H₃Me₂), 1.70 (s, 3 H, C₅H₃Me₂), 0.28 (d,

¹J_C-H) 120.3 Hz, Zr-¹³CH₃). ¹⁹F NMR (C₇D₈, 23 °C): δ -116.20

(t, ³J_F-F) 20.7 Hz, 3 F), -133.54 (t, ³J_F-F) 15.2 Hz, 3 F), -138.67

(t, ³J_F-F) 25.4 Hz, 3 F), -139.42 (t, ³J_F-F) 22.0 Hz, 3 F), -143.38

{[Me₂C(Flu)(Cp)Zr(C₆F₅)]₂(µ-F)}⁺MeB(C₆F₅)₃(13).

-

Synthesis of Triphenylcarbenium Tris(2,2′,2′′-nonafluorobiphe-

nyl)fluoroaluminate Ph₃C⁺[(C₁₂F₉)₃AlF]^-(Ph₃C⁺PBA^-, 14). To

2-bromononafluorobiphenyl (8.29 g, 21.0 mmol) in a mixed solvent

of 70 mL of diethyl ether and 70 mL of pentane was gradually added

13.2 mL of n-butyllithium (1.6 M in hexanes, 21.0 mmol) at -78 °C.

The mixture was stirred for an additional 2 h, and aluminum trichloride

(0.67 g, 5.0 mmol) was then quickly added. The mixture was stirred

at -78 °C for 1 h, and the temperature was then allowed to slowly

rise to room temperature. A white suspension resulted after stirring

for an additional 12 h. The mixture was filtered, and the solvent

removed from the filtrate in vacuo. To the yellow sticky residue was

added 100 mL of pentane, and the mixture was stirred for 1 h. The

resulting white solid was collected by filtration and dried in vacuo to

3

(s, br, 1 F, Al-F), -152.67 (t, J_F-F) 17.5 Hz, 3 F), -153.37 (t,

³J_F-F) 21.4 Hz, 3 F), -154.45 (t, ³J_F-F) 20.3 Hz, 3 F), -161.20 (d,

³J_F-F) 21.4 Hz, 3 F), -162.92 (t, ³J_F-F) 22.0 Hz, 3 F). Anal. Calcd

for C₅₁H₂₁AlF₂₈Zr: C, 47.71; H, 1.65. Found: C, 47.46; H, 1.37.

Cp^TMS₂ZrCH₃⁺PBA^-(17) decomposes in toluene solution within

2

2 h at 25 °C and undergoes rapid decomposition to a myriad of

unidentified products at higher temperatures. Characterization of the

complex is based on very clean NMR-scale reactions. Complex 17

was generated in situ for polymerization studies. ¹H NMR (C₇D₈, 23

°C): δ 6.88 (s, br, 1 H, C₅H₃TMS₂), 6.71 (t, J_H-H) 2.1 Hz, 1 H, C₅H₃-

TMS₂), 6.31 (s, br, 1 H, C₅H₃TMS₂), 6.23 (s, br, 1 H, C₅H₃TMS₂),

5.79 (s, br, 1 H, C₅H₃TMS₂), 5.71 (s, br, 1 H, C₅H₃TMS₂), 0.70 (s, br,

3 H, Zr-CH₃), 0.17 (s, 3 H, C₅H₃TMS₂), 0.10 (s, 3 H, C₅H₃TMS₂),

-0.05 (s, 3 H, C₅H₃TMS₂), -0.07 (s, 3 H, C₅H₃TMS₂). ¹⁹F NMR (C₇D₈,

23 °C): δ -112.12 (d, ³J_F-F) 12.2 Hz, 3 F), -133.22 (t, ³J_F-F) 15.5

Hz, 3 F), -137.49 (s, 3 F), -138.40 (t, ³J_F-F) 21.7 Hz, 3 F), -144.23

give 3.88 g of Ar^FFAl^-Li⁺‚OEt₂, yield 72.4%. ¹H NMR (C₇D₈, 23

3

°C): δ 2.84 (q, J_H-H) 7.2 Hz, 4 H, 2-CH₂O), 0.62 (t, J_H-H) 7.2 Hz,

6 H, 2CH₂CH₂O-). ¹⁹F NMR (C₆D₆, 23 °C): δ -122.80 (s, br, 3 F,

F-3), -134.86 (s, 3 F, F-6), -139.12 (s, 6 F, F-2′/F-6′), -153.95 (t,

3

³J_F-F) 18.3 Hz, 3 F, F-4), -154.52 (t, J_F-F) 20.2 Hz, 6 F, F-4′/F-

5), -162.95 (s, 6 F, F-3′/F-5′), -176.81 (s, br, 1 F, Al-F). The above

lithium salt (1.74 g, 1.62 mmol) and Ph₃CCl (0.48 g, 1.72 mmol) were

suspended in pentane and stirred overnight, and the resulting orange

solid was collected by filtration and washed with pentane. The crude

product was then redissolved in CH₂Cl₂and filtered through Celite to

remove LiCl, followed by pentane addition to precipitate the orange

solid. Recrystallization from CH₂Cl₂/pentane at -78 °C overnight gave

1.56 g of orange crystals of the title compound, yield 70.5%. ¹H NMR

(CDCl₃, 23 °C): δ 8.25 (t, J_H-H) 7.5 Hz, 3 H, p-H, Ph), 7.86 (t, J_H-H

) 7.5 Hz, 6 H, m-H, Ph), 7.64 (dd, J_H-H) 8.4 Hz, J_H-H) 1.2 Hz, 6

H, o-H, Ph), 1.28 (m), 0.88(t) (pentane residue). ¹⁹F NMR (CDCl₃,

23 °C): δ -121.05 (s, 3 F, F-3), -139.81 (s, 3 F, F-6), -141.19 (s, 6

F, F-2′/F-6′), -156.93 (t, ³J_F-F) 18.3 Hz, 6 F, F-4/F-4′), -158.67 (s,

3 F, F-5), -165.32 (s, 6 F, F-3′/F-5′), -175.60 (s, br, 1 F, Al-F).

Anal. Calcd for C₆₀H₁₅AlF₂₈‚C₅H₁₂: C, 57.12; H, 1.99. Found: C,

57.16; H, 1.43.

Synthesis of Cp₂ZrCH₂Ph⁺PBA^-(15a). Cp₂Zr(CH₂Ph)₂(0.081

g, 0.20 mmol) and Ph₃C⁺PBA^-(0.261 g, 0.200 mmol) were charged

in the glovebox into a 25-mL reaction flask with a filter frit, and the

flask was reattached to the high-vacuum line. Toluene (15 mL) was

then vacuum-transferred into this flask at -78 °C. The mixture was

slowly allowed to warm to room temperature and stirred for 4 h. The

volume of toluene was next reduced to 5 mL, and 10 mL of pentane

was condensed into the flask at -78 °C. The suspension which formed

was quickly filtered, and the orange crystalline solid which collected

was dried under vacuum overnight, yield 0.22 g (84%). Large orange

crystals were obtained by slow cooling a pentane solution of the

compound to -20 °C over a period of several days. ¹H NMR (C₆D₆,

23 °C): δ 6.95 (t, J_H-H) 7.8 Hz, 2 H, m-H, Ph), 6.80 (t, J_H-H) 7.5

Hz, 1 H, p-H, Ph), 6.46 (d, J_H-H) 7.2 Hz, 2 H, o-H, Ph), 5.45 (s, 5

H, Cp), 5.42 (s, 5 H, Cp), 2.47 (d, J_H-H) 11.4 Hz, 1 H, -CH₂), 1.92

(d, J_H-H) 11.4 Hz, 1 H, -CH₂). ¹⁹F NMR (C₆D₆, 23 °C): δ -117.09

(t, ³J_F-F) 20.5 Hz, 3 F), -133.17 (t, ³J_F-F) 15.2 Hz, 3 F), -138.60

(d, ³J_F-F) 27.3 Hz, 3 F), -139.53 (t, ³J_F-F) 21.2 Hz, 3 F), -146.34

(s, br, 1 F, Al-F), -152.01 (t, ³J_F-F) 24.3 Hz, 3 F), -153.15(t, ³J_F-F

) 20.9 Hz, 3 F), -153.92 (t, ³J_F-F) 18.3 Hz, 3 F), -160.82 (d, ³J_F-F

3

(s, br, 1 F, Al-F), -153.41 (m, 6 F), -154.15 (t, J_F-F) 21.2 Hz, 3

3

F), -161.80 (d, J_F-F) 18.3 Hz, 3 F), -162.82 (t, J_F-F) 21.4 Hz,

3 F).

Cp′₂ZrCH₃⁺PBA^-(18) is too thermally unstable at 25 °C to isolate.

The H NMR monitored reaction of Cp′₂ZrMe₂and Ph₃C⁺PBA^-in

1

C₂D₂Cl₄clearly reveals the formation of Ph₃C-CH₃(δ 2.15) and a

+

broad singlet at δ 0.25 ppm assignable to the ZrCH₃group. More

than four Cp methyl resonances at δ 1.97-1.72 ppm having different

relative intensities are observed, indicating decomposition. Complex

18 was generated in situ for polymerization studies. ¹⁹F NMR (C₂D₂-

Cl₄, 23 °C): δ -114.77 (s, br, 3 F), -132.11 (t, ³J_F-F) 15.2 Hz, 3 F),

3

-136.84 (t, J_F-F) 22.0 Hz, 3 F), -137.29 (s, br, 3 F), -150.90 (t,

³J_F-F) 20.9 Hz, 3 F), -151.85 (t, ³J_F-F) 23.9 Hz, 3 F), -152.47 (t,

3

³J_F-F) 24.5 Hz, 3 F), -155.78 (s, br, 1 F, Al-F), -160.02 (d, J_F-F

3

) 16.5 Hz, 3 F), -161.06 (t, J_F-F) 21.2 Hz, 3 F).

Synthesis of CGCZrCH₃⁺PBA^-(19). CGCZrMe₂(0.148 g, 0.400

mmol) and Ph₃C⁺PBA^-(0.523, 0.400 mmol) were reacted in the same

manner as for the synthesis of 15 above to yield 0.35 g of the title

complex as a colorless crystalline solid, yield 64.8%. The complex is

quite soluble in pentane, and cold pentane was used to wash the product.

Two diastereomers are found in a 2.9:1 ratio. ¹H NMR (C₇D₈, 23 °C)

for diastereomer A (74%): δ 1.98 (s, 3 H, Me₄C₅), 1.82 (s, 3 H, Me₄C₅),

1.76 (s, 3 H, Me₄C₅), 1.27(s, 3 H, Me₄C₅), 0.93 (s, 9 H, ^tBu-N), 0.24

(s, 3 H, SiMe₂), 0.18 (s, 3 H, SiMe₂), 0.15 (s, 3 H, Zr-CH₃). Isomer

B (26%): δ 2.01 (s, 3 H, Me₄C₅), 1.92 (s, 3 H, Me₄C₅), 1.73 (s, 3 H,

Me₄C₅), 1.24 (s, 3 H, Me₄C₅), 0.93 (s, 9 H, N-^tBu), 0.34 (s, 3 H,

Zr-CH₃), 0.24 (s, 3 H, SiMe₂), 0.18 (s, 3 H, SiMe₂). ¹⁹F NMR (C₇D₈,

23 °C): δ -108.92 (s, br), -114.50 (s, br), -117.26 (s, br), -133.19

(t, ³J_F-F) 12.1 Hz), -138.69 (s, br, Al-F), -139.25 (s, br), -152.53

(t, ³J_F-F) 21.2 Hz), -153.00 (d, ³J_F-F) 21.4 Hz), -153.76 (t, ³J_F-F

3

) 24.3 Hz), -160.94 (t, J_F-F) 22.6 Hz), -162.80 (t, J_F-F) 21.4

Hz). ¹³C NMR (C₇D₈, 23 °C): δ 130.19 (Me₄C₅), 128.09 (Me₄C₅),

6292 J. Am. Chem. Soc., Vol. 120, No. 25, 1998

Chen et al.

127.18 (Me₄C₅), 126.44 (Me₄C₅), 124.33 (Me₄C₅), 56.63 (N-CMe₃),

40.70, 38.58 (q, J_C-H) 120.8 Hz, Zr-CH₃), 32.70 (q, J_C-H) 120.6

fluorenyl region could not be assigned due to overlap between the

signals of the two isomers as well as with those of triphenylethane. ¹H

NMR (C₇D₈, 23 °C) for diastereomer A: δ 6.20 (d, J_H-H) 2.7 Hz, 1

H, C₅H₄), 5.44 (d, J_H-H) 2.7 Hz, 1 H, C₅H₄), 4.84 (d, J_H-H) 2.7 Hz,

1 H, C₅H₄), 4.61 (d, J_H-H) 2.7 Hz, 1 H, C₅H₄), 1.60 (s, 3 H, CMe₂),

1.43 (s, 3 H, CMe₂), -1.03 (s, 3 H, Zr-CH₃). Diastereomer B: δ

6.32 (d, J_H-H) 2.7 Hz, 1 H, C₅H₄), 5.21 (d, J_H-H) 2.7 Hz, 1 H,

C₅H₄), 4.98 (d, J_H-H) 2.7 Hz, 1 H, C₅H₄), 4.56 (d, J_H-H) 2.7 Hz, 1

H, C₅H₄), 1.65 (s, 3 H, CMe₂), 1.49 (s, 3 H, CMe₂), -1.07 (s, 3 H,

Zr-CH₃). ¹⁹F NMR (C₇D₈, 23 °C): δ -115.99 (m, br), -131.32 (s,

Hz, N-CMe₃), 15.75 (q, J_C-H) 127.9 Hz, Me₄C₅), 14.05 (q, J_C-H

)

128.0 Hz, Me₄C₅), 12.00 (q, J_C-H) 127.8 Hz, Me₄C₅), 10.18 (q, J_C-H

) 128.1 Hz, Me₄C₅), 8.49 (q, J_C-H) 121.0 Hz, SiMe₂), 6.52 (q, J_C-H

) 120.9 Hz, SiMe₂). Anal. Calcd for C₅₂H₃₀AlF₂₈NSiZr: C, 46.37;

H, 2.25; N, 1.04. Found: C, 46.65; H, 2.13; N, 0.89.

Synthesis of CGCTiCH₃⁺PBA^-(20). CGCTiMe₂(0.065 g, 0.20

mmol) and Ph₃C⁺PBA^-(0.261, 0.20 mmol) were reacted in the same

manner as for the synthesis of 15 above to yield 0.12 g of the title

complex as a yellow crystalline solid, yield 46.0%. Due to the

appreciable solubility of the product in pentane, a significant amount

remained in the filtrate, resulting in a low isolated yield. An NMR-

scale reaction indicates the formation of the compound in quantitative

yield. Two diastereomers are formed in a 3.3:1 ratio. ¹H NMR (C₆D₆,

23 °C) for diastereomer A (77%): δ 2.01 (s, 3 H, Me₄C₅), 1.72 (s, 3

H, Me₄C₅), 1.61 (s, 3 H, Me₄C₅), 1.20 (s, 3 H, Me₄C₅), 0.93 (s, 9 H,

^tBu-N), 0.75 (d, br, 3 H, Ti-CH₃), 0.21 (s, 3 H, SiMe₂), 0.06 (s, 3 H,

SiMe₂). Diastereomer B (23%): δ 1.76 (s, 3 H, Me₄C₅), 1.65 (s, 3 H,

br, Al-F), -133.31 (s, br, Al-F), -134.08 (m), -138.56 (m), -139.54

3

(m), -153.55 (m), -154.69 (m), -155.08 (m), -161.24 (t, J_F-F

)

3

18.0 Hz), -162.98 (t, J_F-F) 26.1 Hz).

Ethylene, Propylene, Styrene, and Methyl Methacrylate (MMA)

Polymerization Experiments. Ethylene, propylene, styrene, and MMA

polymerizations were carried out at the indicated temperatures in a 250-

mL flamed, round-bottom flask equipped with a magnetic stirring bar,

a thermocouple probe (Omega type K stainless steel sheathed thermo-

couple interfaced to a model HH21 micropressor thermometer), and

attached to the high-vacuum line (see Supporting Information for a

diagram of the reaction vessel). In a typical experiment, a solution of

a cationic complex or a 1:1 ratio of metallocene/cocatalyst in 2 mL of

toluene or 1,2-difluorobenzene (for those catalysts activated with

Ph₃C⁺B(C₆F₅)₄^-), freshly prepared in the glovebox, was quickly injected

(using a gastight syringe equipped with a spraying needle) into a rapidly

stirred flask containing a measured quantity of dry toluene which was

presaturated under 1.0 atm of rigorously purified ethylene or propylene

(pressure control by means of a mercury bubbler) and equilibrated at

the desired reaction temperature using an external constant-temperature

bath. For styrene and MMA polymerizations, the catalyst solution was

quickly injected into a rapidly stirred toluene solution containing 2.0

mL of freshly distilled styrene or MMA under 1.0 atm of Ar.

Preactivation time when generating the catalytically active species in

situ varied with the nature of the cocatalyst, ranging from 8 min for

t

Me₄C₅), 1.57 (s, 3 H, Me₄C₅), 1.17 (s, 3 H, Me₄C₅), 0.96 (s, 9 H, -

Bu-N), 0.79 (d, br, 3 H, Ti-CH₃), 0.31 (s, 3 H, SiMe₂), 0.09 (s, 3 H,

SiMe₂). ¹⁹F NMR (C₇D₈, 23 °C): δ -108.57 (s, br), -113.80 (s, br),

-114.31 (m), -115.30 (s, br), -133.40 (t, ³J_F-F) 16.9 Hz), -137.92

(s, br, Al-F), -138.37 (s, br), -138.56 (s, br, Al-F), -138.94 (t,

³J_F-F) 21.4 Hz), -152.49 (d, ³J_F-F) 21.4 Hz), -152.89 (m), -153.04

(m), -153.27 (m), -154.30 (t, ³J_F-F) 24.5 Hz), -161.05 (m), -162.81

3

(t, J_F-F) 21.4 Hz). ¹³C NMR (C₇D₈, 23 °C): δ 132.30 (Me₄C₅),

128.84 (Me₄C₅), 127.15 (Me₄C₅), 126.95 (Me₄C₅), 126.63 (Me₄C₅),

61.99, 60.50 (Ti-CH₃), 32.85 (N-CMe₃), 15.49 (Me₄C₅), 14.22

(Me₄C₅), 11.97 (Me₄C₅), 10.32 (Me₄C₅), 5.58 (SiMe₂), 4.37 (SiMe₂).

Anal. Calcd for C₅₂H₃₀AlF₂₈NSiTi: C, 47.91; H, 2.32; N, 1.07.

Found: C, 47.47; H, 1.96; N, 0.87.

Synthesis of rac-Me₂Si(Ind)₂ZrMe⁺PBA^-(21). rac-Me₂Si-

(Ind)₂ZrMe₂(0.082 g, 0.20 mmol) and Ph₃C⁺PBA^-(0.261, 0.20 mmol)

were reacted in the same manner as for the synthesis of 15 above to

yield 0.19 g of the title complex as an orange crystalline solid, yield

68.6%. Two diastereomers are found in a 1.3:1 ratio. ¹H NMR (C₆D₆,

23 °C) for diastereomer A (56%): δ 7.45 (d, J_H-H) 8.7 Hz, 1 H,

C₆H₄), 7.27-6.88 (m, 4 H, C₆H₄), 6.67 (t, J_H-H) 7.5 Hz, 2 H, C₆H₄),

5.88 (t, J_H-H) 7.5 Hz, 1 H, C₆H₄), 6.82 (d, J_H-H) 3.3 Hz, 1 H,

C₅H₂), 5.96 (d, J_H-H) 3.3 Hz, 1 H, C₅H₂), 5.69 (s, br, 1 H, C₅H₂),

5.19 (d, J_H-H) 3.3 Hz, 1 H, C₅H₂), 0.43 (s, 3 H, SiMe₂), 0.18 (s, 3 H,

SiMe₂), -0.51 (d, J_H-F) 2.1 Hz, 3 H, Zr-CH₃). Diastereomer B

(44%): δ 7.94 (d, J_H-H) 8.7 Hz, 1 H, C₆H₄), 7.27-6.88 (m, 4 H,

C₆H₄), 6.58 (t, J_H-H) 7.5 Hz, 2 H, C₆H₄), 5.79 (t, J_H-H) 7.5 Hz, 1

H, C₆H₄), 6.42 (d, J_H-H) 3.3 Hz, 1 H, C₅H₂), 5.85 (d, J_H-H) 3.3 Hz,

1 H, C₅H₂), 5.56 (s, br, 1 H, C₅H₂), 4.80 (d, J_H-H) 3.3 Hz, 1 H,

Ph₃C⁺B(C₆F₅)₄and Ph₃C⁺PBA^-, 8 min for B(C₆F₅)₃, to 60 min for

-

PBB. After a measured reaction time interval (kept short to minimize

mass transport and exotherm effects), the polymerization was quenched

by the addition of 2% acidified methanol. The polymer precipitated

by the addition of additional 30 mL of methanol was then collected by

filtration, washed with methanol, and dried on the high-vacuum line

overnight to a constant weight. Reproducibility between runs was

∼10-15% for 2-3 trials per run, and in no case was a polymerization

exotherm greater than 7 °C noted (in room-temperature experiments

they were in the 1.5-4.1 °C range).

Ethylene/1-Hexene and Ethylene/Styrene Copolymerization Ex-

periments. On the high-vacuum line, toluene (23 mL) was condensed

into a flamed, 100-mL reaction flask equipped with a magnetic stirring

bar and a septum-covered sidearm. The solvent was then saturated

with 1.0 atm ethylene, 5.5 mL of 1-hexene or 5.0 mL of styrene was

added by syringe, and the mixture equilibrated at the desired temperature

using an external temperature bath. In the glovebox, 6 mL sample

vials equipped with septum caps were loaded with the cationic

C₅H₂), 0.46 (s, 3 H, SiMe₂), 0.25 (s, 3 H, SiMe₂), -0.64 (d, J_H-F

)

2.1 Hz, 3 H, Zr-CH₃). ¹⁹F NMR (C₆D₆, 23 °C): for diastereomer A

(56%): δ -115.86 (s, br, 3 F), -132.23 (s, br, 1 F, Al-F), -133.76

3

(t, J_F-F) 18.3 Hz, 3 F), -138.53 (s, br, 3 F), -139.40 (t, J_F-F

)

18.3 Hz, 3 F), -153.10 (t, ³J_F-F) 18.3 Hz, 3 F), -153.44 (t, ³J_F-F

18.3 Hz, 3 F), -154.72 (t, ³J_F-F) 21.2 Hz, 3 F), -161.18 (t, ³J_F-F

complexes (25 µmol) or a 1:1 ratio of metallocene/cocatalyst. A

3

18.3 Hz, 3 F), -162.86 (t, J_F-F) 18.3 Hz, 3 F). Diastereomer B

(44%): δ -113.48 (s, br, 3 F), -133.76 (t, J_F-F) 21.2 Hz, 3 F),

measured amount of toluene (2 mL) was then syringed into the vials

containing the above solutions with a dry, Ar-purged gastight syringe.

The vials were removed from the glovebox immediatedly prior to the

copolymerization studies. Each catalyst solution was then syringed

into a reaction flask attached on the high-vacuum line through the

septum-sealed sidearm. The ethylene pressure was kept constant during

the polymerization. After a measured time interval with rapid stirring,

the copolymerization was quenched by the addition of 2% acidified

methanol. The precipitated polymer after the addition of additional

30 mL methanol was then collected by decantation, washed three times

with methanol, and dried on the high-vacuum line overnight.

X-ray Crystallographic Studies of Complexes 3, 13, 14, 19, and

21. Suitable crystals for diffraction studies were grown by slow

diffusion of pentane into a saturated toluene solution of each complex

(3, 13, 19, and 21) in a Cryotrol refrigeration unit (2-propanol cooling

bath with a cooling rate of 10 °C/day and temperature range from 25

°C to -60 °C), or by slow cooling of a saturated methylene chloride/

pentane solution to -20 °C (14). Red crystals of complex 13 were

3

-134.44 (s, br, 1 F, Al-F), -137.89 (s, br, 3 F), -139.09 (t, ³J_F-F

18.3 Hz, 3 F), -153.10 (t, ³J_F-F) 18.3 Hz, 3 F), -153.28 (t, ³J_F-F

18.3 Hz, 3 F), -153.73 (t, ³J_F-F) 18.3 Hz, 3 F), -161.03 (t, ³J_F-F

)

18.3 Hz, 3 F), -162.68 (t, ³J_F-F) 18.3 Hz, 3 F). ¹³C NMR (C₆D₆, 23

°C): δ 134.02, 132.96, 132.43, 128.31, 127.67, 127.28, 126.95, 126.64,

126.21, 125.90, 125.81, 124.88, 124.20, 124.10, 123.57, 122.89, 122.01,

121.98 (C₆-ring), 119.16, 116.56, 115.96, 114.94, 112.90, 112.79 (C₅-

ring), 91.82, 90.95, 89.30, 89.20 (C₅-Si), 51.46, 51.73 (Zr-CH₃),

-1.31, -2.13, -2.88, -3.51 (SiMe₂). Anal. Calcd for C₅₇H₂₁AlF₂₈-

SiZr: C, 49.47; H, 1.53. Found: C, 49.09; H, 1.27.

In Situ Generation of Me₂C(Flu)(Cp)ZrMe⁺PBA^-(22). Me₂C-

(Flu)(Cp)ZrMe₂(3.9 mg, 0.010 mmol) and Ph₃C⁺PBA^-(13.1 mg, 0.010

mmol) were loaded into a J. Young NMR tube and toluene-d₈was

condensed in. The mixture was allowed to react at room temperature

for 0.5 h before the NMR spectrum was recorded. A pair of

diastereomers was formed in a 1.7:1 ratio. The C₆H₄signals of the

Metallocene Polymerization Processes

J. Am. Chem. Soc., Vol. 120, No. 25, 1998 6293

Table 1. Summary of the Crystal Structure Data for Complexes 3, 13, 14, 19, and 21^a

complex

formula

formula weight

crystal color, habit

crystal dimensions (mm)

crystal system

a, Å

3

13

14

19

21

C₆₈H₄₈BF₂₇Zr₂

1571.33

yellow, prismatic

C₈₇H₅₅BF₂₆Zr₂

1787.60

red, platey

C₆₀H₁₅AlF₂₈

1294.72

yellow, platey

C₅₉H₃₀AlF₂₈NSiZr

1431.13

colorless, columnar

C₆₄H₂₉AlF₂₈SiZr

1476.18

yellow, platey

0.60 × 0.30 × 0.08

triclinic

11.884(7)

16.504(7)

17.282(6)

111.99(3)

91.40(4)

93.61(5)

3132(2)

P1h (no. 2)

2

1.565

3.3

ω-θ

2.0-43.9

0.30 × 0.29 × 0.19 0.33 × 0.33 × 0.08

0.40 × 0.20 × 0.08 0.55 × 0.18 × 0.16

monoclinic

11.582(2)

20.997(5)

26.008(5)

triclinic

13.460(4)

15.504(3)

17.568(4)

95.01(1)

91.74(2)

95.65(2)

3631(1)

P1h (no. 2)

2

1.635

4.0

ω-θ

2.0-45.9

triclinic

12.179(5)

12.473(5)

18.334(5)

99.21(3)

94.88(3)

108.82(3)

2574(1)

P1h (no. 2)

2

monoclinic

18.461(9)

13.934(6)

23.85(1)

b, Å

c, Å

R, deg

â, deg

90.72(1)

108.34(4)

γ, deg

V, Å³

6324(1)

P2₁/c (no. 14)

4

1.650

4.5

ω-θ

2.0-46.0

5822(4)

P2₁/c (no. 14)

4

1.632

3.6

ω-θ

2.0-52.0

space group

Z

d (calc), g/cm³

1.670

1.8

ω-θ

2.0-47.9

µ, cm^-1

scan type

2θ range, deg

intensities (unique, R_i)

transmission factor range

secondary extinction

intensities > 2.5σ (I)

> 3.0σ (I)

9297 (9147, 0.046) 10591 (10082, 0.051) 8343 (8057, 0.088) 12225 (12068, 0.089) 8130 (7673, 0.036)

0.8829-0.9202

3.3160e-08

5502

0.8840-0.9687

0.9604-0.9834

0.9186-0.9486

8.47714e-08

4445

0.8449-0.9745

8.48173e-07

5286

3109

514

0.072

0.053

0.72

4561

614

0.094

0.117

1.38

no. of parameters

R

912

0.048

0.040

877

786

0.060

0.047

0.98

0.071

0.056

0.74

R_w

max density in ∆F map e^-/Å³0.68

^aDiffractomer: Enraf-Nonius, CAD4; temperature for data collection, -120 °C; radiation, graphite monochromated; Mo K_R; λ ) 0.71069 Å.

obtained from a saturated toluene solution of 12 on standing at room

temperature for 2 weeks. In each case, the solvent was decanted in

the glovebox, and the crystals were quickly covered with a layer of

Paratone-N oil (Exxon, dried and degassed at 120 °C/10^-6Torr for 24

h). The crystals were then mounted on thin glass fibers and transferred

into the cold-steam (-120 °C) of the Enraf-Nonius CAD4 diffracto-

meter. Final cell dimensions were obtained by a least-squares fit to

the automatically centered settings for 25 reflections. Intensity data

were all corrected for absorption, anomalous dispersion, and Lorentz

and polarization effects. The space group choice for each complex

was determined by statistical analysis of intensity distribution data and

sucessful refinement of the proposed structure. The space groups for

complexes 3 and 17 were determined unambiguously from systematic

absences. Crystallographic data are summarized in Table 1. All

structures were solved by direct methods²⁵and expanded using Fourier

techniques,²⁶and all calculations were performed using the TEXSAN

crystallographic software package of Molecular Structure Corporation.

In complex 3, the non-hydrogen atoms were refined anisotropically

and hydrogen atoms on the Zr cation were refined isotropically with

group thermal parameters. The remaining hydrogen atoms were

included in fixed positions. In complex 13, the phenyl carbon atoms

of the anion, methyl carbon atoms of the cation bridges, and all toluene

carbon atoms were refined isotropically due to the paucity of data, while

all other non-hydrogen atoms were refined anisotropically. Two toluene

molecules were found in the crystal lattice, one of which was found to

be disordered over two positions, each of which was included at half

occupancy. The distances of ring carbons in the disordered toluene

were constrained. Hydrogen atoms were included in idealized positions

except for those on the disordered toluene molecule. In complex 14,

owing to the paucity of data, the carbon atoms were refined isotropically

while the remaining non-hydrogen atoms were refined anisotropically,

and hydrogen atoms were included in idealized positions but not refined.

The carbon atoms of the disordered pentane molecule were fixed to

half occupancy. In complex 19, the disordered toluene carbon atoms

were refined isotropically while the ramaining non-hydrogen atoms were

refined anisotropically. Hydrogen atoms were included in idealized

positions but were not refined, and they were not included in the

structure factors for the disordered toluene. In complex 21, the carbon

atoms of the aluminum anion were refined isotropically. The disordered

toluene atoms were found from the difference map and placed at half

occupancy, but were not refined, while the remaining non-hydrogen

atoms were refined anisotropically. Hydrogen atoms were included

in fixed positions except around the disordered toluene, but were not

refined.

The final cycles of full-matrix least-squares refinement were based

on 5502, 5286, 3109, 4445, and 4561 observed reflections (I > 2.50,

2.50, 3.00, 2.50, and 3.00 σ(I)) and 912, 877, 514, 786, and 614 variable

parameters, and converged (largest parameter shifts were 0.13, 0.61,

0.16, 0.06, and 0.28 times the esd) with unweighted and weighted

agreement factors of R(F) ) 0.048, R_w(F) ) 0.040; R(F) ) 0.060,

R_w(F) ) 0.047; R(F) ) 0.072, R_w(F) ) 0.053; R(F) ) 0.071, R_w(F)

) 0.056; and R(F) ) 0.094, R_w(F) ) 0.117, for 3, 13, 14, 19, and 21,

respectively.

Results and Discussion

I. Borane Cocatalyst PBB. A. Synthesis of PBB. PBB

was synthesized as colorless microcrystals (or faint yellow

crystals depending on the purification method) in 91% yield

from 2-bromononafluorobiphenyl²³which was prepared directly

from C₆F₅Br using an improved synthesis (see Experimental

Section) in 83% yield (Scheme 1). Choice of solvent for the

reaction of 2-nonafluorobiphenyllithium with BCl₃is notewor-

thy. The reaction in pentane from -78 °C to room temperature

afforded a mixture of boranes BCl_xAr^F

(x ) 0-2) which

3-x

proved difficult to separate and purify. The same reaction in

diethyl ether is also not clean and produces a mixture of

products. However, in a 1:1 ratio of pentane/diethyl ether from

-78 °C to room temperature, the above reaction yields the

desired PBB product in 91% yield. Using a 4:1 ratio of the

lithium reagent/BCl₃in ether failed to generate the correspond-

ing tetrakis derivative without the formation of many other

products.

(25) Sheldrick, G. M. SHELXS-86. In Crystallographic Computing;

Sheldrick, G. M., Kruger, C., Goddard, R., Eds.; Oxford University Press:

Oxford, 1985; pp 175-189.

(26) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de

Gelder, R.; Israel, R.; Smits, J. M. M. M. DIRDIF 94. The DIRDIF-94

program system, Technical Report of the Crystallography Laboratory,

University of Nijmegen, The Netherlands, 1994.

B. Metallocene Cations Generated from PBB. Reaction

of PBB with group 4 and Th metallocene dimethyls proceeds

6294 J. Am. Chem. Soc., Vol. 120, No. 25, 1998

Chen et al.

Scheme 1

be isolated in a pure state (with a single exception^1g) for

B(C₆F₅)₃, Ph₃C⁺B(C₆F₅)₄^-, and Bu₃NH⁺B(C₆F₅)₄activated

metallocene systems. The present enhanced stability of µ-Me

bonding likely reflects reduced coordinative tendencies of bulky

MePBB^-vs MeB(C₆F₅)₃^-and the neutral LL′MMe₂precursors,

which exhibit a greater affinity for the cation than does

MePBB^-. For dinuclear cationic complex 6, remarkably only

one of the two possible diastereomers is formed selectively

(possibly B).²⁴On the other hand, two diastereomers are formed

in much closer ratios of 2:1 and 1.8:1 for complexes 9 and 10

(e.g., C and D), respectively. Further discussion regarding the

formation and properties of such dinuclear species is presented

in Section III.

n

-

cleanly to yield cationic complexes (eq 2), which can be isolated

C. Thermal Stability of Monomeric and Dinuclear

Cations. It was found previously that the thermal stability of

MeB(C₆F₅)₃^--based cationic metallocene complexes is very

sensitive to the Cp ancillary ligand substituents.^1hIn compari-

son, complexes 1-10 all exhibit moderate thermal stability and

are stable without noticeable decomposition up to 20 h at room

temperature under an inert atmosphere as toluene or benzene

solutions. However, a solution of complex 3 undergoes

decomposition upon standing at 25 °C over the course of 4 days

or at 80 °C for 1 h to yield [(Cp′′₂ZrMe)₂(µ-F)]⁺MePBB^-(11)

(eq 3), which was characterized both spectroscopically and

and characterized by standard ¹H/¹³C/¹⁹F NMR, analytical

techniques, and X-ray single-crystal diffraction (for complex

3). Except for Cp′₂ThMe₂, CGCZrMe₂, Cp′MMe₃(M ) Ti,

Zr, Hf), the reaction of PBB with all other metallocene dimethyls

having various symmetries (C_2V, C₂, or C_s) forms cationic

dimeric, µ-Me complexes, even with excess PBB and long

reaction times. The ¹³C NMR spectra of complexes 1-10

exhibit downfield M⁺-¹³CH₃resonances characteristic of

“cationic” complexes,^1,2while ¹⁹F spectra exhibit nine, high-

field shifted resonances vs PBB (which exhibits seven), indica-

tive of the formation of anionic MePBB^-with restricted internal

C₆F₄-C₆F₅rotation. Cp′₂ThMe⁺MePBB^-(1) exhibits even

further downfield shifted Th⁺-Me resonances at δ 0.62 ppm

(¹H), 79.28 ppm (¹³C) in C₆D₆than those in Cp′₂ThMe⁺B(C₆F₅)₄^-

(δ 0.34 ppm (¹H), 77.27 ppm (¹³C))^5bin the same NMR solvent,

indicative of highly electron-deficient Th metal centers in both

analytically as well as in a scale-up synthesis in toluene. Such

-

a fluoride-bridged dimeric complex with the MeB(C₆F₅)₃

counteranion was previously obtained in a similar fashion and

was crystallographically characterized.^1hTwo reasonable mech-

anisms accounting for the formation of such complex have also

been proposed:^1h(a) the first involves the transfer of an aryl

ring to the zirconium metal center to form Cp′′₂ZrMe(C₆F₅) and

subsequent fluoride transfer results in the formation of Cp′′₂-

1

complexes. The large J_C-H) 134.3 Hz value for bridging

CH₃groups (complexes 2-4, 6, 9, and 10) is characteristic of

electron-deficient µ-alkyls.^5b,27The crystal structure of complex

3 confirms this assignment and is discussed in section IV.

Bridged µ-Me dinuclear cationic species have been detected

previously in metallocenium NMR studies^1g,5b,7cbut could not

ZrMeF which further reacts with Cp′′₂ZrMe⁺MeB(C₆F₅)₃to

-

form [(Cp′′₂ZrMe)₂(µ-F)]⁺MeB(C₆F₅)₃^-, (b) the second con-

ceivable mechanism involves a direct abstraction of a fluoride

from the MeB(C₆F₅)₃^-anion by the zirconium cation. Interest-

ingly, a third process (aryl abstraction) was found to participate

in a decomposition pathway. When a toluene solution of

(27) (a) Ozawa, F.; Park, J. W.; Mackenzie, P. B.; Schaefer, W. P.;

Henling, L. M.; Grubbs, R. H. J. Am. Chem. Soc. 1989, 111, 1319-1327.

(b) Holton, J.; Lappert, M. F.; Pearce, R.; Yarrow, P. I. W. Chem. ReV.

1983, 83, 135-201 and references therein.

Metallocene Polymerization Processes

J. Am. Chem. Soc., Vol. 120, No. 25, 1998 6295

complex Me₂C(Flu)(Cp)ZrMe⁺MeB(C₆F₅)₃^-(12) was left stand-

ing at room temperature under an inert atmosphere for two

weeks, red crystals formed. An X-ray crystallographic study

(see Section IV) reveals formation of an unusual dimeric

complex, 13 (eq 4), which can be viewed as an adduct between

Me₂C(Flu)(Cp)Zr(C₆F₅)⁺MeB(C₆F₅)₃^-, a product of fluoroaryl

transfer followed by methide abstraction (dissociation and

recombination between Me₂C(Flu)(Cp)Zr(C₆F₅)Me and 12), and

Me₂C(Flu)(Cp)Zr(C₆F₅)F, a product of fluoroaryl transfer and

fluoride abstraction. Such aryl transfer and fluoride abstraction

processes have been observed for similar systems previously;^1b,h,28

however, a decomposition product that involves a combination

of these two processes plus methide abstraction is unprec-

edented.

Probably the most unstable species in this series is the one

generated by reaction of Cp′TiMe₃and PBB. ¹H NMR scale

reactions of Cp′TiMe₃and PBB in CD₂Cl₂revealed evolution

of 1 equiv of CH₄(s, δ 0.21 ppm; δ 0.15 ppm in C₆D₆),

generation of the MePBB^-anion (δ -1.57 ppm, br s), a Ti⁺-

Me functionality (s, δ 1.47 ppm), and many other resonances

around δ 2 ppm. This result suggests an intramolecular C-H

activation/decomposition pathway for this single-ring species

(e.g., Scheme 2). Formation of such intramolecularly metalated

Figure 1. Perspective ORTEP drawing of the molecular structure of

the anion component of the cocatalyst reagent Ph₃C⁺PBA^-(14).

Thermal ellipsoids are drawn at the 50% probability level.

Scheme 3

Scheme 2

characteristics, the synthesis of an aluminum analogue of PBB

using the perfluorobiphenyl ligand was attempted. Under a

variety of conditions, reaction of 2-nonafluorobiphenyllithium

with AlCl₃leads to a compound having the composition

Li⁺(C₁₂F₉)₃AlF^-, which presumably results from aryl fluoride

activation by strongly Lewis acidic, transient “tris(perfluorobi-

phenyl)aluminum” (Scheme 3). Ion exchange metathesis with

Ph₃CCl yields the corresponding trityl (perfluorobiphenyl)-

fluoroaluminate, Ph₃C⁺PBA^-(14), which was characterized by

standard spectroscopic and analytical techniques, as well as by

single-crystal X-ray diffraction (Figure 1), revealing unassoci-

ated trityl cations and sterically congested chiral (C₃-symmetric)

fluoroarylaluminate anions. Further structural discussion is

presented in Section IV. Thermal stability of such aluminum

fluoroaryl species is often a major issue of concern because of

the explosive nature reported in the literature.²⁹For this reason,

thermogravimetric analysis studies of 14 were carried out and

the results compared to those with the borate cocatalyst

Ph₃C⁺B(C₆F₅)₄^-. As can be seen from Figure 2, while total

weight loss occurs near 300 °C for Ph₃C⁺B(C₆F₅)₄^-, there is

only 50% weight loss for Ph₃C⁺PBA^-by 300 °C, indicative of

greater thermal stability.

fulvene-type cationic complexes (C-H activation products, e.g.,

E) has been observed previously and complexes have been

isolated in the case of CGC dibenzyl precursors.²⁴However,

the corresponding scale-up reaction of Cp′TiMe₃and PBB

resulted in the formation of a mixture of unindentified species.

Despite the complexity of this reaction, it was found that the

active species generated by in situ reaction is a very effective

agent for highly syndiospecific styrene polymerization (vide

infra).

B. Metallocene Cations Generated Using Ph₃C⁺PBA^-.

Reaction of Ph₃C⁺PBA^-with metallocene dialkyls in toluene

(28) Scollard, J. D.; McConville, D. H.; Rettig, S. J. Organometallics

1997, 16, 1810-1812.

(29) (a) Spence, R. Chem. Eng. News 1996, 74 (21), 4. (b) Hendershot,

D. G.; Kumar, R.; Barber, M.; Oliver, J. P. Organometallics 1991, 10, 1917.

II. Aluminate Cocatalyst Ph₃C⁺PBA^-. A. Synthesis of

Ph₃C⁺PBA^-. To investigate the properties of other main group

fluoroarylmetals differing in size, shape, and latent ligational

6296 J. Am. Chem. Soc., Vol. 120, No. 25, 1998

Chen et al.

Figure 2. Thermogravimetric analysis (TGA) thermograms of

Ph₃C⁺PBA^-(×) and Ph₃C⁺B(C₆F₅)₄^-(O) cocatalysts at 10 s/point and

3 min/°C temperature ramp.

cleanly generates the corresponding cationic complexes (eq 5)

with NMR and diffraction data (see Section IV for crystal-

lographic discussion) revealing coordination of the PBA^-anion

via M‚‚‚FsAl bridges (e.g., F). The products were character-

1

ized by standard H/¹³C/¹⁹F NMR and analytical techniques.

Crystal structure results are discussed in Section IV.

There are two very interesting features concerning the ion

pairs generated from Ph₃C⁺PBA^-: (a) the bridging ¹⁹F-Al

NMR chemical shifts are extremely sensitive to the group 4

metal ancillary ligand steric bulk and (b) the strong ion pairing

interplay of the PBA^-chirality with the cation symmetry. With

respect to the former effects, the chemical shifts of the bridging

¹⁹F-Al groups are displaced upfield in the order δ -138.11,

-138.69, -143.38, -144.23, -155.78, and -176.81 ppm, for

complexes 15b, 19, 16, 17, 18, and 14, respectively. These

data suggest varying degrees of M⁺‚‚‚FsAl^-interaction, which

is also confirmed by the molecular structure of 19 (Figure 3),

and which qualitatively appears to diminish with increasing

ancillary ligand steric bulk (the stronger the intereaction, the

further downfield the ¹⁹F-Al shift δ; note that is the 14 free

PBA^-anion). Such interactions can also be correlated with

ethylene polymerization activity (vide infra).

Figure 3. Perspective ORTEP drawings of the molecular structure of

the complex CGCZrCH₃⁺PBA^-(19): (A) viewed nearly perpendicular

to the ring Cg-Zr-Cg plane and (B) viewed approximately along the

Al-F-Zr vector. Thermal ellipsoids are drawn at the 50% probability

level.

axes. Some of the representative ¹⁹F NMR spectra for 14, 15a,

and 21 are depicted in Figure 4. The interplay of anion PBA^-

chirality and cation stereochemistry is discussed in detail in

Section III.

III. Solution Molecular Dynamics of Cationic Complexes.

A. Weakly Coordinating Features of the MePBB^-Anion.

Evidence that the MePBB^--metallocenium cation interactions

-

are considerably weaker than those involving MeB(C₆F₅)₃

derives from several lines of argument. First, the CH₃¹H NMR

chemical shift for the MeB(C₆F₅)₃^-anion is rather sensitive to

the metallocene cation counterpart because of varying degrees

The ion pairing interplay of PBA^-chirality and cation

stereochemistry is also evident in the NMR spectra. In contrast

to the seven fluoroaryl ¹⁹F signals observed in free Ph₃C⁺PBA^-,

cationic complexes 15-18 exhibit nine signals (plus one for

the bridging F signal), and complexes 18-22 exhibit an even

greater number, indicative of restricted internal fluoroaryl ring

rotation but free anion rotation (at 25 °C) about the M⁺‚‚‚FsAl^-

-

of anion coordination.^1h,7Unlike the M⁺‚‚‚H₃CB(C₆F₅)₃

analogues, ¹H chemical shifts for MePBB^-are essentially

invariant to countercation identity. Table 2 lists several such

examples showing that MePBB^{- 1}H δ values are independent

of countercation metal (Th, Zr, Ti), ligand framework (Cp, Cp′′,

Cp′, CGC), and aggregation (monomer or dimer), as long as

Metallocene Polymerization Processes

J. Am. Chem. Soc., Vol. 120, No. 25, 1998 6297

lower coordinating tendency of MePBB^-vs MeB(C₆F₅)₃^-and

the L₂MMe₂precursor, as well as the steric encumberance of

PBB which does not allow abstraction of the bridging Zr-Me-

Zr⁺methyl, the formation of isolable cationic, µ-Me dimeric

complexes is favorable. Indeed, these can be isolated in a pure

state in high yields, even when a 1:1 ratio of dimethylmetal-

locene precursor and PBB is employed. However, dissociation

of 3 can be detected by NMR at high temperatures (eq 9) with

Figure 4. ¹⁹F NMR spectra of the free PBA^-anion (14 in CD₂Cl₂)

and coordinated PBA^-anions (15a and 21 in toluene-d₈). The asterisk

denotes a bridge ¹⁹F-Al signal.

a Van’t Hoff analysis (via NMR integration over a temperature

range) yielding ∆H ) 10.2(2) kcal/mol and ∆S ) 26.3(4) eu

(Figure 5). Furthermore, 2-D DNMR experiments reveal rapid

ZrMe_terminalh ZrMe_bridgeexchange above 25 °C in 3 as well as

rapid exchange with the Zr-Me groups of added Cp′′₂ZrMe₂.

With regard to ion pair structural energetics, we find by solution

titration calorimetry studies³⁰that eq 1 for 5 is 20.5(4) kcal/

mol more exothermic for PBB than for B(C₆F₅)₃and that

complex 5 exhibits no NMR evidence of µ-Me complex

formation. The formation of monomeric species in the case of

5 and several complexes (1, 7, and 8) which have sterically

more accessible metal coordinative spheres (Th, CGCZr, single

ring) likely reflects a balance of coordinative competition of

anion vs neutral metallocene, and the coordinatively more open

features of some electrophilic metal centers. This characteristic

apparently allows coordination of the very bulky MePBB^-anion

through weak, labile fluoraryl ring coordination^1a,has evidenced

Table 2. MePBB^{- 1}H Chemical Shifts (δ ppm) as a Function of

Countercation

complex

C₇D₈

CD₂Cl₂

1

3

5

6

7

-0.95

-0.92

-0.95

-0.94

-0.95

-1.57

-1.58

-1.57

-1.58

the same NMR solvent is used. This is indicative of a weakly

coordinating or noncoordinating. Second, in marked contrast

to MeB(C₆F₅)₃^-ion pairs,^1hthe present anion MeB groups are

NMR exchange nonlabile. ¹³C scrambling between 3 and Cp′′₂-

Zr(¹³CH₃)₂in toluene-d₈distributes the ¹³C labels among

terminal methyl, µ-methyl, and Zr(CH₃)₂groups, while the

MePBB^-methyl remains unscrambled (eq 6; * denotes ¹³C

label). Third, the three MePBB^-C₆F₅-C₆F₄groups are

1

by variable-temperature H (MeB groups are NMR exchange

nonlabile) and ¹⁹F NMR (three MePBB^-C₆F₅-C₆F₄groups

are magnetically equiValent down to -90 °C) studies (vide

supra).

B. Chirality of the PBA^-Anion and Interplay with

Cation Stereochemistry. The chirality of the PBA^-anion

arises from restricted internal C₆F₄-C₆F₅rotation and partially

restricted Al-aryl rotation which is responsible for anion

racemization at higher temperatures. In the C_2V-symmetric

metallocenium cations of 15 and 16 (enantiomers G), anion

dissymmetry renders the Cp ligands diastereotopic (¹H δ 5.45,

5.42 ppm in 15a, δ 5.56, 5.48 ppm in 15b). Broadening and

magnetically equivalent in the¹⁹F spectra of 1, 5, and 7 down

to the lowest accessible temperatures (approximately -90 °C),

also indicative of loose ion pairing. Finally, dynamic NMR

studies of ion pair reorganization/symmetrization in 5 (eq 7)

coalescence of the signals at higher temperatures (∆G^‡

)

55°C

16.4(2) kcal/mol in 15b) can be associated with anion stereo-

mutation. With diastereotopic 1,2-Me₂Cp substitution, 16

yield ∆G^‡(40 °C) ) 16.7(3) kcal/mol vs ∆G^‡(40 °C) ) 19.3-

(4) kcal/mol for the MeB(C₆F₅)₃^-analogue,^17aagain suggesting

looser MePBB^-ion pairing.

Several other features of PBB and MePBB^-related chemistry

are also distinctive. A previous study of CGCTiR⁺reactivity²⁴

demonstrated that the relative coordinative tendency of the

fluoroaryl anions/neutral CGCTiMe₂with respect to the CGC-

TiMe⁺cation follows the order MeB(C₆F₅)₃^-> CGCTiMe₂>

MePBB^-, B(C₆F₅)₄^-. Likewise, for Cp′′₂ZrMe⁺paired with

exhibits four Cp Me signals at 25 °C, indicating dissymmetry

with respect to the Cp(centroid)-Zr-Cp(centroid) plane and

that perpendicular (cf., G). On raising the temperature,

broadening and collapse of this pattern to two Me signals is

observed, with ∆G^‡_58°C) 16.9(2) kcal/mol. A barrier compa-

-

the MeB(C₆F₅)₃counteranion, anion coordination is stronger

than the binding of Cp′′₂ZrMe₂, and a µ-Me dimetallic complex

is not detected, except when a large excess of neutral metal-

locene dimethyl is employed (eq 8).^1b,7cHowever, due to the

(30) Luo, L.; Chen, Y.-X.; Marks, T. J., thermochemical research in

progress.

6298 J. Am. Chem. Soc., Vol. 120, No. 25, 1998

Chen et al.

Figure 5. Van’t Hoff plot for dimer-monomer equilibrium in complex

[(Cp′′₂ZrMe)₂(µ-Me)]⁺MePBB^-(3).

rable to that in 15b (suggesting anion racemization) and the

lack of significant additional symmetrization (∆G^‡_87°C> 19.9-

(3) kcal/mol for additional ring Me exchange) argues anion

dissociation/recombination has a significantly higher barrier in

these systems than in analogous metallocenium fluoroarylborates

not having M‚‚‚FsAl coordination (Scheme 4).^1b,hIndeed,

Scheme 4

complexes 19, 20, 21, and 22 each exist in toluene-d₈solution

as pairs of unequally populated (see Experimental Section for

ratios) diastereomers (H, H, I, and J, respectively; enantiomers

not shown) which undergo spectroscopic exchange (∆G^‡

15.8(2) kcal/mol for 19) without permutation of diastereotopic

Cp′′Me groups in 19 and 20 (∆G^‡> 20.5(4) kcal/mol for 19)

or indenyl fragments in 21 (∆G^‡> 20.8(4) kcal/mol).

)

49°C

Figure 6. Perspective ORTEP drawings of the molecular structure of

the complex [(Cp′′₂ZrMe)₂(µ-Me)]⁺MePBB^-(3): (A) cation and (B)

anion. Thermal ellipsoids are drawn at the 50% probability level.

IV. Crystal Structures of Cationic Complexes 3, 13, 14,

19, and 21. A. Cationic Dinuclear Complexes 3 and 13

Derived from Borane Cocatalysts. The solid-state structures

of 3 and 13 as elucidated by single-crystal X-ray diffraction

studies consist of separated, discrete dinuclear [(Cp′′₂ZrMe)₂-

(µ-Me)]⁺and {[Me₂C(Flu)(Cp)Zr(C₆F₅)](µ-F)}⁺cations and

MePBB^-and MeB(C₆F₅)₃^-anions (Figures 6 and 7). Selected

distances and angles for each complex are summarized in Tables

3 and 4, respectively. As can be seen from Figure 6, the two

Cp′′₂ZrMe fragments in 3 are crystallographically nearly identi-

cal (e.g., Zr1-Cp′′-C(ring) (av) ) 2.518 Å and Zr2-Cp′′-

C(ring) (av) ) 2.510 Å) and they are linked by a nearly linear

Zr1-Me-Zr2 CH₃group (sp², hydrogen atoms were refined

isotropically with group thermal parameters) bridging (e.g.,

Zr1-Me-Zr2 ) 170.9(4)°). The two Zr-CH₃(terminal)

groups are arranged in a staggered geometry, and the distances

are significantly shorter than the Zr-CH₃(bridging) distances.

Although one of the Zr-CH₃(bridging) distances appears to

be slightly longer than the other (e.g., Zr1-C1 ) 2.439(8) Å

versus Zr2-C1 ) 2.409 (9) Å), the two Zr-CH₃(terminal)

distances are similar (Zr1-C2 ) 2.235(8) Å, Zr2-C17 ) 2.247-

(9) Å) and shorter than the corresponding distance in

Me⁺MeB(C₆F₅)₃^-can be rationalized in terms of the electronic

characteristics of the metal center (the steric bulk of the ancillary

ligands is equivalent in this case); i.e., more electron-deficient/

coordinatively unsaturated metal centers are accompanied by

stronger Zr-CH₃bonding (shorter Zr-CH₃distances). This

observation supports and elaborates upon earlier results showing

that neutral metallocene dimethyls are less coordinating/electron-

-

donating than the MeB(C₆F₅)₃counteranion as well as olefin

polymerization activity differences (vide infra). The separated

anion MePBB^-framework features substantial twisting of the

C₆F₅-C₆F₄dihedral angles from coplanarity (102° (av)) and

approximately tetrahedral C-B-C valence angles. The average

B-C(aryl) distance of 1.682 Å and B-CH₃of 1.631(9) Å are

comparable to those in a structurally characterized example of

a noncoordinated MeB(C₆F₅)₃^-anion (e.g., B-C (av) ) 1.665

Å and B-CH₃) 1.638(5) Å in [(Cp′′₂ZrMe)₂(µ-F)]⁺MeB-

(C₆F₅)₃^-).^1hAnalysis of the interactions between the cation and

anion components of 3 indicates the closest contacts (C12-F3

) 3.153(8) Å, C19-F13 ) 3.167(9) Å, C28-F27 ) 3.011(9)

Å, C29-F27 ) 3.042(8) Å) between two molecules are through

Cp carbons and aryl fluorine atoms.

Similar to 3, the crystal structure of 13 consists of discrete

and {[Me₂C(Flu)(Cp)Zr(C₆F₅)]₂(µ-F)}⁺cations and MeB(C₆F₅)₃^-

anions. The fluoride-bridged cation has a nearly linear Zr-

-

Cp′′₂ZrMe⁺MeB(C₆F₅)₃(2.252(4) Å).^1hThis shortened Zr-

CH₃(terminal) distance as compared to that in Cp′′₂Zr-

Metallocene Polymerization Processes

J. Am. Chem. Soc., Vol. 120, No. 25, 1998 6299

Table 3. Selected Bond Distances (Å) and Angles (deg) for

[(Cp′′₂ZrMe)₂(µ-Me)]⁺MePBB^-(3)

Bond Distances

Zr1-C1

Zr1-C3

Zr1-C5

Zr1-C7

Zr1-C11

Zr1-C13

Zr2-C1

Zr2-C18

Zr2-C20

Zr2-C22

Zr2-C26

Zr2-C28

B-C32

2.439(8)

2.578(7)

2.525(7)

2.468(7)

2.585(7)

2.439(7)

2.409(9)

2.552(8)

2.490(8)

2.456(9)

2.579(7)

2.461(8)

1.631(9)

1.687(10)

1.507(9)

1.488(9)

1.01(6)

Zr1-C2

Zr1-C4

Zr1-C6

Zr1-C10

Zr1-C12

Zr1-C14

Zr2-C17

Zr2-C19

Zr2-C21

Zr2-C25

Zr2-C27

Zr2-C29

B-C33

2.235(8)

2.590(7)

2.465(7)

2.555(7)

2.506(7)

2.471(7)

2.247(9)

2.571(8)

2.431(9)

2.572(7)

2.467(8)

2.512(8)

1.672(9)

1.686(10)

1.500(10)

1.10(6)

B-C45

B-C57

C38-C39

C62-C63

C1-H1B

C50-C51

C1-H1A

C1-H1C

0.86(6)

Bond Angles

C1-Zr1-C2

Zr1-C1-Zr2

C32-B-C45

C33-B-C45

C45-B-C57

94.3(3)

170.9(4)

108.8(6)

111.4(6)

111.4(5)

C1-Zr2-C17

C32-B-C33

C32-B-C57

C33-B-C57

92.2(3)

110.7(5)

108.6(5)

106.0(5)

Table 4. Selected Bond Distances (Å) and Angles (deg) for

{[Me₂C(Flu)(Cp)Zr(C₆F₅)]₂(µ-F)}⁺MeB(C₆F₅)₃(13)

-

Bond Distances

Zr1-C1

2.418(10)

2.620(9)

2.521(9)

2.453(9)

2.520(9)

2.308(10)

2.402(9)

2.632(9)

2.52(1)

2.435(9)

2.524(10)

2.304(10)

1.64(1)

Zr1-C2

2.513(9)

2.627(9)

2.424(10)

2.436(9)

2.437(10)

2.154(6)

2.536(9)

2.641(10)

2.440(9)

2.526(10)

2.423(10)

2.152(5)

1.68(1)

Zr1-C7

Zr1-C8

Zr1-C13

Zr1-C18

Zr1-C20

Zr1-C22

Zr2-C28

Zr2-C34

Zr2-C40

Zr2-C45

Zr2-C47

Zr2-C49

B-C55

Zr1-C17

Zr1-C19

Zr1-C21

Zr1-F1

Zr2-C29

Zr2-C35

Zr2-C44

Zr2-C46

Zr2-C48

Zr2-F1

B-C56

B-C68

B-C62

Zr1-Flu(cent)

Zr2-Flu(cent)

1.69(1)

1.64(2)

2.16

2.23

Zr1-Cp(cent)

Zr2-Cp(cent)

Figure 7. Perspective ORTEP drawings of the molecular structure of

the complex {[Me₂C(Flu)(Cp)Zr(C₆F₅)]₂(µ-F)}⁺MeB(C₆F₅)₃^-(13): (A)

cation and (B) anion. Thermal ellipsoids are drawn at the 50%

probability level.

Bond Angles

Zr1-F1-Zr2

F1-Zr2-C49

C55-B-C62

C56-B-C62

C62-B-C68

174.3(3) F1-Zr1-C22 105.8(3)

106.9(3) C55-B-C56 102.2(9)

113.3(9) C55-B-C68 118.9(9)

111.2(9) C56-B-C68 114.1(9)

104.5(9)

F-Zr configuration ( Zr1-F-Zr2 ) 174.4(3)°), and the two

fragments are crystallographically virtually equivalent (e.g.,

Zr1-F ) 2.154(6) Å, Zr2-F ) 2.152(5) Å, Zr1-C₆F₅) 2.308-

(10) Å, Zr2-C₆F₅) 2.304(10) Å, Zr1-Flu(cent) ) 2.23 Å,

Zr1-Cp(cent) ) 2.16 Å, Zr2-Flu(cent) ) 2.23 Å, Zr2-Cp-

(cent) ) 2.16 Å, Cp(centroid)-Zr1-Cp(centroid) ) 118.1°, Cp-

(centroid)-Zr2-Cp(centroid) ) 118.0°). The present average

Zr-(µ-F) distance is 2.153(6) Å and is slightly longer than the

corresponding average distance in [(Cp′′₂ZrMe)₂(µ-F)]⁺MeB-

Cp(centroid)-Zr1-Cp(centroid) 118.1

Cp(centroid)-Zr2-Cp(centroid) 118.0

5. In the solid state, fluoroaryl rings are substantially twisted

out of coplanarity (86° (av) ranging from 53 to 104°). In

solution, however, free rotation of the fluoroaryl rings averages

o- and m-arylfluorine and the PBA^-anion exhibits only seven

¹⁹F NMR resonances (plus one broad Al-F signal) at room

temperature. Interestingly, when this anion is coordinated to

an electrophilic metal center, these rotations are restricted in

solution.

-

(C₆F₅)₃(2.113(2) Å).^1hIn the solid state, the unassociated

-

MeB(C₆F₅)₃anion adopts a pseudotetrahedral geometry and

the average B-C(aryl) distance (1.67(1) Å) is comparable to

those in coordinated or free anions.^1hOn the other hand, the

B-CH₃distance (1.64(1) Å) is noticeably shorter than those in

The solid-state structures of PBA^-cation-anion pairs 19 and

21 are shown in Figures 3 and 7, respectively, and important

distances and angles for each complex are summarized in Tables

6 and 7, respectively. The crystal structure of complex 19

reveals CGCZrCH₃⁺cation and PBA^-anion pairing via a nearly

linear Zr‚‚‚FsAl bridge ( Zr-F-Al ) 175.4(4)°) with Zr-F

and Al-F distances of 2.123(6) and 1.780(6) Å, repectively.

The Zr-F distance is considerably longer than the Zr-F

-

coordinated MeB(C₆F₅)₃anions.

B. Aluminate Cocatalyst 14 and Cationic Complexes 19

and 21 Derived Therefrom. The crystal structure of 14

features an unassociated trityl cation and sterically congested

chiral C₃-symmetric (fluoroaryl)fluoroaluminate anion (Figure

1). Selected bond distances and angles are summarized in Table

6300 J. Am. Chem. Soc., Vol. 120, No. 25, 1998

Chen et al.

Table 5. Selected Bond Distances (Å) and Angles (deg) for

Ph₃C⁺PBA^-(14)

Bond Distances

Al-F28

Al-C13

C6-C7

C30-C31

C37-C44

1.682(5)

2.019(10)

1.47(1)

Al-C1

2.027(9)

2.009(9)

1.47(1)

1.44(1)

Al-C25

C18-C19

C37-C38

C37-C50

1.50(1)

1.44(1)

Bond Angles

F28-Al-C1

108.6(3)

105.4(3)

115.9(4)

119.3(9)

121.2(9)

F28-Al-C13

C1-Al-C13

C13-Al-C25

C38-C37-C50

109.0(3)

110.0(4)

107.7(4)

119.6(9)

F28-Al-C25

C1-Al-C25

C38-C37-C44

C44-C37-C50

(terminal) distance in [(Cp′′₂ZrF)₂(µ-F)]⁺B(C₆F₄TBS)₄^-(1.93-

(1) Å)^1band slightly longer than the Zr-F bridging distances

in [(Cp′′₂ZrF)₂(µ-F)]⁺B(C₆F₄TBS)₄^-(2.11(1) Å)^1band in [(Cp′′₂-

-

ZrMe)₂(µ-F)]⁺MeB(C₆F₅)₃(2.113 Å (av)).^1hThe Al-F dis-

tance is also considerably longer than the Al-F distance in

PBA^-(1.682(5) Å), suggesting distinctive cation-anion coor-

+

dination characteristics in complex 19. The CGCZrCH₃

metrical parameters in 19 are similar to those in CGC-

ZrCH₃⁺MeB(C₆F₅)₃^{- 17a}with almost identical Zr-CH₃distances

of 2.21(1) and 2.224(4) Å, Zr-N distances of 2.027(8) and

2.030(3) Å, Si-N distances of 1.733(8) and 1.737(3) Å, and

Cp(centroid)-Zr-N angles of 101.0(4) and 102.5(1)°, respec-

tively, reflecting similar electron-deficient character in both

CGCZrCH₃cations. The large PBA^-anion adopts an ap-

+

proximately tetrahedral geomety with an average Al-C(aryl)

distance (2.00(1) Å) and C₆F₅-C₆F₄dihedral angle (89° (av),

ranging from 68 to 109°) comparable to those in the free PBA^-

anion (2.018 Å and 86° (av)).

Unlike complex 19, which has a nearly linear Zr-F-Al

configuration, the Zr-F28-Al angle in 21 is bent to 166.5-

(8)°. Within the accuracy of the present determination for this

complex, the metrical parameters for 21 suggest a slightly tighter

cation-anion interaction than in 19, as represented by a shorter

Zr-F distance (2.10(1) Å) and a longer Al-F distance (1.81-

(1) Å), while other metric parameters for the anion portion

(average Al-C(aryl) distance ) 2.03(2) Å and average C₆F₅-

C₆F₄dihedral angle ) 89°, ranging from 63 to 100°) are

comparable to those in 19. The rac-Me₂Si(Ind)₂ZrCH₃⁺cation

adopts a normal “bent sandwich” configuration with Cp-

(centroid)-Zr-Cp(centroid) angle of 128.2(1)°, which is not

unexpectedly smaller than the bis-Cp type of nonbridged

metallocene cations.^1hThe Zr-CH₃distance (2.24(2) Å) is also

comparable to those in other metallocene ZrCH₃⁺species which

have been characterized structurally,¹reflecting the cationic

character of 21.

Figure 8. Perspective ORTEP drawings of the molecular structure of

the complex rac-Me₂Si(Ind)₂ZrCH₃⁺PBA^-(21): (A) viewed nearly

perpendicular to the ring Cg-Zr-Cg plane and (B) viewed ap-

proximately along the Al-F-Zr vector. Thermal ellipsoids are drawn

at the 50% probability level.

V. Polymerization Catalysis. A. Polymerization of

Methyl Methacrylate (MMA) by Dinuclear Cationic Com-

plexes. Stereospecific polymerization of MMA has been

achieved to produce both syndiotactic poly(methyl methacrylate)

(syndiotactic PMMA, K) by achiral organolanthanide complexes

anionically initiated polymerizations.³³Unlike neutral organo-

lanthanide complexes which apparently have more tolerance

toward polar monomers than do isoelectronic/cationic group 4

complexes, Cp₂ZrMe⁺MeB(C₆F₅)₃exhibits no conversion of

-

MMA monomer after 6 h of reaction at 0 °C (entry 1, Table 8).

Recently, Soga and co-workers³⁴reported that zirconocene

dimethyl complexes in combination with stoichimetric amounts

of activators such as B(C₆F₅)₃and Ph₃C⁺B(C₆F₅)₄^-, in the

(e.g., C₅Me₅) SmH)₂,³¹and isotactic PMMA (L) by chiral

2

organolanthanide complexes (e.g., (R)-(neomenthyl)LaN(T-

MS)₂),³²at higher polymerization temperatures than typical

(32) Giardello, M. A.; Yamamoto, Y.; Brard, L.; Marks, T. J. J. Am.

Chem. Soc. 1995, 117, 3276.

(33) (a) Hatada, K.; Kitayama, K.; Ute, K. Prog. Polym. Sci. 1988, 13,

189. (b) Aida, T.; Maekawa, Y.; Asano, S.; Inoue, S. Macromolecules 1988,

21, 1195.

(34) (a) Deng, H.; Shiono, T.; Soga, K. Macromolecules 1995, 28, 3067.

(b) Soga, K.; Deng, H.; Yano, T.; Shiono, T. Macromolecules 1994, 27,

7938.

(31) Yasuda, H.; Yamamoto, H.; Yokota, K.; Miyake, S.; Nakamora,

A. J. Am. Chem. Soc. 1992, 114, 4908.

Metallocene Polymerization Processes

J. Am. Chem. Soc., Vol. 120, No. 25, 1998 6301

Table 6. Selected Bond Distances (Å) and Angles (deg) for

CGCZrCH₃⁺PBA^-(19)

9 derived from a C₂-symmetric metallocene precursor and PBB,

highly isotactic PMMA is produced (entry 6). However, in

attempts to produce highly syndiotactic PMMA by using

dinuclear cationic complexes 6 and 10, derived from C_s-

symmetic metallocene precursors, no conversion of monomer

is observed under a variety of polymerization conditions (entries

7-10), reflecting the marked sensitivity of metallocene-mediated

MMA polymerization to the ancillary ligand framework.

Bond Distances

Zr-F1

2.123(6)

2.43(1)

2.55(1)

2.44(1)

1.733(8)

1.89(1)

1.780(6)

1.98(1)

1.48(1)

1.54(1)

Zr-N

2.027(8)

2.48(1)

2.53(1)

2.21(1)

1.89(1)

1.86(1)

2.01(1)

2.00(1)

1.47(1)

1.49(1)

Zr-C1

Zr-C3

Zr-C5

Si-N

Zr-C2

Zr-C4

Zr-C16

Si-C1

Si-C11

Al-C17

Al-C41

C22-C23

C46-C47

Si-C10

Al-F1

Al-C29

N-C12

C34-C35

A plausible mechanism for MMA polymerization mediated

by cationic dinuclear metallocene complexes, modified from

the basic scenario of Collins,³⁵is depicted in Scheme 5. A fast

equilibrium is established in which polar MMA monomer

displaces neutral metallocene Cp₂ZrMe₂from the metallocene

cation to form an adduct M. Slow initiation involves methyl

transfer from Cp₂ZrMe₂to M to form a neutral enolate (N)

which then participates in the propagation process via intermo-

lecular Michael addition to an activated monomer in cationic

M to produce PMMA.

Bond Angles

F1-Zr-N

123.2(3)

106.3(4)

99.8(4)

F1-Zr-C16

F1-Al-C17

F1-Al-C41

C17-Al-C41

Zr-F1-Al

95.6(3)

106.5(4)

99.2(4)

118.9(4)

175.4(4)

123.3(7)

105.0(6)

N-Zr-C16

F1-Al-C29

C17-Al-C29

C29-Al-C41

Zr-N-Si

111.2(5)

117.6(5)

108.7(4)

127.9(7)

91.4(4)

Zr-N-C12

C10-Si-C11

Si-N-C12

N-Si-C1

B. Polymerization of Ethylene by Monomeric and Di-

nuclear Metallocene Cations. Comparison of ethylene po-

lymerization activities of monomeric and dinuclear metallocene

Table 7. Selected Bond Distances (Å) and Angles (deg) for

rac-Me₂Si(Ind)₂ZrCH₃⁺PBA^-(21)

cations having MeB(C₆F₅)₃and MePBB^-counteranions and

-

the properties of the resulting polymers are summarized in Table

9. Despite µ-Me ground-state geometries, the ethylene polym-

erization activities of dinuclear complexes 2-4 rival or exceed

those of the B(C₆F₅)₃analogues, and yield higher molecuar

weight polyethylenes (2 vs 1, 4 vs 3, and 6 vs 5). It is possible

that µ-Me dimer dissociation, hence slower initiation, may be

connected with slightly increased polydispersities. These po-

lymerization results are completely in accord with previous

conclusions from solution phase and solid-state structural studies

that the neutral metallocene dimethyl is a weaker charge-

Bond Distances

Zr-F28

Zr-C2

2.10(1)

2.43(2)

2.58(2)

2.44(2)

2.55(2)

2.53(2)

1.86(2)

1.84(3)

2.04(2)

2.00(2)

1.48(2)

2.230(2)

Zr-C1

2.24(2)

2.56(2)

2.45(2)

2.47(2)

2.63(2)

1.89(2)

1.87(3)

1.81(1)

2.04(2)

1.49(2)

1.54(2)

2.212(2)

Zr-C3

Zr-C9

Zr-C10

Zr-C12

Zr-C14

Si-C10

Si-C20

Al-F28

Al-C34

C27-C28

C51-C52

Zr-Cp(cent2)

Zr-C11

Zr-C13

Zr-C19

Si-C11

Si-C21

Al-C22

Al-C46

C39-C40

Zr-Cp(cent1)

-

compensating agent/donor than the MeB(C₆F₅)₃anion, while

MePBB^-is the least donating in this series.

Bond Angles

90.8(6) C10-Si-C11

C. Olefin Polymerization by “Constrained Geometry”

Catalysts. Table 10 summarizes ethylene polymerization as

well as ethylene-1-hexene and ethylene-styrene copolymeriza-

tion experiments with “constrained geometry” catalysts gener-

ated from B(C₆F₅)₃and PBB. It can be seen from the table

that the effects of ion pairing on “constrained geometry” catalyst

performance are dramatic. While the MeB(C₆F₅)₃^-derivatives

are essentially inactive (M ) Zr, entry 1) or marginally active

(M ) Ti, entry 3) for ethylene polymerization at 25 °C, the

MePBB^-analogues are highly actiVe with rate enhancements

of 10⁵and ∼70 times for the Zr and Ti catalysts, respectiVely

(entries 2 and 4). This trend obtains for the ethylene-1-hexene

and ethylene-styrene copolymerizations as well, with both PBB-

derived catalysts exhibiting comparable comonomer incorpora-

tion with narrower polydispersities at higher polymerization rates

(entries 5-8). The CGCZrCH₃⁺MePBB^-catalyst remarkably

mediates ethylene-1-hexene copolymerization with large quanti-

ties of 1-hexene introduction (33.6%) and with high catalytic

activity (5.58 × 10⁵g of polymer/(mole Zr atm h). These

MeB(C₆F₅)₃^-vs MePBB^-activity differences again doubtless

reflect the relative coordinative tendencies of the anions and

tightness of the ion pairing as well as their important role in

the olefin polymerization process. This significantly amplified

F28-Zr-C1

C20-Si-C21

F28-Al-C34

C22-Al-C34

C34-Al-C46

93.6(9)

114.1(1) F28-Al-C22 101.9(7)

101.7(6) F28-Al-C46 104.1(6)

115.1(8) C22-Al-C46 112.0(8)

119.0(8) Zr-F28-Al

166.5(8)

Cp(centroid)-Zr-Cp(centroid) 128.2(1)

presence of a large excess of dialky zinc, initiate polymerization

of MMA to produce PMMAs with high molecular weights and

narrow molecular weight distributions, however at low polym-

erization rates. Collins and co-workers³⁵have reported that the

cationic zirconocene complex Cp₂ZrMe(THF)⁺BPh₄^-promotes

syndiospecific polymerization of MMA in the presence of excess

neutral zirconocene dimethyl and studied the polymerization

mechanism in detail. To further examine the mechanism and

the function of the neutral zirconocene dimethyl in the polym-

erization process from a different perspective, we investigated

the present isolable, and well-characterized cationic dinuclear

complexes derived from PBB. We find that these binuclear

catalysts are efficient initiators for polymerization of MMA

(entries 2-6, Table 8) to produce syndiotactic PMMA or

isotactic PMMA depending on the symmetry of the initiator.

Raising the polymerization temperature enhances the polym-

erization rate (entry 3 vs 2), while increasing the steric bulk of

the ancillary ligand framework has a significant effect on

enhancing stereoregulation (entries 4 and 5 vs 2). Most

interestingly, by employing chiral dinuclear cationic complex

-

activity difference for the CGC catalysts with the MeB(C₆F₅)₃

and (MePBB)^-anions suggests that anion dimensions will have

the greatest effects on polymerization activity for those sterically

more accessible (coordinatively more open) catalysts, such as

the CGC system.

(35) (a) Li, Y.; Ward, D. G.; Reddy, S. S.; Collins, S. Macromolecules

1997, 30, 1875. (b) Collins, S.; Ward, D. G. J. Am. Chem. Soc. 1992, 114,

5460.

D. Olefin Polymerization Mediated by Mono-Cp (Single-

Ring) Catalysts. The performance of single-ring catalysts in

6302 J. Am. Chem. Soc., Vol. 120, No. 25, 1998

Chen et al.

Table 8. Methyl Methacrylate Polymerization Mediated by Dinuclear Cationic Complexes Derived from PBB^a

tacticity

entry

catalyst^b

T_p(°C)

time (h)

conversion (%)

[mm]

[mr]

[rr]

Cp₂ZrMe⁺MeB(C₆F₅)₃

0

25

0

25

0

6.0

2.5

2.3

8.5

5.5

7.0

3.0

6.0

0

100

46

100

0

-

1

2

3

4

5

6

7

8

9

[(Cp₂ZrMe)₂(µ-Me)]⁺MePBB^-

3.3

3.8

2.9

2.4

93.0

34.3

36.0

29.8

30.0

4.8

62.4

60.2

67.3

67.6

2.2

[(Cp₂ZrMe)₂(µ-Me)]⁺MePBB^-

[(Cp′′₂ZrMe)₂(µ-Me)]⁺MePBB^-

[(Cp′₂ThMe)₂(µ-Me)]⁺MePBB^-

{[rac-Me₂Si(Ind)₂ZrMe]₂(µ-Me)}⁺MePBB^-

[(CGCTiMe)₂(µ-Me)]⁺MePBB^-

[(CGCZrMe)₂(µ-Me)]⁺MePBB^-

{[Me₂C(Cp)(Flu)ZrMe]₂(µ-Me)}⁺MePBB^-

10

25

^aConditions: 20 µmol catalyst; 2.0 mL MMA (18.7 mmol); MMA/cat., mol/mol ) 935; 20 mL toluene; solvent/[M₀] ) 10 vol/vol. ^bCatalysts

(entries 5 and 8) generated by in situ reaction of 2L₂MMe₂+ PBB in 2 mL of toluene for 0.5 h.

Scheme 5

possibly other species.³⁷The Cp′TiMe₃/PBB catalytic system

is also very efficient for ethylene-1-hexene copolymerization.

Under comparable polymerization conditions, the Cp′TiMe₃/

PBB catalyst exhibits considerably higher activity and produces

the copolymer with slightly a higher level of 1-hexene inco-

poration and with much narrower polydispersity than the

Cp′TiMe₃/B(C₆F₅)₃catalyst system (entries 5 and 6).

E. Propylene Polymerization Mediated by C₂- and C_s-

Symmetric Metallocene/B(C₆F₅)₃, PBB, and Ph₃C⁺B(C₆F₅)₄

-

Catalysts. Table 12 summarizes results for both isospecific^3a,20b

and syndiospecific³⁸propylene polymerizations catalyzed by the

present chiral metallocene catalysts. Polymerization conditions

such as catalyst concentrations and polymerization times were

controlled in such a manner that the reaction temperature rise

during the course of polymerization was usually below 4 °C

for the ambient temperature runs, mass transport effects were

minimized, and similar quantities of polymers were produced.

For isospecific propylene polymerization mediated by C₂-

symmetric rac-Me₂Si(Ind)₂ZrMe₂activated with various co-

catalysts (entries 1-6), there is a noticeable activity increase

from B(C₆F₅)₃, to Ph₃C⁺B(C₆F₅)₄^-, to PBB; however, the

isotacticity remains essentially the same, as judged by melting

transition temperature (T_m) and methyl pentad content (mmmm)

of the polymer samples. The same trend is observed for

syndiospecific propylene polymerization mediated by C_s-sym-

metric Me₂C(Flu)(Cp)ZrMe₂/-cocatalyst combinations (entries

7 and 8) with regard to the activity enhancement and the about

same in regard to syndioselection. Therefore, this observation

appears to suggest that polymerization activity can be influenced

substantially by the relative tightness of cation-anion interac-

tion; however, the polymerization stereoselectivity is governed

(in these cases) primarily by the intrinsic characteristics of the

cation (symmetry, sterics, and electronics) and far less by weakly

coordinating anions. However, if anion interaction involves

specific coordinative intrusion into the cation coordination

sphere, the effect on stereoselection can be significant (via infra).

F. Ethylene and Propylene Polymerization by Metallocene/

Ph₃C⁺PBA^-Catalysts. Table 13 summarizes ethylene po-

lymerization (entries 1-8) and propylene polymerization (entries

9 and 10) results for PBA^--based catalysts. There is a

remarkable sensitivity of ethylene polymerization characteristics

to ion pairing as inferred from ancillary ligand bulk, diffraction

styrene and ethylene-1-hexene copolymerization is shown in

Table 11. Despite the complexity of the Cp′TiMe₃/PBB reaction

chemistry (vide supra), the reaction mixture catalyzes rapid

syndiospecific styrene polymerization to produce highly syn-

diotactic polystyrene³⁶with [rrrr] ) 98% (entry 1). On the

other hand, the isolated and characterized M(IV)⁺complexes

of M ) Zr and Hf only catalyze aspecific styrene polymerization

to yield actactic polystyrene (entries 3 and 4), which supports

the hypothesis that the true active species for syndiospecific

styrene polymerization is probably not Ti(IV)⁺, but Ti(III)⁺or

(37) Evidence for the Ti(III)⁺formation in Cp′TiR₃/B(C₆F₅)₃, MAO

catalyst systems (R ) Cl, CH₃, CH₂Ph, OBu) can be found in: (a) Grassi,

A.; Zambelli, A.; Laschi, F. Organometallics 1996, 15, 480-482. (b) Grassi,

A.; Pellecchia, C.; Oliva, L.; Laschi, F. Macromol. Chem. Phys. 1995, 196,

1093-1100. (c) Chien, J. C. W.; Salajka, Z.; Dong, S. Macromolecules

1992, 25, 3199-3203. (d) Bueschges, U.; Chien, J. C. W. J. Polym. Sci.

Polym. Chem. 1989, 27, 1525-1538.

(36) (a) Wang, Q.; Quyoum, R.; Gillis, D. J.; Tudoret, M.-J.; Jeremic,

D.; Hunter, B. K.; Baird, M. C. Organometallics 1996, 15, 693-703. (b)

Ready, T. E.; Day, R. O.; Chien, J. C. W.; Rausch, M. D. Macromolecules

1993, 26, 5822-5823. (c) Pellecchia, C.; Longo, P.; Proto, A.; Zambelli,

A. Makromol. Chem. Rapid Commun. 1992, 13, 265-268. (d) Pellecchia,

C.; Longo, P.; Grassi, A.; Ammendola, P.; Zambelli, A. Makromol. Chem.,

Rapid Commun. 1987, 8, 277-279. (e) Ishihara, N.; Seimiya, T.; Kuramoto,

M.; Uoi, M. Macromolecules 1986, 19, 2465-2466.

(38) Ewen, J. A.; Jones, R. L.; Razavi, A.; Ferrara, J. D. J. Am. Chem.

Soc. 1988, 110, 6255-6256.

Metallocene Polymerization Processes

J. Am. Chem. Soc., Vol. 120, No. 25, 1998 6303

Table 9. Comparison of Ethylene Polymerization Activities Mediated by Monomeric and Dinuclear Metallocene Cations Having

Counteranions MeB(C₆F₅)₃^-, MePBB^-, and Polymer Properties^a

µmol

of cat.

reaction

time (s)

polymer

yield (g)

entry

catalyst

activity^b

10^-3M_w

M_w/M_n

-

1

2

3

4

5

6

Cp₂ZrMe⁺MeB(C₆F₅)₃

0.15

60

40

60

40

60

1.0

0.8

1.5

1.3

0.8

1.1

4.0 × 10⁶

4.8 × 10⁶

6.0 × 10⁶

7.8 × 10⁶

3.2 × 10⁶

4.4 × 10⁶

124

559

321

392

136

370

2.03

3.06

1.42

2.72

2.54

2.28

[(Cp₂ZrMe)₂(µ-Me)]⁺MePBB^-

-

Cp′′₂ZrMe⁺MeB(C₆F₅)₃

[(Cp′′₂ZrMe)₂(µ-Me)]⁺MePBB^-

Cp′₂ZrMe⁺MeB(C₆F₅)₃

-

[(Cp′₂ZrMe)₂(µ-Me)]⁺MePBB^-

^aCarried out at 25 °C, 1.0 atm of ethylene, and 100 mL of toluene on a high vacuum line. ^bIn units of grams of polymer/(mole of cat‚atm‚h).

Table 10. Summary of Ethylene Polymerization, Ethylene-1-Hexene, and Ethylene-Styrene Copolymerizations Catalyzed by Constrained

Geometry Catalysts^a

µmol

of cat.

reaction

time (min)

polymer

yield (g)

%comonomer

incorporation

entry

catalyst

monomer

activity^b

10^-3M_w

M_w/M_n

-

1

2

3

4

5

6

7

8

9

CGCZrMe⁺MeB(C₆F₅)₃

CGCZrMe⁺MePBB^-

E

E/H

E/S

15

50

25

20

4

10

4

15

10

15

0

1.60

0.20

0.80

0

6.97

0.05

1.95

0.45

0.80

1.60 × 10⁶

8.00 × 10⁴

5.60 × 10⁶

0

7.69

1058

305

2.78

9.54

2.56

-

CGCTiMe⁺MeB(C₆F₅)₃

(CGCTiMe)₂Me⁺MePBB^-

CGCZrMe⁺MeB(C₆F₅)₃

-

CGCZrMe⁺MePBB^-

5.58 × 10⁵

1.20 × 10⁴

4.68 × 10⁵

7.20 × 10⁴

1.28 × 10⁵

33.6

63.2

65.3

35.2

33.4

10.0

105

2.68

1.86

CGCTiMe⁺MeB(C₆F₅)₃

-

(CGCTiMe)₂Me⁺MePBB^-

CGCTiMe⁺MeB(C₆F₅)₃

-

10

(CGCTiMe)₂Me⁺MePBB^-

^aEthylene (E) polymerizations were carried out at 25 °C, 1 atm ethylene, and 100 mL of toluene on a high-vacuum line; ethylene-1-hexene

(E/H) and ethylene-styrene (E/S) copolymerizations were carried out at 25 °C, 0.356 M of ethylene, 1.78 M of 1-hexene and styrene, and 25 mL

of toluene on a high-vacuum line. ^bIn units of grams of polymer/(mole of cat‚atm‚h).

Table 11. Summary of Styrene Polymerization, Ethylene-1-Hexene, and Ethylene-Styrene Copolymerizations Catalyzed by Mono-Cp

Metallocene Catalysts^a

reaction

time (min)

polymer

yield (g)

entry

catalyst

monomer

activity

10^-3M_w

M_w/M_n

remarks

1

2

3

4

5

6

Cp′TiMe₃-PBB

S

E/H

15

10

15

5.0

0.40

1.51

1.21

0.70

4.51

1.80 × 10⁶

1.01 × 10⁷

5.51 × 10⁶

3.20 × 10⁶

1.70 × 10⁵

1.08 × 10⁶

170

2.56

[rrrr] ) 98%

atactic

%H ) 39.5

%H ) 43.6

Cp′ZrMe₂⁺MePBB^-

Cp′HfMe₂⁺MePBB^-

Cp′HfMe₃-B(C₆F₅)₃

Cp′TiMe₃-B(C₆F₅)₃

Cp′TiMe₃-PBB

22.9

24.8

848

2.78

2.98

23.7

4.32

151

^aStyrene (S) polymerizations (entries 1-4) were carried out at 25 °C, 2.0 mL (17.4 mmol) of styrene, 50 µmol of catalyst, and 5 mL of toluene

on high-vacuum line. Titanium catalysts were generated by in situ reaction of Cp′TiMe₃+ borane in 2 mL toluene. Activities in units of gram of

bulk polymer/(mole of cat.)‚(mole of monomer)‚h; ethylene-1-hexene (E/H) copolymerizations (entries 5 and 6) were carried out at at 25 °C, 0.356

M of ethylene, 1.78 M of 1-hexene, 50 µmol of catalyst, and 25 mL of toluene on high-vacuum line.

Table 12. Isospecific and Syndiospecific Propylene Polymerizations Catalyzed by C₂- and C_s-Symmetric Metallocene/B(C₆F₅)₃, PBB, and

Ph₃C⁺B(C₆F₅)₄Catalysts^a

-

[cat.]

reaction

polymer

entry

catalyst

µmol T_p(°C) time (min) yield (g)

activity^b

M_w× 10³M_w/M_nT_m(°C) mmmm%

1

2

3

4

5

6

7

8

Me₂Si(Ind)₂ZrMe₂, B(C₆F₅)₃

Me₂Si(Ind)₂ZrMe₂, Ph₃C⁺B(C₆F₅)₄

Me₂Si(Ind)₂ZrMe₂, PBB

Me₂Si(Ind)₂ZrMe₂, B(C₆F₅)₃

Me₂Si(Ind)₂ZrMe₂, Ph₃C⁺B(C₆F₅)₄

Me₂Si(Ind)₂ZrMe₂, PBB

10

2.0

10

2.0

24

60

24

2.5

4.0

2.0

1.75

1.5

1.0

0.73

0.77

0.62

0.63

0.93

0.53

3.15

3.53

1.8 × 10⁶

5.8 × 10⁶

9.3 × 10⁶

2.2 × 10⁶

19 × 10⁶

16 × 10⁶

2.4 × 10⁵

5.3 × 10⁵

32.6

123

2.40

1.94

1.91

1.39

2.23

2.04

146

147

146

122

127

130

93

86

84

86

77^c

81^c

-

99.2

2.7

41.1

43.6

Me₂C(Cp)(Flu)ZrMe₂, B(C₆F₅)₃

Me₂C(Cp)(Flu)ZrMe₂, PBB

20

40

20

^aAll polymerizations carried out on high-vacuum line in 50 mL of toluene under 1 atm of propylene pressure. ^bGram of polymer/[(mole of

cationic metallocene)‚atm‚h]. ^c%rrrr.

structural data, and NMR δ ¹⁹F-Al values. It can be seen from

the table that while Cp₂ZrCH₃⁺PBA^-and CGCMCH₃⁺PBA^-

exhibit negligible ethylene polymerization activities at 25 °C/

1.0 atm monomer pressure (entries 1, 5, and 6), increasing

ancillary ligand bulk effects dramatic increases in polymerization

activity which roughly parallel trends in δ ¹⁹F-Al values (entries

2-4). Furthermore, CGCMCH₃⁺polymerization characteristics

are markedly temperature-dependent, with CGCTiCH₃⁺PBA^--

mediated polymerization at 60 and 110 °C affording ultrahigh

molecular weight polyethylene (entries 7 and 8). With regard

to anion effects on chiral cation stereoregulation, propylene

polymerization (60 °C, 2 µmol catalyst) mediated by rac-Me₂-

-

Si(Ind)₂ZrMe₂/Ph₃C⁺B(C₆F₅)₄yields products of low isotac-

ticity ([mmmm] ) 84%; Figure 9A), while under similar

polymerization conditions (60 °C, 20 µmol catalyst), the strongly

ion-paired PBA^-analogue 21 produces highly isotactic polypro-

pylene ([mmmm] ) 98%; Figure 9B), albeit with reduced

polymerization activity. As revealed by the X-ray crystal

6304 J. Am. Chem. Soc., Vol. 120, No. 25, 1998

Table 13. Ethylene and Propylene Polymerization Activities Mediated by Metallocene/Ph₃C⁺PBA^-Catalysts and Polymer Properties^a

cat. reaction polymer

Chen et al.

entry

catalyst

monomer T_p(°C) (µmol) time (min) yield (g)

activity^b

M_w

M_W/M_n

remarks

1

2

Cp₂ZrMe₂

Cp′′₂ZrMe₂

E

25

20

30

0

0.18

0

1.80 × 10⁴5.46 × 10⁵

1.08 × 10⁶1.26 × 10⁶

6.90 × 10⁶8.97 × 10⁴

6.0

5.6

4.6

T_m) 139.4 (°C)

∆H_u) 40.5 (cal/g)

T_m) 142.3 (°C)

∆H_u) 29.5 (cal/g)

T_m) 138.0 (°C)

∆H_u) 53.9 (cal/g)

(Cp^TMS) ₂ZrMe₂

E

25

15

2.0

0.67

10

30

0.54

1.15

2

3

4

Cp′₂ZrMe₂

5

6

7

CGCZrMe₂

CGCTiMe₂

E

25

60

15

30

0

0.20

0

1.33 × 10⁴2.05 × 10⁶

3.9

3.1

2.2

2.4

T_m) 139.2 (°C)

∆H_u) 19.5 (cal/g)

T_m) 142.5 (°C)

∆H_u) 24.4 (cal/g)

[T_m] ) 127 (°C)

[mmmm] ) 84%

T_m) 145.0 (°C)

[mmmm] ) 98%

8

9

CGCTiMe₂

E

P

110

60

30

2

5.0

1.5

120

0.20

0.93

0.65

8.00 × 10⁴2.05 × 10⁶

1.90 × 10⁷4.11 × 10⁴

1.63 × 10⁴6.97 × 10⁴

c

Me₂Si(Ind)₂ZrMe₂

10

60

20

^aCarried out at 1.0 atm ethylene (E) or propylene (P) pressure in 50 mL of toluene on a high-vacuum line. ^bIn units of grams of polymer/(mole

of cat.‚atm‚h). ^cActivated with Ph₃C⁺B(C₆F₅)₄for this comparative run.

-

Table 14. Mole Fractions ([H]), Monomer Sequence Distributions, Reactivity Ratios (r), and Average Sequence Lengths (n) for

Ethylene-1-Hexene Copolymers Obtained from Metallocene/Borane Catalysts

HE

EH

HHE

EEH

catalyst

[H]

HH

EE

EHE EHH HHH HEH HEE EEE

r_E

r_H

n_E

n_H

Cp′TiMe₃, B(C₆F₅)₃(25 °C)^a0.395 0.096 0.598 0.307 0.240 0.118 0.037 0.161 0.276 0.169

5.134 0.064 2.030 1.326

6.228 0.147 2.247 1.737

0.145 3.409 1.725

3.073 0.408 1.616 3.040

3.379 0.418 1.677 3.088

Cp′TiMe₃, PBB (25 °C)^a

CGCZrMe₂, PBB (25 °C)^a

CGCTiMe₂, PBB (25 °C)^a

CGCTiMe₂, PBB (60 °C)^a

0.436 0.185 0.503 0.313 0.155 0.191 0.088 0.103 0.295 0.165

0.336 0.141 0.390 0.469 0.081 0.227 0.027 0.030 0.330 0.304 12.03

0.653 0.438 0.429 0.132 0.078 0.273 0.302 0.132 0.166 0.049

0.648 0.438 0.419 0.142 0.071 0.277 0.299 0.074 0.272 0.006

^aTemperature of polymerization.

structure of 21 (vide supra), the strongly ion-paired anion PBA^-

coordinatively “intrudes” into the cation coordination sphere,

which may account for the decrease of polymerization activity

and the enhancement in stereoselectivity. In addition to

introducing steric perturbations in the monomer activation/

insertion zone, such strong cation-anion interactions may

prevent (or minimize) growing polymer chain isomerization

(epimerization of the last-inserted polymer unit)³⁹and thereby

increase stereoselectivity. The significantly more rapid rate of

anion racemization (k(60 °C) ) 86.7 s^-1) over the polymeri-

zation propagation rate (k(60 °C) ∼ 0.2 s^-1) for catalyst 21 under

the present conditions argues that the chirality of the coordinated

chiral C₃-symmetric PBA^-anion does not directly contribute

(in a chirality transfer sense) to the observed enhancement in

stereoselection.

G. Microstructures of Poly(ethylene-1-hexenes) Obtained

from the Metallocene/Borane Catalyst Systems. Table 14

summarizes microstructure data for representive poly(ethylene-

co-1-hexene) samples obtained from Cp′TiMe₃- and CGCMMe₂-

mediated polymerizations activated with B(C₆F₅)₃and PBB in

terms of compositions, monomer sequence distributions, reactiv-

ity ratios, and average sequence lengths. Figure 10 shows the

¹³C NMR spectrum of a typical ethylene-1-hexene copolymer

produced from Cp′TiMe₃/PBB and peak assignments based on

the literature.²²In the table, the mole fractions of each monomer

are given by the respective sums of the three like-centered triads:

(39) (a) Busico, V.; Caporaso, L.; Cipullo, R.; Landriani, L.; Angelini,

G.; Margonelli, A.; Segre, A. C. J. Am. Chem. Soc. 1996, 118, 2105-

2106. (b) Leclerc, M. K.; Brintzinger, H.-H. J. Am. Chem. Soc. 1996, 118,

9024-9032. (c) Busico, V.; Cipullo, R. J. Am. Chem. Soc. 1994, 116, 9329-

9330.

Figure 9. ¹³C NMR spectra of the polypropylene methyl pentad region

for polymer obtained using (A) rac-Me₂Si(Ind)₂ZrMe₂/Ph₃C⁺B(C₆F₅)₄

-

or (B) rac-Me₂Si(Ind)₂ZrMe₂/Ph₃C⁺PBA^-as the polymerization cata-

lyst.

Metallocene Polymerization Processes

J. Am. Chem. Soc., Vol. 120, No. 25, 1998 6305

Perhaps the most interesting aspect of the copolymer micro-

structures obtained with mono-CpTi catalysts is that PBB

activation promotes higher 1-hexene incoporation (Cp′TiMe₃/

PBB, 43.6% versus Cp′TiMe₃/B(C₆F₅)₃, 39.5%), and substan-

tially improves the randomness of comonomer incorporation

with the product of monomer reactivity ratios (r_E‚r_H) approach-

ing unity for random 1-hexene incoporation for the Cp′TiMe₃/

PBB catalyst and the product of r_E‚r_H) 0.33, suggesting

somewhat alternating character for the Cp′TiMe₃/B(C₆F₅)₃

catalyst. For copolymers produced by the CGC catalysts, the

Ti catalysts incorporate 1-hexene in larger quantities (up to 65%)

than the Zr catalyst (34%); however, the copolymer obtained

with the Zr catalyst is more blocky than that obtained with the

Ti catalyst (CGCTiMe₂/PBB), and the temperature of polym-

erization shows no noticeable influence on the copolymer

microstructure.

Summary

Figure 10. ¹³C NMR spectrum of poly(ethylene-co-1-hexene) obtained

with Cp′TiMe₃/PBB.

We have synthesized two sterically encumbered perfluoroaryl

borane and aluminate cocatalysts; isolated a broad series of

generally stable, highly active Ti, Zr, Hf, and Th ion-paired

cationic complexes derived therefrom; and studied solution

dynamic behavior and solid-state structures as well as polym-

erization catalysis using these complexes. The solution chem-

istry, solid-state structures, and polymerization behavior of these

complexes are internally self-consistent and afford considerable

insight into the nature of these species as well as how

polymerization activity and stereoregulation are substantially

influenced by the nature of cation-anion ion pairing structures.

These results illustrate the substantial and surprising differ-

ences in cation-anion ion pair structure and reactivity that can

be brought about by anions differing in main group metal centers

and perfluoroaryl substituent architecture. For anions that

coordinatively “avoid” (in the case of MePBB^-) or “intrude”

into (in the case of PBA^-) the cation coordination sphere having

a specific intrinsic steric and electronic character, the effects

on polymerization characteristics can be dramatic.

The monomer reactivity ratios r_E(for ethylene) and r_H(for

1-hexene) were estimated from ¹³C NMR spectra using the

following equations:⁴⁰

where [EE], [EH], and [HH] represent diad sequence distribu-

tions in the copolymers and X is the concentration ratio of

ethylene to 1-hexene in the feed. This assay yields similar

results to those obtained by the Fineman-Ross method,⁴¹and

a satisfactory correlation has been demonstrated between the

two techniques.⁴²Finally, presented in the table are the average

sequence lengths for each type of unit all simply calculated from

the following equations:^22b

Acknowledgment. This research was supported by the U.S.

Department of Energy (DE-FG 02-86 ER 13511). Y.X.C. thanks

Akzo-Nobel Chemicals for a postdoctoral fellowship. We thank

Dr. Shengtian Yang for assistance with the 2-D NMR measure-

ments.

where N is given by

Supporting Information Available: Diagram of the po-

lymerization reaction flask. Complete X-ray experimental

details and tables of bond lengths, angles, and positional

parameters for the crystal structures of 3, 13, 14, 19, and 21

(159 pages, print/PDF). See any current masthead page for

ordering information and Web access instructions.

(40) Soga, K.; Uozumi, T. Makromol. Chem. 1992, 193, 823.

(41) Herfert, N.; Montag, P.; Fink, G. Makromol. Chem. 1993, 194, 3167.

(42) Quijada, R.; Dupont, J.; Miranda, M. S. L.; Scipioni, R. B.; Galland,

G. B. Macromol. Chem. Phys. 1995, 196, 3991.

JA973769T

Article Doi

Sterically encumbered (perfluoroaryl) borane and aluminate cocatalysts for tuning cation - Anion ion pair structure and reactivity in metallocene polymerization processes. A synthetic, structural, and polymerization study

DOI: 10.1021/ja973769t

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Article abstract of DOI:10.1021/ja973769t

Full text of DOI:10.1021/ja973769t

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