A R T I C L E S
Li et al.
Scheme 1. Mechanism for Long Chain Branch Formation in
Ethylene Homopolymerization Mediated by Constrained Geometry
Catalysts
polymerization experiments or in large-scale production facili-
ties, catalyst concentrations are typically very low (10-4-10-8
M). This raises the intriguing question of whether appropriately
designed bimetallic structures having two sterically open active
centers in close proximity might provide high local catalyst
concentrations and hence exhibit enhanced selectivity for
distinctive enchainment pathways, including those which nor-
mally require sequential intermolecular process at two different
metal centers. Possible consequences could include the pos-
sibility of synthesizing polymeric products having significantly
altered microstructures.
Group 4 “constrained geometry catalysts” (CGC) are well-
known single-site polymerization catalysts8 that produce branched
polyethylenes under conditions in which vinyl-terminated, chain-
transferred macromolecules enjoy a significant probability of
competitive reinsertion into the growing polymer chain at a
second (remote) catalyst center (Scheme 1). The resulting small
but significant levels of long-chain branching lead to highly
desirable materials properties.8 The intriguing question then
arises whether if two CGC catalyst centers could be held in
Scheme 2. Catalyst-Cocatalyst Nuclearity Matrix
(4) Systems with direct metal-metal bonds: (a) Fukuoka, A.; Fukagawa, S.;
Hirano, M.; Koga, N.; Komiya, S. Organometallics 2001, 20, 2065-2075.
(b) Fulton, J. R.; Hanna, T. A.; Bergman, R. G. Organometallics 2000,
19, 602-614. (c) Fabre, S.; Findeis, G.; Trosch, J. M.; Gade, L. H.; Scowen,
I. J.; McPartlin, M. Chem. Commun. 1999, 577-578. (d) Schubart, M.;
Mitchell, G.; Gade, L. H.; Kottke, T.; Scowen, I. J.; McPartlin, M. Chem.
Commun. 1999, 233-234. (e) Catalysis by Di- and Polynuclear Metal
Cluster Complexes; Adams, R. D., Cotton, F. A., Eds.; Wiley-VCH: New
York, 1998; see also references therein. (f) Schneider, A.; Gade, L. H.;
Breuning, M.; Bringmann, G.; Scowen, I. J.; McPartlin, M. Organometallics
1998, 17, 1643-1645. (g) Misumi, Y.; Ishii, Y.; Hidai, M. J. Chem. Soc.,
Dalton Trans. 1995, 3489-3496 (h) Adams, R. D.; Barnard, T. S.; Lu, Z.;
Wu, W.; Yamamoto, J. H. J. Am. Chem. Soc. 1994, 116, 9103-9113.
(5) For recent reviews of single-site olefin polymerization, see (a) Pedeutour,
J.-N.; Radhakrishnan, K.; Cramail, H.; Deffieux, A. Macromol. Rapid
Commun. 2001, 22, 1095-1123. (b) Gladysz, J. A., Ed.; Chem. ReV. 2000,
100 (special issue on “Frontiers in Metal-Catalyzed Polymerization”). (c)
Marks, T. J.; Stevens, J. C., Eds.; Topics Catal. 1999, 15, and references
therein. (d) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem.,
Int. Ed. 1999, 38, 428-447. (e) Kaminsky, W.; Arndt, M. AdV. Polym.
Sci. 1997, 127, 144-187. (f) Bochmann, M. J. Chem. Soc., Dalton Trans.
1996, 255-270. (g) Brintzinger, H.-H.; Fischer, D.; Mu¨lhaupt, R.; Rieger,
B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143-1170.
(h) Catalyst Design for Tailor-Made Polyolefins; Soga, K., Terano, M.,
Eds.; Elsevier: Tokyo, 1994. (i) Mo¨hring, P. C.; Coville, N. J. J.
Organomet. Chem. 1994, 479, 1-29. (j) Marks, T. J. Acc. Chem. Res. 1992,
25, 57-65.
sufficiently close spacial proximity and in proper mutual
orientations, an eliminated, olefin-terminated fragment might
have an enhanced probability of being captured/enchained by
a proximate active center before diffusing away. The possibility
of cooperative effects between the two metal centers might
likewise have a significant influence on the course of olefinic
copolymerizations. Such nuclearity effects would be of both
fundamental scientific and technological interest if new, more
efficient ways to enhance comonomer incorporation and chain
branching could be discovered.
(6) For polymerization studies with binuclear metallocenes, see ref 7 and (a)
Spaleck, W.; Ku¨ber, F.; Bachmann, B.; Fritze, C.; Winter, A. J. Mol. Catal.
A: Chem. 1998, 128, 279-287. (b) Yan, X.; Chernega, A.; Green, M. L.
H.; Sanders, J.; Souter, J.; Ushioda, T. J. Mol. Catal. A: Chem. 1998,
128, 119-141. (c) Soga, K.; Ban, H. T.; Uozumi, T. J. Mol. Catal. A:
Chem. 1998, 128, 273-278. (d) Bochmann, M.; Cuenca, T.; Hardy, D. T.
J. Organomet. Chem. 1994, 484, C10-C12. (e) Jungling, S.; Mu¨lhaupt,
R.; Plenio, H. J. Organomet. Chem. 1993, 460, 191-195.
(7) (a) Lee, D. H.; Yoon, K. B.; Lee, E. H.; Noh, S. K.; Byun, G. G.; Lee, C.
S. Macromol. Rapid Commun. 1995, 16, 265-268. (b) Lee, D. H.; Yoon,
K. B.; Noh, S. K.; Kim, S. C.; Huh, W. S. Macromol. Rapid Commun.
1995, 16, 265-268. (c) Noh, S. K.; Byun, G. G.; Lee, C. S.; Lee, D. H.;
Yoon, K. B.; Kang, K. S. J. Organomet. Chem. 1996, 518, 1-6. (d) Noh,
S. K.; Kim, J. M.; Jung, J. H.; Ra, C. S.; Lee, D. H.; Lee, H. B.; Lee, S.
W.; Huh, W. S. J. Organomet. Chem. 1999, 580, 90-97. (e) Noh, S. K.;
Kim, S. C.; Kim, J. H.; Lee, D. H.; Yoon, K. B.; Lee, H. B.; Lee, S. W.;
Huh, W. S. J. Polym. Sci., Part A: Polym. Chem. 1997, 35, 3717-3728.
(8) (a) Chum, P. S.; Kruper, W. J.; Guest, M. J. AdV. Mater. 2000, 12, 1759-
1767. (b) Alt, H. G.; Fo¨ttinger, K.; Milius, W. J. Organomet. Chem. 1999,
572, 21-30. (c) Harrison, D.; Coulter, I. M.; Wang, S. T.; Nistala, S.;
Kuntz, B. A.; Pigeon, M.; Tian, J.; Collins, S. J. Mol. Catal. A: Chem.
1998, 128, 65-77. (d) Nesarikar, A. R.; Carr, S. H.; Khait, K.; Mirabella,
F. M. J. Appl. Polym. Sci. 1997, 63, 1179-1187. (e) Soga, K.; Uozumi,
T.; Nakamura, S.; Toneri, T.; Teranishi, T.; Sano, T.; Arai, T.; Shiono, T.
Macromol. Chem. Phys. 1996, 197, 4237-4251. (f) Devore, D. D.;
Timmers, F. J.; Hasha, D. L.; Rosen, R. K.; Marks, T. J.; Deck, P. A.;
Stern, C. L. Organometallics 1995, 14, 3132-3134. (g) Stevens, J. C. Proc.
MetCon Houston, 1993, 157. (h) Lai, S. Y.; Wilson, J. R.; Knight, G. W.;
Stevens, J. C. WO-93/08221, 1993. (i) 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.) (j) Devore, D. D. Eur. Pat.
Appl. EP-514-828-A1, Nov 25, 1992. (k) Stevens, J. C.; Timmers, F. J.;
Wilson, D. R.; Schmidt, G. F.; Nickias, P. N.; Rosen, R. K.; Knight, G.
W.; Lai, S. Eur. Pat. Appl. EP 416 815-A2, 1991 (Dow Chemical Co.).
Two means (covalent and electrostatic) of bringing single-
site polymerization catalyst centers into close proximity are
illustrated in the nuclearity matrix of Scheme 2. We report9 here
the synthesis, characterization, and comparative ethylene ho-
mopolymerization characteristics of all four members of such
a seriessprepared from the new bimetallic “constrained geom-
etry” catalyst (CGC), M ) zirconium complex (µ-CH2CH2-
3,3′){(η5-indenyl )[1- Me2Si(tBuN)](ZrMe2)}2 [EBICGC(ZrMe2)2]
(Zr2), the monometallic analogue [1-Me2Si(3-ethylindenyl)-
(tBuN)]ZrMe2 (Zr1) for control experiments, as well as the new
binuclear bisborate cocatalyst (Ph3C+)2[1,4-(C6F5)3BC6F4B-
(C6F5)3]2- (B2),10 and Ph3C+B(C6F5)4 (B1). The ethylene +
-
1-hexene and ethylene + 1-pentene copolymerization charac-
(9) For a preliminary communication of certain parts of this work, see (a) Li,
L.; Metz, M. V.; Marks, T. J.; Liable-Sands, L.; Rheingold, A. Polymer
Preprints, 2000, 41, 1912-1913. (b) Patton, J. T.; Marks, T. J.; Li, L.
WO9914222A1, March 25, 1999.
9
12726 J. AM. CHEM. SOC. VOL. 124, NO. 43, 2002