Journal of the American Chemical Society
ARTICLE
Forschungsgemeinschaft (Grants Bri510/14-1 and Me1388/9-1),
by Fonds der Chemischen Industrie, and by BASELL Polyolefine
GmbH. The X-ray diffractometer was purchased via an NSF
CRIF:MU award to the California Institute of Technology,
CHE-0639094.
(11) (a) Eisch, J. J.; Rhee, S. G. J. Organomet. Chem. 1972, 38, C25.
(b) Eisch, J. J.; Rhee, S. G. J. Organomet. Chem. 1972, 42, C73.
(12) Neutral zirconocene hydride complexes with a ZrH3 core
geometry: (a) Khan, K.; Raston, C. L.; McGrady, J. E.; Skelton,
B. W.; White, A. H. Organometallics 1997, 16, 3252. (b) Etkin, N.; Hoskin,
A. J.; Stephan, D. W. J. Am. Chem. Soc. 1997, 119, 11420. (c) Etkin, N.;
Stephan, D. W. Organometallics 1998, 17, 763. (d) Wehmschulte, R. J.;
Power, P. P. Polyhedron 1999, 18, 1885. (e) Sizov, A. I.; Zvukova, T. M.;
Belsky, V. K.; Bulychev, B. M. J. Organomet. Chem. 2001, 619, 36.
(13) Edelmann, F. In Comprehensive Organometallic Chemistry II;
Lappert, M. F., Ed.; Elsevier Scientific Ltd.: Oxford, UK, 1995; Vol. 4, p 11.
(14) For complexes containing an interannular ethanediyl bridge, no
uniform ordering of their doublet and triplet signals is apparent.
(15) The same species, [(SBI)Zr(μ-Cl)2AliBu2]þ, was formed when
(SBI)ZrCl2 was allowed to react with Et3SiH, [Ph3C][B(C6F5)4], and
ClAliBu2 in ratios of 1:150:1:1. Reaction of (SBI)ZrCl2 with Et3SiH and
[Ph3C][B(C6F5)4], without any added chloroaluminum reagent, gave
an insoluble green solid, presumably the [B(C6F5)4]- salt of the dimeric
dication [{(SBI)Zr}2(μ-Cl)2]2þ, which has previously been structurally
characterized: Bryliakov, K. P.; Talsi, E. P.; Semikolenova, N. V.;
Zakharov, V. A.; Brand, J.; Alonso-Moreno, C.; Bochmann, M.
J. Organomet. Chem. 2007, 692, 859. Reaction of this solid with 5 equiv
of ClAliBu2 in benzene-d6 gave a dark blue solution, which displayed the
1H NMR signals of [(SBI)Zr(μ-Cl)2AliBu2]þ (Supporting In-
formation), thus providing further support for the identity of this
species. A reaction of (SBI)ZrMe2 with [Ph3C][B(C6F5)4], AlMe3,
and AlCl3 in ratios of 1:1:6:1 gave the related cation [(SBI)Zr(μ-
Cl)2AlMe2]þ, the ligand C5H signals of which appear at 6.35 and 5.29
ppm, that is, at somewhat lower fields than those of [(SBI)Zr(μ-
Cl)2AliBu2]þ (6.26 and 5.18 ppm).
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(16) Exchange between terminal Me groups of the cation [(SBI)-
i
Zr(μ-Me)2AlMe2]þ and terminal isobutyl groups of Al2(μ-Me)2 Bu4
has been shown to occur to an extent close to statistical expectation:
Babushkin, D. E.; Brintzinger, H. H. Chem.-Eur. J. 2007, 13, 5294.
(17) Reaction of the dimethyl complex (SBI)ZrMe2 with 1 equiv of
[Ph3C][B(C6F5)4], so as to yield the ion pair [(SBI)ZrMeþ
3 3 3
(F5C6)4B-], and subsequently with 4 equiv of HAliBu2, gives rise to
the same pair of doublets at -2.05 ppm, undoubtedly due to the pres-
ence of one {MeAl} unit per zirconocene in this reaction system.
(18) If AlMe3 is added to a reaction system containing trioctyl
aluminum, Zr-H signals due to {Al(octyl)2}- and {AlMe2}-complexed
hydride cations appear with comparable intensities.
(19) In the presence of the large (40-110-fold) excess of added
AlMe3, both cations can be considered to contain mostly Me groups in
their terminal Al-alkyl positions.
(20) This assignment is supported by the observation of a gCOSY
cross-peak in MAO-activated (SBI)ZrCl2 solution containing HAliBu2,
connecting the broad ZrH2 signal at -2.01 ppm to another ZrH
resonance at 0.60 ppm, largely hidden under the low-field tail of the
MAO signal.
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(22) Integration of the Al-H, Al-CH3, and (CH3)2Si signals allows
one to determine the equilibrium concentrations of the four species
involved in this reaction. In accord with Scheme 8, the dimensionless
equilibrium constant Keq is calculated using the expression:
½ðSBIÞZrðμ -MeÞ AlMe2ꢀþ ½ðHAlMe2Þ ꢀ
2
3
½ðSBIÞZrðμ -HÞ ðAlMe2Þ ꢀþ ½ðAlMe3Þ3ꢀ
Keq
¼
3
2
3
2
(See the Supporting Information.) Quantification of this equilibrium
requires that HAlMe2 and AlMe3 are treated, according to their actual
nuclearities, as trimers and dimers, respectively (cf., ref 3). Therefore,
this notation is used here, in deviation from the rest of this Article.
(23) Marvich, R. H.; Brintzinger, H. H. J. Am. Chem. Soc. 1971, 93,
2046.
(10) Baldwin, S. M.; Bercaw, J. E.; Brintzinger, H. H. J. Am. Chem.
Soc. 2010, 132, 13969.
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dx.doi.org/10.1021/ja1050428 |J. Am. Chem. Soc. 2011, 133, 1805–1813