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Alkylaluminum-complexed zirconocene hydrides: identification of hydride-bridged species by NMR spectroscopy

Baldwin, Steven M. and Bercaw, John E. and Brintzinger, Hans H. (2008) Alkylaluminum-complexed zirconocene hydrides: identification of hydride-bridged species by NMR spectroscopy. Journal of the American Chemical Society, 130 (51). pp. 17423-17433. ISSN 0002-7863. doi:10.1021/ja8054723.

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Reactions of unbridged zirconocene dichlorides, (R_nC_5H_5−n)_2ZrCl_2 (n = 0, 1, or 2), with diisobutylaluminum hydride (HAl^iBu_2) result in the formation of tetranuclear trihydride clusters of the type (R_nC_5H_5−n)_2Zr(μ-H)_3(Al^iBu_2)_3(μ-Cl)_2, which contain three [Al^iBu_2] units. Ring-bridged ansa-zirconocene dichlorides, Me_2E(R_nC_5H_4−n)_2ZrCl_2 with E = C or Si, on the other hand, are found to form binuclear dihydride complexes of the type Me_2E(R_nC_5H_4−n)_2Zr(Cl)(μ-H)_2Al^iBu_2 with only one [Al^iBu_2] unit. The dichotomy between unbridged and bridged zirconocene derivatives with regard to tetranuclear versus binuclear product formation is proposed to be connected to different degrees of rotational freedom of their C_5-ring ligands. Alkylaluminum-complexed zirconocene dihydrides, previously observed in zirconocene-based precatalyst systems activated by methylalumoxane (MAO) upon addition of HAl^iBu_2 or Al^iBu_3, are proposed to be species of the type Me_2Si(ind)_2Zr(Me)(μ-H)_2Al^iBu_2, stabilized by interaction of their terminal Me group with a Lewis acidic site of MAO.

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Additional Information:© 2008 American Chemical Society. Publication Date (Web): November 25, 2008. This research was supported by USDOE Office of Basic Energy Sciences (Grant No. DE-FG03-85ER13431), by Fonds der Chemischen Industrie, and by BASELL Polyolefine GmbH. We are grateful to Professor Peter Burger (University of Hamburg) for DFT calculations on problems related to the work reported here, to Dr. Heike Gregorius (BASELL, Frankfurt/Main) for a gift of a sample of complex 16, and to Dr. Markus Ringwald (MCAT, Konstanz) for gifts of samples of several zirconocene complexes.
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Department of EnergyDE-FG03-85ER13431
Fonds der Chemischen IndustrieUNSPECIFIED
Issue or Number:51
Record Number:CaltechAUTHORS:20090720-141909224
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14619
Deposited By: Ruth Sustaita
Deposited On:08 Aug 2009 20:03
Last Modified:08 Nov 2021 23:13

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