Cationic Alkylaluminum-Complexed Zirconocene Hydrides: NMR-Spectroscopic Identification, Crystallographic Structure Determination, and Interconversion with Other Zirconocene Cations

• Published in: Journal of the American Chemical Society 2011-02, Vol.133 (6), p.1805-1813
• Main Authors: Baldwin, Steven M., Bercaw, John E., Henling, Lawrence M., Day, Michael W., Brintzinger, Hans H.
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja1050428

The ansa-zirconocene complex rac-Me2Si(1-indenyl)2ZrCl2 ((SBI)ZrCl2) reacts with diisobutylaluminum hydride and trityl tetrakis(perfluorophenyl)borate in hydrocarbon solutions to give the cation [(SBI)Zr(μ-H)3(Al i Bu2)2]+, the identity of which is derived from NMR data and supported by a crystallographic structure determination. Analogous reactions proceed with many other zirconocene dichloride complexes. [(SBI)Zr(μ-H)3(Al i Bu2)2]+ reacts reversibly with ClAl i Bu2 to give the dichloro-bridged cation [(SBI)Zr(μ-Cl)2Al i Bu2]+. Reaction with AlMe3 first leads to mixed-alkyl species [(SBI)Zr(μ-H)3(AlMe x i Bu2−x )2]+ by exchange of alkyl groups between aluminum centers. At higher AlMe3/Zr ratios, [(SBI)Zr(μ-Me)2AlMe2]+, a constituent of methylalumoxane-activated catalyst systems, is formed in an equilibrium, in which the hydride cation [(SBI)Zr(μ-H)3(AlR2)2]+ strongly predominates at comparable HAl i Bu2 and AlMe3 concentrations, thus implicating the presence of this hydride cation in olefin polymerization catalyst systems.