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Updated: Jun 5, 2026

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
Published on: March 20, 2017
Cationic alkylaluminum-complexed zirconocene hydrides: NMR-spectroscopic identification, crystallographic structure
Steven M Baldwin1, John E Bercaw, Lawrence M Henling
1Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, California 91125, United States.
Abstract:
The ansa-zirconocene complex rac-Me(2)Si(1-indenyl)(2)ZrCl(2) ((SBI)ZrCl(2)) reacts with diisobutylaluminum hydride and trityl tetrakis(perfluorophenyl)borate in hydrocarbon solutions to give the cation [(SBI)Zr(μ-H)(3)(Al(i)Bu(2))(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)Bu(2))(2)](+) reacts reversibly with ClAl(i)Bu(2) to give the dichloro-bridged cation [(SBI)Zr(μ-Cl)(2)Al(i)Bu(2)](+). Reaction with AlMe(3) first leads to mixed-alkyl species [(SBI)Zr(μ-H)(3)(AlMe(x)(i)Bu(2-x))(2)](+) by exchange of alkyl groups between aluminum centers. At higher AlMe(3)/Zr ratios, [(SBI)Zr(μ-Me)(2)AlMe(2)](+), a constituent of methylalumoxane-activated catalyst systems, is formed in an equilibrium, in which the hydride cation [(SBI)Zr(μ-H)(3)(AlR(2))(2)](+) strongly predominates at comparable HAl(i)Bu(2) and AlMe(3) concentrations, thus implicating the presence of this hydride cation in olefin polymerization catalyst systems.
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