Siloxyaluminum Alkyl Cations: Syntheses, Structures, and Reactions Related to Activation of Zirconocene Catalysts on Silica Gel Surfaces

Binuclear siloxyaluminum methyl complexes of the type Me2Al(μ-OSiR3)2AlMe2 react with
protonated N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate, with release of CH4,
to form the dimethylaniline (DMA)-stabilized siloxyaluminum methyl cations Me2Al(μ-OSiR3)2AlMe(NMe2(C6H5)+. These cations abstract a Cl- ligand from (C5H5)2ZrCl2, to give
the dinuclear cation {(C5H5)2ZrCl}2(μ-Cl)+, and a CH3- ligand from (C5H5)2Zr(CH3)2, to give
by way of the DMA-stabilized cation (C5H5)2Zr(CH3)NMe2(C6H5)+ the CH-activation product
(C5H5)2ZrCH2NMe(C6H5)+; reaction with Me2Si(ind)2ZrMe2 in toluene solution yields a
moderately active catalyst for ethene polymerization. This reactivity of siloxyaluminum
methyl cations is qualitatively similar to, although substantially lower than, that of a silica
gel surface treated with trimethylaluminum and a cationizing agent.