[(CH₃)₅C₅]₂Th(CH₃)₂/Silica Surface Chemistry. High-Resolution ¹³C CPMAS NMR Evidence for Alkylation of Surface Silicon Sites

The reaction of Cp’₂Th(¹³CH₃)₂ (Cp’ = η⁵-Me₅C₅) with dehydroxylated silica (ca. 0.4 surface OH/nm²) has been studied by high-resolution ¹³C CPMAS NMR spectroscopy. On the basis of ¹³C chemical shifts, relative signal intensities, and NMR data from model compounds and model reactions, it is proposed that the predominant adsorption pathway involves methyl transfer from thorium to surface silicon sites. The products of this Si-O cleavage process are surface Si-CH₃ and Cp’₂Th(CH₃)-siloxide functionalities. The resulting thorium environment appears to be somewhat more electron rich than in the analogous surface complex on dehydroxylated γ-alumina.