Synthesis of Silica-Supported Compact Phosphines and Their Application to Rhodium-Catalyzed Hydrosilylation of Hindered Ketones with Triorganosilanes

Solid-supported phosphine ligands silica-SMAPs {[silica gel 60N]-SMAP (1a) or [CARiACT Q-10]-SMAP (1b)}, which are composed of a caged, compact trialkylphosphine (SMAP) as a ligand and silica gel (silica get 60N or CARiACT Q-10) as a support,'were synthesized through surface functionalization. The supported phosphines (1a,b) were structurally characterized by solid-state C-13, Si-29, and P-31 cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopies and N-2 adsorption measurements. Complexation of 1a,b with [RhCl(cod)](2) afforded a mono(phosphine)-rhodium complex Silica-SMAP-RhCl(cod) exclusively, even in the presence of excess ligands, as proved by solid-state C-13 and P-31 CP/MAS NMR spectroscopies and Rh K-edged X-ray'absorption fine structure (XAFS) measurements. Heterogeneous catalysts that were prepared from [RhCl(C2H4)(2)](2) and 1a,b showed exceptionally high catalytic activities for the reaction of sterically hindered ketones (including di-tertbutyl ketone) and triorganosi lanes such as Et3SiH and (t-Bu)Me2SiH. The catalyst from 1b showed no leaching of rhodium after reaction and was reusable without decrease of the activity.