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 gel 60N or CARiACT Q-10) as a support, were synthesized through surface functionalization. The supported phosphines ( 1a, b ) were structurally characterized by solid-state 13 C, 29 Si, and 31 P 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 13 C and 31 P CP/MAS NMR spectroscopies and Rh K-edged X-ray absorption fine structure (XAFS) measurements. Heterogeneous catalysts that were prepared from [RhCl(C 2 H 4 ) 2 ] 2 and 1a, b showed exceptionally high catalytic activities for the reaction of sterically hindered ketones (including di- tert -butyl ketone) and triorganosilanes such as Et 3 SiH and ( t -Bu)Me 2 SiH. The catalyst from 1b showed no leaching of rhodium after reaction and was reusable without decrease of the activity.