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

Abstract

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 13C, 29Si, and 31P cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopies and N2 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 13C and 31P 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-tert-butyl ketone) and triorganosilanes 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.

Rhodium-Catalyzed Hydrosilylation of Ketones: Catalyst Development and Mechanistic Insights

“…The reported data and further experiments provided evidence for a rhodium species only coordinated by one phosphine of [silica]-SMAP (10). 61,62 This trend was also seen in other publications where very bulky monodentate phosphines and isocyanides were used in homogeneous systems and proved to be very efficient ligands in rhodium-catalyzed hydrosilylation of ketones. 63−66 Very recently, research has focused on the application of rhodium-catalyzed hydrosilylation in ionic liquids.…”

Tripod Immobilization of Triphenylphosphane on a Silica‐Gel Surface to Enable Selective Mono‐Ligation to Palladium: Application to Suzuki–Miyaura Cross‐Coupling Reactions with Chloroarenes

“…Nitrogen‐adsorption measurements of Silica‐3p‐TPP ([P]=0.20 mmol g −1 ) showed that the surface modification of the CARiACT Q10 silica gel with the tripod phosphane and the TMS groups resulted in a reasonable reduction of structural parameters, such as surface area (284 versus 271 m 2 g −1 ), pore diameter (17.8 versus 15.6 nm), and pore volume (1.32 versus 1.03 mL g −1 ) 17b. On the basis of the surface area value and the TPP loading, the surface P‐atom density for Silica‐3p‐TPP was calculated to be 0.44 nm −2 .…”

Palladium‐Catalyzed Borylation of Sterically Demanding Aryl Halides with a Silica‐Supported Compact Phosphane Ligand

“…5 On the other hand, we have developed Silica‐SMAP, which is a silica‐supported “compact” phosphane ligand 6. 7 Because of its immobilized nature, this ligand forms 1:1 metal/P complexes exclusively with a range of transition‐metal species, despite its extreme compactness 7a,b. We demonstrated that the surface‐bound 1:1 metal/P complexes afford highly active catalysts for the hydrosilylation and the hydrogenation of ketones (with Rh),7a–c and the directed ortho borylation of functionalized arenes (with Ir) 7d–f.…”