Polymer@silica composites with tunable outer and inner surface properties: a platform for aqueous asymmetric transfer hydrogenation

Abstract

A highly efficient chiral solid catalyst was synthesized via in situ polymerization of a chiral monomer (1R,2R)-N¹-(4-vinylbenzenesulfonyl)-1,2-diphenylethane-1,2-diamine (VBS-DPEN) together with divinylbenzene (DVB) in the nanocages of mesoporous silica (FDU-12) followed by coordination with a metal precursor [Cp*RhCl₂]₂ (Cp* = pentamethylcyclopentadiene). The solid chiral catalyst with hydrophilic outer and hydrophobic inner surface properties could be well dispersed in aqueous solution and facilitate the adsorption of hydrophobic ketones in it. As a result, it could efficiently catalyze the aqueous asymmetric transfer hydrogenation (ATH) of ketones to afford 94% ee and a much higher TOF than homogeneous Rh-TsDPEN (TOF 585 versus 340 h⁻¹). Our studies suggest that the dispersion of polymers in the nanopores of mesoporous silica could provide a new approach to the synthesis of high performance solid catalysts for organic reactions in water.