Direct Covalent Immobilizaion of Chiral Phosphine Oxide: Hollow Mesoporous Polystyrene Nanospheres As a Platform for Efficient Heterogeneous Enantioselective Reductive Aldol Reaction

The heterogeneous catalysis of expensive chiral phosphine oxides suffers from multi-step tedious immobilization and limited mass transfer due to its bulky volume. In this paper, a simple and direct strategy for covalently anchoring (S)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl dioxide (BINAPO) to hollow mesoporous polystyrene nanospheres (HMPNs) is developed to fabricate HMPNs-supported BINAPO (HMPNs@BINAPO) via one-pot Friedel-Crafts alkylation. HMPNs@BINAPO possesses a nanoscale and spherical morphology with a thin and mesoporous shell suitable for fast mass transfer of reactants and products. In the asymmetric reductive aldol reaction of alpha, beta-unsaturated ketones and benzaldehydes with HSiCl3, HMPNs@BINAPO shows the comparable good to excellent catalytic performances to homogeneous BINAPO and good reusability without an obvious decrease in diastereoselectivity and enantioselectivity.