A superhydrophobic mesostructured silica as a chiral organometallic immobilization platform for heterogeneous asymmetric catalysis

Abstract

Immobilization of molecular catalysts in a superhydrophobic material can efficiently overcome the shortage of low catalytic efficiency in heterogeneous catalysis. In this study, by taking advantage of a superhydrophobic mesostructured silica as a support, we incorporated conveniently chiral diamine to the silicate network, thus constructing two hydrophobic rhodium/diamine- and ruthenium/diamine-functionalized heterogeneous catalysts. Analyses via solid-state carbon NMR spectroscopy disclosed the well-defined single-site active species in the silicate framework of these catalysts, while the water contact angle measurements reflected their high hydrophobicity. Characterizations via scanning and transmission electron microscopy revealed their monodispersed feature. As presented in the study, the hydrophobic rhodium/diamine-functionalized catalyst greatly promotes the enantioselective tandem reduction/lactonization of ethyl 2-acylarylcarboxylates to afford various chiral phthalides, whereas the hydrophobic ruthenium/diamine-functionalized catalyst boosts an efficient asymmetric transfer hydrogenation-dynamic kinetic resolution process for construction of 1,2-distereocentered diethyl α-benzoyl-β-hydroxyphosphonates. As envisaged, the as-made catalysts with high hydrophobicity and uniformly distributed single-site catalytically active nature make combinational contributions to their catalytic performances, affording chiral products in high yields with up to 99% enantioselectivity. Moreover, the catalysts can be also recovered easily and recycled repeatedly, making them attracting candidates in efficient organic transformations.