Asymmetric transfer hydrogenation-Sonogashira coupling one-pot enantioselective tandem reaction catalysed by Pd(0)-Ru(III)/diamine-bifunctionalized periodic mesoporous organosilica

Abstract

Construction of a bifunctional heterogeneous catalyst through the immobilization of palladium nanoparticles within ethylene-bridged chiral ruthenium/diamine-functionalized periodic mesoporous organosilica is developed. Structural analyses and characterizations show its well-defined chiral single-site ruthenium species, and electron microscopy reveals its ordered mesostructure. As a bifunctional catalyst, it enables an efficient asymmetric transfer hydrogenation-Sonogashira coupling one-pot enantioselective tandem reaction, where Ru-catalysed asymmetric transfer hydrogenation followed by Pd-catalysed Sonogashira coupling affords various chiral conjugated alkynols in high yields with up to 97% enantioselectivity. As presented in this study, uniformly distributed palladium nanoparticles, high ethylene-bridged hydrophobicity, and single-site chiral ruthenium catalytic nature make a synergistic contribution to its catalytic performance. Furthermore, the high stability of palladium nanoparticles within its organosilicate network promotes high recyclability, and it could be used for the asymmetric transfer hydrogenation-Sonogashira coupling one-pot enantioselective tandem reaction of 4-iodoacetophenone and ethynylbenzene at least seven times without loss of its catalytic activity.