Rhodium-grafted hydrotalcite catalyst for heterogeneous 1,4-addition reaction of organoboron reagents to electron deficient olefins

Abstract

A rhodium-grafted hydrotalcite (Rh/HT) was prepared by the treatment of a Mg–Al mixed hydroxide (hydrotalcite, HT) with an aqueous RhCl₃·nH₂O solution. The formation of the Rh^III species on the HT surface was confirmed by X-ray absorption fine structure spectroscopy. The Rh/HT catalyst was demonstrated to effectively promote the 1,4-addition reaction of organoboron reagents to electron-deficient olefins in both organic and aqueous solvents. The strong surface basicity of HT facilitates the formation of a Rh–OH species, which possesses high nucleophilicity, leading to an efficient transmetalation with organoboron reagents. This catalyst system is also applicable in the one-pot three-component synthesis of 2-cyano-3,3-diphenyl propionate due to the bifunctionality of the Rh/HT surface.