Carboxylation of Aromatics by CO₂ under “Si/Al Based Frustrated Lewis Pairs” Catalytic System

Abstract

Carboxylation of aromatics by CO 2 to generate corresponding carboxylic acids is recently providing a novel approach to utilize the green gas CO 2 , in which the activation of CO 2 is the key procedure. Among the many catalytic systems employed in the carboxylation, the concept of “Frustrated Lewis Pairs” (FLPs) was scarcely mentioned, which perform excellently in activating small molecules like CO 2 . The FLPs are combinations of Lewis acids and Lewis bases which failed to form adducts due to their bulky steric congestion. In this paper, we first attempted various Si/Al Based FLPs to catalyze the carboxylation of aromatics through the activation of CO 2 , and a good yield of 62% - 97% was obtained. The reaction mechanism was proposed, involving the activation of CO2 mainly contributed by AlCl 3 in cooperation with organosilane, forming an intermediate consisting of CO 2 , AlCl 3 , and R 4 Si, as well as the subsequent electrophilic attack to aromatics, thus to promote the carboxylation reaction.