Carboxylation of aromatics by CO2 to
generate corresponding carboxylic acids is recently providing a novel approach
to utilize the green gas CO2, in which the activation of CO2 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 CO2. 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 CO2, and a
good yield of 62% - 97% was obtained. The reaction mechanism was proposed, involving
the activation of CO2 mainly contributed by AlCl3 in cooperation with organosilane, forming an intermediate
consisting of CO2, AlCl3, and R4Si, as well as the subsequent electrophilic
attack to aromatics, thus to promote the carboxylation reaction.
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