Mechanistic study on the photo carboxylation of benzylic C-H bonds by xanthone and Ni(0) catalysts

Abstract The photo carboxylation of the benzylic C(sp3)-H bond catalyzed by xanthone/nickel were examined by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. This study corroborates the previous proposal that light promotes the H-transfer from benzylic C(sp3)-H bond of the p-methoxytoluene to excited state of photocatalyst xanthone. Meanwhile, Ni(0) catalyst could mediate the H-transfer to occur via an electron-coupled-proton transfer manner, and then remarkably facilitates the carboxylation step (compared to the Ni-absent systems). After that, the generated Ni(I) intermediate and ketyl radical anion complete the carboxylation and electron transfer processes independently.