Ionic Liquid-Promoted Formylation of N(sp<sup>2</sup>)-Heteroarenes with CO<sub>2</sub>/H<sub>2</sub> over Pd/C
Ruipeng Li, Yanfei Zhao, Huan Wang, Dongyang Li, Yunyan Wu, Hongye Zhang, Minhao Tang, Zhimin Liu
Abstract
A solvent plays an important role in chemical synthesis. Herein, we report ionic liquid (IL)-promoted formylation of N(sp2)-heteroarenes with CO2 and H2 to produce formamides over the Pd/C nanocatalyst. It was found that the combination of Pd/C with CO2-reactive IL, for example, tetrabutylphosphonium succinimide ([P4444][Suc]), achieved the hydrogenation of N(sp2)-heteroarenes and subsequent formylation with CO2/H2. A mechanism investigation indicated that [P4444][Suc] could simultaneously activate CO2 and N-heteroarenes via forming carbamate and hydrogen bonds, respectively; meanwhile, it could modify the catalytic activity of metal Pd via electron transfer, thus accomplishing the production of formamides from N(sp2)-heteroarenes and CO2/H2 in combination with Pd/C. This catalytic system was tolerant to a wide substrate scope, affording the corresponding formamides in moderate to high yields. The high efficacy enables the designed IL-Pd/C catalytic system of high practical potential.