Transfer Semihydrogenation of Alkynes Catalyzed by Imidazo[1,5-a]pyrid-3-ylidene-Pd Complexes: Positive Effects of Electronic and Steric Features on N-Heterocyclic Carbene Ligands

To investigate the catalytic utility of the imidazo[1,5-a]pyrid-3-ylidene (IPC) ligand, Pd-catalyzed transfer semihydrogenation of alkynes with formic acid as a hydrogen source was conducted. The steric bulkiness of the substituent on N2 affected the configuration of the pi-allyl moiety of the precatalyst of IPC-Pd-pi-allyl complexes and the robustness of the catalytic process. The catalytic activities of IPC-Pd complexes were clearly higher than those of conventional NHC-Pd complexes.