Synthesis of Molybdenum Complexes Bearing Pyridine-Based PNP-Type Pincer Ligands with Pendent Pyridyl Unit and Their Catalytic Activity for Ammonia Formation

Molybdenum trichloride complexes bearing pyridine-based PNP-type pincer ligands with a pendent pyridyl unit as a proton mediating moiety are newly designed and synthesized for the aim to promote proton-coupled electron transfer in catalytic ammonia formation from dinitrogen. X-ray analysis of the molybdenum trichloride complexes reveals that the pendent pyridyl unit introduced at the benzylic position of the pyridine skeleton in the pincer ligand is located at an appropriate place for donating protons. Unfortunately, the newly prepared molybdenum complexes do not work as effective catalysts for ammonia formation. It is considered that the pendent pyridyl unit is unexpectedly coordinated to the molybdenum center to suppress the activation of the dinitrogen molecule.