Effective Pincer Cobalt Precatalysts for Lewis Acid Assisted CO2 Hydrogenation

The pincer ligand MeN­[CH2CH2(PiPr2)]2 (iPrPNP) was employed to support a series of cobalt­(I) complexes, which were crystallographically characterized. A cobalt monochloride species, (iPrPNP)­CoCl, served as a precursor for the preparation of several cobalt precatalysts for CO2 hydrogenation, including a cationic dicarbonyl cobalt complex, [(iPrPNP)­Co­(CO)2]+. When paired with the Lewis acid lithium triflate, [(iPrPNP)­Co­(CO)2]+ affords turnover numbers near 30 000 (at 1000 psi, 45 °C) for CO2-to-formate hydrogenation, which is a notable increase in activity from previously reported homogeneous cobalt catalysts. Though mechanistic information regarding the function of the precatalysts remains limited, multiple experiments suggest the active species is a molecular, homogeneous [(iPrPNP)­Co] complex.