Effective Pincer Cobalt Precatalysts for Lewis Acid Assisted CO2 Hydrogenation

The pincer ligand MeN[CH2CH2((PPr2)-Pr-i)](2) (iPIPNP) was employed to support a series of cobalt(I) complexes, which were crystallographically characterized. A cobalt monochloride species, ((PNP)-P-iPr)CoCl, served as a precursor for the preparation of several cobalt precatalysts for CO2 hydrogenation, including a cationic dicarbonyl cobalt complex, [((PNP)-P-iPr)Co(CO)(2)](+). When paired with the Lewis acid lithium triflate, [(PNP)-P-iPr)Co(CO)(2)] affords turnover numbers near 30 000 (at 1000 psi, 45 degrees 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 [CPTNP)Co] complex.