Effective Pincer Cobalt Precatalysts for Lewis Acid Assisted CO₂ Hydrogenation

The pincer ligand MeN­[CH₂CH₂(P^<i>i</i>Pr₂)]₂ (^<i>i</i>PrPNP) was employed to support a series of cobalt­(I) complexes, which were crystallographically characterized. A cobalt monochloride species, (^<i>i</i>PrPNP)­CoCl, served as a precursor for the preparation of several cobalt precatalysts for CO₂ hydrogenation, including a cationic dicarbonyl cobalt complex, [(^<i>i</i>PrPNP)­Co­(CO)₂]⁺. When paired with the Lewis acid lithium triflate, [(^<i>i</i>PrPNP)­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 [(^<i>i</i>PrPNP)­Co] complex