Exploring the Alcohol Stability of Bis(phosphine) Cobalt Dialkyl Precatalysts in Asymmetric Alkene Hydrogenation

Cobalt complexes bearing enantiopure, bidentate bis­(phosphine) ligands exhibit extraordinary activity and stereoselectivity for the hydrogenation of enamides. Optimal performance was observed in polar protic solvents such as methanol, an industrially preferred green solvent but a medium that is often a poison for reduced Earth abundant metals. The interaction of the low-spin cobalt­(II) dialkyl complex, (R,R)-(iPr-DuPhos)­Co­(CH2SiMe3)2, with alcohols including 4-methoxyphenol, pinacol, and CH3OH was studied. With the alcohols lacking β-hydrogens, cobalt bis­(alkoxide) complexes were isolated and structurally characterized. With methanol, protonolysis of the alkyl ligands was again observed followed by dehydrogenation of the alcohol and [(R,R)-(iPr-DuPhos)­Co]2(μ-CO)2 was isolated. Both solid-state and solution EXAFS studies were conducted to establish the spectroscopic signatures of bis­(phosphine) cobalt­(II) and cobalt(0) complexes relevant to catalytic hydrogenation and also to probe the role of phosphine dissociation in methanol