Cobalt-Bis(imino)pyridine-Catalyzed Asymmetric Hydrogenation: Electronic Structure, Mechanism, and Stereoselectivity

Academic and industrial efforts aim at replacing precious metal catalysts with cheaper and more environmentally friendly base metal variants. Two cobalt-bis(imino)pyridine (CoBIP) complexes were recently reported as promising candidates for asymmetric hydrogenation [Monfette, S.; et al. J. Ant Chem. Soc. 2012, 134, 4561-4564]. A comprehensive quantum mechanical analysis of these complexes is reported here, including electronic structures, preferred conformations, and mechanisms of activation. The full asymmetric hydrogenation mechanism is analyzed, and the origin of the observed enantioselectivities with both CoBIP catalysts is evaluated. A key finding is that CoBIP complexes catalyze a competing alkene isomerization reaction, which can have crucial implications for the yield and the stereochemical outcome of alkene hydrogenation.