Addition of a B-H Bond across an Amido-Cobalt Bond: CoII-H-Catalyzed Hydroboration of Olefins

This paper describes a well-defined cobalt(II) half-sandwich complex bearing a phosphinoaminato ligand, Cp*Co(1,2-Ph2PC6H4NH) (1), that can activate pinacolborane (HBpin) for catalytic terminal hydroboration of olefins. The cooperative cobalt(II)-amido reactivity in 1 enables the B-H bond cleavage, affording the 17-electron cobalt(II) hydride Cp*Co(1,2-Ph2PC6H4NH (Bpin)), abbreviated H1(Bpin), in which the borenium ion is captured by the uncoordinated nitrogen atom of the phosphinoaminato ligand. Hydroboration of the C=C bond can be promoted by a heteroatom such as N or O at the beta-position of terminal alkenes. The mechanism of such hydroboration was established by various stoichiometric reactions based on the cobalt(II) hydride. With cooperative Co-II-N reactivity for the B-H bond cleavage, our catalysis depends on the Co-II-H hydride generated by the system itself.