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 β-position of terminal alkenes. The mechanism of such hydroboration was established by various stoichiometric reactions based on the cobalt(II) hydride. With cooperative CoII–N reactivity for the B–H bond cleavage, our catalysis depends on the CoII–H hydride generated by the system itself.