Dihydrogen Adduct (Co-H2 ) Complexes Displaying H-Atom and Hydride Transfer.

The prototypical reactivity profiles of transition metal dihydrogen complexes (M-H2 ) are well-characterized with respect to oxidative addition (to afford dihydrides, M(H)2 ) and as acids, heterolytically delivering H+ to a base and H- to the metal. In the course of this study we explored plausible alternative pathways for H2 activation, namely direct activation through H-atom or hydride transfer from the σ-H2 adducts. To this end, we describe herein the reactivity of an isostructural pair of a neutral S= 1 / 2 and an anionic S=0 Co-H2 adduct, both supported by a trisphosphine borane ligand (P3 B ). The thermally stable metalloradical, (P3 B )Co(H2 ), serves as a competent precursor for hydrogen atom transfer to t Bu3 ArO⋅ . What is more, its anionic derivative, the dihydrogen complex [(P3 B )Co(H2 )]1- , is a competent precursor for hydride transfer to BEt3 , establishing its remarkable hydricity. The latter finding is essentially without precedent among the vast number of M-H2 complexes known.