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

The prototypical reactivity profiles of transition metal dihydrogen complexes (M-H-2) 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 H(2)activation, namely direct activation through H-atom or hydride transfer from the sigma-H(2)adducts. To this end, we describe herein the reactivity of an isostructural pair of a neutralS=1/2and an anionicS=0 Co-H(2)adduct, both supported by a trisphosphine borane ligand (P-3(B)). The thermally stable metalloradical, (P-3(B))Co(H-2), serves as a competent precursor for hydrogen atom transfer to Bu3ArO. What is more, its anionic derivative, the dihydrogen complex [(P-3(B))Co(H-2)](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-H(2)complexes known.