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= $$ 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.