Influence of phosphine (pincer) ligands on the transition metal hydrides reactivity

Abstract

• Dihydrogen bonding determines reactivity of metal hydrides. • Role of (di)hydrogen bonding and proton transfer in (de)hydrogenation processes. • Steric and electronic effects of phosphines on the reactivity. • Reactivity of palladium, nickel, iridium and rutenium pincer hydrides. Transition-metal hydride complexes are plenteous in organometallic chemistry. The reactivity of metal hydrides is determined by three possible pathways of M–H bond cleavage: homolytic cleavage yielding a hydrogen radical (H ), and heterolytic cleavage generating either a proton (H + ) or hydride (H − ). These steps, especially the proton and hydride transfer, are critical in a vast array of stoichiometric and catalytic transformations. Many late transition metal hydrides are supported by phosphine ligands, which allow tuning the electronic and steric properties at a metal center in a systematic and predictable way. In this non-exhaustive review we attempt to trace the influence of phosphines properties on the reactivity of transition metal hydrides in topical stoichiometric and catalytic processes highlighting the reactions’ mechanisms and the role of hydrogen bonding interactions in the intermediates of hydrogen transfer reactions.