Acid-Base Interaction between Transition-Metal Hydrides: Dihydrogen Bonding and Dihydrogen Evolution

摘要

Unconventional hydrogen bonding that involves transition-metal complexes has attracted considerable attention and several efforts have been made to unravel and rationalize the many conceivable interactions. Core transition metals are able to accept a hydrogen bond through their d-electron lone pairs, thus forming M—HA hydrogen bonds whereas hydride ligands that possess a partial negative charge are unusual proton-accepting sites that form a dihydrogen bond (DHB), M-H~(δ-)···~(δ+)HA. The simultaneous presence of both types of bonds was also observed. On the other hand, the reactivity of transition-metal hydrides as proton source is also well appreciated,and hydrogen bonds of the M-H~(δ+)···B type (B = organic base) were recently pointed out for neutral transition-metal hydrides. However, DHB interactions where transition metal hydride complexes serve as both proton acceptor and proton donor in a hydrogen bond have not been described to date, although dihydrogen evolution was observed when "hydridic" and "acidic" hydride complexes such as [OsH2(PMePh2)4]/[CpM(H)(CO)3] system (Cp = η~5-C5H?_5~-, M = Mo, W) were allowed to react.