Low-Valent Transition-Metal Hydride Complexes as Alternatives to Lewis Acid and Base Catalysts
Shun-Ichi Murahashi
Department of Chemistry,
Graduate School of Engineering Science, Osaka University,
1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan
Lewis acid- and base-promoted reactions are fundamental reactions in organic chemistry; however, the majority of these reactions are still stoichiometric reaction and require disposal of chemical wastes after reaction. Salts are the main waste, accounting for 70% by weight. Therefore, the development of catalytic alternatives that use transition-metal complex under neutral and mild conditions is particularly important; society needs forward-looking technology, which is based on environmental acceptability.
By designing Lewis acid and base catalysts bearing low redox potentials, which we call redox Lewis acid and base catalysts, one can carry out these reactions catalytically under neutral conditions. By systematic study for searching such catalysts, we found that low-valent transition-metal hydride complexes are excellent catalysts as both Lewis acid and base catalysts towards activation of nitriles and carbonyl compounds, and reactions promoted by conventional Lewis acids or bases can be replaced by catalytic reactions under neutral conditions.