Synthesis of Ruthenium Complexes with a Nonspectator Si,O,P-Chelate Ligand: Interconversion between a Hydrido(η2‑silane) Complex and a Silyl Complex Leading to Catalytic Alkene Hydrogenation

A ruthenium complex bearing a new phosphine­(η2-silane) chelate ligand connected by a xanthene backbone, Ru­{κ4(Si,H,O,P)-tBu2xantSiP­(H)}­(H)­Cl­(PPh3) (2), was synthesized by a ligand substitution reaction of Ru­(H)­Cl­(PPh3)3 with 2,7-di-tert-butyl-4-dimethylsilyl-5-diphenylphosphino-9,9-dimethylxanthene (1, tBu2xantSiP­(H)). Dehydrogenation reaction of 2 with styrene, a hydrogen acceptor, gave a 16-electron phosphine­(silyl) complex Ru­{κ3(Si,O,P)-tBu2xantSiP}­Cl­(PPh3) (3) together with ethylbenzene. Complex 2 was reproduced quantitatively by exposure of 3 to H2 (1 atm) at room temperature. Thus, hydrido­(η2-silane) complex 2 and silyl complex 3 are interconvertible through alkene hydrogenation (from 2 to 3) and dihydrogen addition to the Ru–Si bond (from 3 to 2) in which tBu2xantSiP functions as a nonspectator ligand by reversibly releasing and accommodating a hydrogen atom. Complex 2 was also found to catalyze hydrogenation of alkenes via this interconversion.