Pincer Phosphine Complexes of Ruthenium: Formation of Ru(P−O−P)(PPh₃)HCl (P−O−P = xantphos, DPEphos, (Ph₂PCH₂CH₂)₂O) and Ru(dppf)(PPh₃)HCl and Characterization of Cationic Dioxygen, Dihydrogen, Dinitrogen, and Arene Coordinated Phosphine Products

Abstract

Treatment of Ru(PPh(3))(3)HCl with the pincer phosphines 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene (xantphos), bis(2-diphenylphosphinophenyl)ether (DPEphos), or (Ph(2)PCH(2)CH(2))(2)O affords Ru(P-O-P)(PPh(3))HCl (xantphos, 1a; DPEphos, 1b; (Ph(2)PCH(2)CH(2))(2)O, 1c). The X-ray crystal structures of 1a-c show that all three P-O-P ligands coordinate in a tridentate manner through phosphorus and oxygen. Abstraction of the chloride ligand from 1a-c by NaBAr(4)(F) (BAr(4)(F) = B(3,5-C(6)H(3)(CF(3))(2))(4)) gives the cationic aqua complexes [Ru(P-O-P)(PPh(3))(H(2)O)H]BAr(4)(F) (3a-c). Removal of chloride from 1a by AgOTf yields Ru(xantphos)(PPh(3))H(OTf) (2a), which reacts with water to form [Ru(xantphos)(PPh(3))(H(2)O)H](OTf). The aqua complexes 3a-b react with O(2) to generate [Ru(xantphos)(PPh(3))(eta(2)-O(2))H]BAr(4)(F) (5a) and [Ru(DPEphos)(PPh(3))(eta(2)-O(2))H]BAr(4)(F) (5b). Addition of H(2) or N(2) to 3a-c yields the thermally unstable dihydrogen and dinitrogen species [Ru(P-O-P)(PPh(3))(eta(2)-H(2))H]BAr(4)(F) (6a-c) and [Ru(P-O-P)(PPh(3))(N(2))H]BAr(4)(F) (7a-c), which have been characterized by multinuclear NMR spectroscopy at low temperature. Ru(PPh(3))(3)HCl reacts with 1,1'-bis(diphenylphosphino)ferrocene (dppf) to give the 16-electron complex Ru(dppf)(PPh(3))HCl (1d), which upon treatment with NaBAr(4)(F), affords [Ru(dppf){(eta(6)-C(6)H(5))PPh(2)}H]BAr(4)(F) (8), in which the PPh(3) ligand binds eta(6) through one of the PPh(3) phenyl rings. Reaction of 8 with CO or PMe(3) at elevated temperatures yields the 18-electron products [Ru(dppf)(PPh(3))(CO)(2)H]BAr(F)(4) (9) and [Ru(PMe(3))(5)H]BAr(4)(F) (10).