A specific formation of an iridium(III) hydrido complex bearing 8-(diphenylphosphino)quinoline

A reaction of [Cp*IrCl(Ph₂Pqn)]PF₆ {Cp* = η⁵-pentamethylcyclopentadienyl; Ph₂Pqn = 8-(diphenylphosphino)quinoline} and Ag(CF₃SO₃) in methanol afforded orange crystals of the corresponding hydrido complex, [Cp*IrH(Ph₂Pqn)]PF₆, which was identified by ¹H, ³¹P{¹H} NMR and IR spectroscopy as well as X-ray structural analysis. The reactions in deuterated solvents indicated that formation of the hydrido complex proceeded via β-hydrogen elimination of the coordinated methanol molecule. It was also revealed that the hydrido formation was specific for the complex bearing Ph₂Pqn ancillary ligand; the analogous complex with 1,2-bis(diphenylphosphino)benzene (diphos) or 1,10-phenanthroline (phen) did not give the corresponding hydrido complex by a similar reaction with Ag⁺ in methanol. In order to elucidate the reason for the different reactivity among these complexes, the crystal structures of the precursor chlorido complexes, [Cp*IrCl(Ph₂Pqn)]PF₆, [Cp*IrCl(diphos)]PF₆ and [Cp*IrCl(phen)]PF₆, as well as an acetonitrile complex of [Cp*Ir(Ph₂Pqn)(CH₃CN)](PF₆)₂, were also determined by X-ray analysis. The resulting structural information suggested that a specific formation of the hydrido complex with Ph₂Pqn could be originated from the facile formation of the corresponding methanol complex and the hemilabile nature of ancillary Ph₂Pqn ligand, which induced the reactivity of the coordinated methanol toward β-hydrogen elimination.