Iridium complexes featuring a tridentate SiPSi ligand: from dimeric to monomeric 14, 16 or 18-electron species

In the solid state, the dinuclear iridium complex [μ-Cl-Ir(SiMe₂CH₂-o-C₆H₄)₂PPh]₂, 1, is shown by X-ray diffraction to bear dibenzylsilylphosphine ligands in SiPSi tridentate coordination modes as well as chloride bridges. In C₆D₆ solution, 1 dissociates into the 14-electron species [IrCl(SiMe₂CH₂-o-C₆H₄)₂PPh] prone to coordinate one or two L-type ligands such as PR₃ (R = Cy, Ph, OEt), CO and CH₃CN giving rise to the corresponding mononuclear 16- or 18-electron complexes [IrCl(SiMe₂CH₂-o-C₆H₄)₂PPh(L)_x] (x = 1, 2) as evidenced by X-ray and NMR studies. The dinuclear structure is retained upon reaction with Et₃SiH which results in the formation of [μ-Cl,μ-H-Ir₂{(SiMe₂CH₂-o-C₆H₄)₂PPh}₂] with a bridging hydride. On the basis of NMR studies, the reaction of the triphenylphosphine complex [IrCl(SiMe₂CH₂-o-C₆H₄)₂PPh(PPh₃)] with LiBHEt₃ leads to the hydride complex [IrH(SiMe₂CH₂-o-C₆H₄)(η²-H-SiMe₂CH-o-C₆H₄)PPh(PPh₃)] in which one SiPSi ligand has been transformed and is now bonded to iridium in a tetradentate mode via P, Si, an agostic Si-H bond, and C of a methine as a result of the activation of one methylene group.