Structural assignment of the stable carbonylhydridotris-(triphenylphosphine)iridium(II) cation and spectroscopic and voltammetric identification of the transient Ir(III) dication and its decomposition pathway

Detailed studies on the electrochemical oxidation of the 18-electron IrH(CO)(PPh3)3 complex have been undertaken in dichloromethane. Under voltammetric conditions, the process IrH(CO)(PPh3)3⇌[IrH(CO)(PPh3)3]++e−, which leads to the formation of the 17-electron [IrH(CO)(PPh3)3]+ cation, is chemically and electrochemically reversible. In contrast, the 16-electron dication [IrH(CO)(PPh3)3]2+, formed by a further one-electron oxidation process, is very reactive and undergoes a rapid internal redox reaction, [IrH(CO)(PPh3)3]2+⇌[Ir(CO)(PPh3)3]++H+, to form the stable 16-electron [Ir(CO)(PPh3)3]+ species. In situ infrared (IR) spectroelectrochemical studies at low temperature, enable the ν(CO) and ν(IrH) IR bands to be obtained for [IrH(CO)(PPh3)3]+ as well as for transiently formed [IrH(CO)(PPh3)3]2+. EPR spectra obtained from frozen solutions of electrochemically generated [IrH(CO)(PPh3)3]+ have been simulated. In agreement with results of density functional calculations on related IrX(CO)(PPh)3 (X=H, Cl) complexes, the EPR data are consistent with [IrH(CO)(PPh3)3]+ having a square pyramidal structure. Data are compared with those available for oxidation of the analogous RhH(CO)(PPh3)3 complex.