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 v(CO) and v(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. (C) 2000 Elsevier Science S.A.