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 voltammet ric conditions, the process IrH(CO)(PPh3)(3) reversible arrow [IrH(CO)(PPh3 )(3)](+) + e(-), which leads to the formation of the 17-electron [IrH(CO)(P Ph3)(3)](+) cation, is chemically and electrochemically reversible. In cont rast, the 16-electron dication [IrH(CO)(PPh3)(3)](2+), formed by a further one-electron oxidation process, is very reactive and undergoes a rapid inte rnal redox reaction, [IrH(CO)(PPh3)(3)](2+) reversible arrow [Ir(CO)(PPh3)( 3)](+) + H+, to form the stable 16-electron [Ir(CO)(PPh3)(3)](+) species. I n situ infrared (IR) spectroelectrochemical studies at low temperature, ena ble the nu(CO) and nu(IrH) IR bands to be obtained for [IrH(CO)(PPh3)(3)]() as well as for transiently formed [IrH(CO)(PPh3)(3)](2+). EPR spectra obt ained 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 struct ure. Data are compared with those available for oxidation of the analogous RhH(CO)(PPh3)(3) complex. (C) 2000 Elsevier Science S.A. All rights reserve d.