Kinetic and other studies on oxidative addition reactions of iridium phosphine complexes of the type trans-[IrCl(CO)(PMe2R)2](R = Ph, o-MeO·C6H4, or p-MeO·C6H4)

Abstract

Oxidative addition reactions of the new complexes trans-[IrCl(CO){PMe₂(o-MeOC₆H₄)}₂] and trans-[IrCl(CO){PMe₂(p-MeOC₆H₄)}₂] have been compared with those of trans-[IrCl(CO)(PMe₂Ph)₂]; the PMe₂(o-MeOC₆H₄) complex reacted much faster than the other two. Activation parameters have been calculated from kinetic studies of the reactions of the three complexes with methyl iodide in toluene. All three complexes give similarly large negative ΔS‡ values and the ΔH‡ value for the PMe₂(o-MeOC₆H₄) complex is considerably less by (18·8 kJ mol^–1) than that for the PMe₂Ph complex. This difference is interpreted in terms of a direct electronic interaction between the methoxyl oxygen and the iridium; this type of electronic effect has not been observed previously in oxidative addition reactions. The reactions of the three complexes with acetic acid and with benzoic acid have been compared. N.m.r. and i.r. data are given.