The effect of bulky tertiary t-butylphosphine or tertiary di-t-butyl-phosphine ligands, L, on the tendency of complexes trans-[IrX(CO)L2](X = Cl or Br) to undergo oxidative addition reactions
Oxidative addition reactions of sterically hindered complexes of the type trans-[IrX(CO)L2](X = Cl or Br), have been studied. trans-[IrX(CO)(PButMe2)2] adds on a variety of molecules, e.g. Cl2, H2, O2, CCl4, CH2:CH·CH2Cl, AcCl, ClCO2Me, PhN2+Cl–, PhSO2Cl etc. Homologues of the type trans-[IrX(CO)(PButR2)2], (R = Et, Prn or Bun), however, show a greatly reduced tendency to undergo oxidative addition for, although they will react with Cl2, H2, Mel, or O2, they will not add on larger molecules such as CH2:CH·CH2Cl or AcCl. trans-[IrCl(CO)(PBut2Me)2] will add on Cl2 or O2 very slowly but the corresponding adducts with trans-[IrCl(CO)(PBut2R)2](R = Et or Prn) would not form. The complexes trans-[IrCl(CO)L2] react with carbon monoxide in methanol to give the cations [Ir(CO)3L2]+, isolated as the tetraphenylborate salts (L = PButR2; R = Me, Et, Prn or Bun). The configurations of most of the complexes have been determined by i.r. or 1H n.m.r. spectroscopy.