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

Abstract

Oxidative addition reactions of sterically hindered complexes of the type trans-[IrX(CO)L₂](X = Cl or Br), have been studied. trans-[IrX(CO)(PBu^tMe₂)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)(PBu^tR₂)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)(PBu^t₂Me)₂] will add on Cl₂ or O₂ very slowly but the corresponding adducts with trans-[IrCl(CO)(PBu^t₂R)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 = PBu^tR₂; 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.