The relative rates of neutral ligand exchange reactions in some complex iridium(III) hydrides and halides. Iridium(III) hydrido- and halogeno-complexes containing two different tertiary phosphine and/or tertiary arsine ligands

Abstract

The tertiary phosphine or tertiary arsine ligands (L) in trans-position to hydride in complexes of the type [lrHCl₂L₃] configuration (I), is labile towards substitution by the strongly bonding phosphine, PMe₂Ph, the other two neutral ligands (L) being inert. Complexes of the type [lrHCl₂L₂(PMe₂Ph)], configuration (II)(L = tertiary phosphine or tertiary arsine; X = Cl), can thus be readily prepared. The reaction goes through a dissociative mechanism, being independent of PMe₂Ph concentration. The relative rates of substitution of the ligand L (studied by a ¹H n.m.r. method) are in the order L = AsEt₃ PEt₃ > PBuⁿ₃ PEt₂Ph > PBu₂Ph, and substitution is faster in [lrHBr₂(PEt₃)₃] than in [lrHCl₂(PEt₃)₃]. The monohydride-complex [lrHCl₂(PEt₂Ph)₃], configuration (III), undergoes general displacement of the PEt₂Ph ligands by PMe₂Ph but the dihydrido-complexes [lrH₂X(PEt₂Ph)₃][X = Cl, Br, or l] are inert to substitution by PMe₂Ph. Treatment of complexes of the type mer-[IrCl₃Ars₃](Ars = AsEt₃ or AsEt₂Ph) with PMe₂Ph gave complexes of the type [IrCl₃(Ars)(PMe₂Ph)₂], configuration (VI), but similar treatment of the corresponding phosphine complexes mer-[IrCl₃Phos₃](Phos = PEt₃ or PEt₂Ph) gave complexes of type [IrCl₃(Phos)(PMe₂Ph)₂], configuration (VII). Infrared and n.m.r. data are given and discussed.