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.