Oxidative additions to nitrosyltris(triphenylphosphine)iridium(-I). Five-co-ordinate methyl–nitrosyl and hydrido–nitrosyl derivatives of iridium(I)

Abstract

A convenient preparation of [Ir(NO)(PPh₃)₃], from the readily available compound, [IrCl(CO)(PPh₃)₂], is described. There is a resemblance between its reactivity and that of the isoelectronic platinum compound [Pt(PPh₃)₄], [Ir(NO)(PPh₃)₃] reacts with halogens to from the five-co-ordinate series, [IrX₂(NO)(PPh₃)₂](X = Cl, Br, or I) while reaction with iodomethane produces the methyl–iridium compound [IrMe(I)(NO)(PPh₃)₂]. These compounds are monomeric in benzene and in the solid state have a tetragonal pyramidal structure with a bent nitrosyl group at the apex. Hydrogen halides in stoicheiometric amounts also produce [IrX₂(NO)(PPh₃)₂] but reaction of [Ir(NO)(PPh₃)₃] with an excess of hydrogen chloride or bromide results in a novel ligand reaction in which the nitrosyl group is converted to bound hydroxylamine to give [IrCl₃(NH₂OH)(PPh₃)₂] and [IrBr₃(NH₂OH)(PPh₃)₂]. The corresponding ammonia complex [IrCl₃(NH₃)(PPh₃)₂] has been prepared by an independent route for comparison. Protonation with non-complexing acids produces [IrH(NO)(PPh₃)₃]Y (Y = ClO₄, BF₄, or PF₆) which exist in two or more different crystalline forms; some of these have different physical properties and are probably isomers. The protonation is reversed by the action of bases, and lithium halides convert the hydrido-cation to the neutral hydrido–nitrosyls [IrHX(NO)(PPh₃)₂](X = Cl, Br, or I). I.r. spectra are reported and the nitrosyl stretching frequencies correlated with the various types of nitrosyl group found in these compounds.