The Crystal and Molecular Structure of Chlorocarbonyltris (Phenyldimethylphosphine) Iridium (I). Chemical Implications of a Long Iridium-Chlorine Bond

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Abstract
Sir: We have recently reported that the addition of excess PMe2Ph to a solution of IrCl(CO) (PMe2Ph)2 resulted in spectral changes which were interpreted in terms of the formation of the tris(phosphine) complex, IrCl(CO) (PMe2Ph)3 (1).1 The further observation1 that the apparent rate of oxidative addition of H2 to 1 was higher than to IrCl(CO)(PMe2Ph)2 was unexpected in view of prior demonstrations that other five-coordinate d 8 complexes are intrinsically unreactive toward H2 and related substrates, the oxidative additions of such molecules generally being accomplished through mechanisms involving prior dissociation to reactive four-coordinate complexes.2–4 One possible interpretation of this unusual reversal of reactivity is that depicted by equation (1) according to which 1 is in equilibrium, through dissociation of the Cl− ligand, with a highly reactive four-coordinate ion pair [Ir(CO) (PMe2Ph)3]+Cl−.5 In the light of these considerations the isolation of 1 and the determination of its structure by single crystal X-ray diffraction were clearly of interest.