Transformation of a terminal to a bridging carbonyl ligand accompanied by iridium-iridium bond cleavage: an example of transmission of electronic effects from one metal center to another

The alkyne-bridged complex [Ir2Cl2(CO)(μ-DMA)(DPM)2] [DMA = di-Me acetylenedicarboxylate, DPM = bis(diphenylphosphino)methane] reacts with 1 equiv of CO, PMe3, P(OMe)3, or NCMe to give one of two types of species. Reaction with CO yields the complex [Ir2Cl2(CO)2(μ-DMA)(DPM)2], in which both carbonyl groups are terminally bound, one to each metal. However, reaction with L = PMe3, P(OMe)3, or NCMe yields the adduct [Ir2Cl2L(μ-CO)(μ-DMA)(DPM)2], in which the carbonyl group bridges the metals with no accompanying Ir-Ir bond. The long metal-metal sepn. of 3.4580 (7) Å results in a geometry at the bridging carbonyl ligand that is reminiscent of sp2 hybridization [Ir-C(O)-Ir angle of 119.4 (6)°]