Oxidative Coupling in the Reaction of TpMe2Ir(2,3-dimethylbutadiene) with Diphenylacetylene

The 2,3-dimethylbutadiene complex TpMe2Ir(CH2C(Me)C(Me)CH2) (1) reacts with PhC⋮CPh, in C6H12 at 60 °C, with coupling of the diene and the alkyne and formation of compound 2a, which contains an elaborated bicyclic chelating ligand with alkyl and η3-allyl functionalities. NCMe reacts reversibly with 2a, giving rise to a mixture of the isomeric iridacyclopentenes (3) and (4). Complex 2a decomposes in C6H12 at 80 °C to give a complex mixture from which an interesting substituted iridafulvene, 5, has been isolated by chromatography. All these compounds have been characterized by NMR spectroscopy and X-ray crystallography. Possible reaction mechanisms for the formation of these species are discussed.