Reaction of the Iridacyclopentadiene Tp^Me2Ir(C(R)C(R)C(R)C(R))(H₂O) (R = CO₂Me) with Alkynes

The iridacyclopentadiene derivative TpMe2Ir(C(R)C(R)C(R)C(R))(H2O) (1) (TpMe2 = hydrotris(3,5-dimethylpyrazolyl)borate, R = CO2Me) reacts with an excess of MeCCMe with formation of the iridacycloheptatriene TpMe2Ir(C(Me)C(Me)C(R)C(R)C(R)C(R))(H2O) (3) and the first metallabicyclo[3,2,0]heptatriene TpMe2Ir(C(Me)C(Me)C(R)C(R)C(R)C(R))(H2O) (4). Both species are involved in the equilibrium 3 ⇌ 4 + H2O, which has been studied as a function of temperature. By contrast, PhCCPh gives only a compound related to 4, namely, the species TpMe2Ir(C(Ph)C(Ph)C(R)C(R)C(R)C(R))(H2O) (5), which does not react with water. Complex 1 incorporates two molecules of terminal alkynes such as HCCPh and HCCCH2CH2OH with formation of complex chelating alkenyl-allylic structures, and the same is true for Me3SiCCPh and Me3SiCCSiMe3, where the SiMe3 groups are replaced by hydrogen atoms under the reaction conditions. In all these cases the two alkynes are added consecutively into one of the Ir−C bonds of 1. Finally, the reaction of 1 with HCCCO2Me gives a fully substituted cyclopentadiene with two of the substituents being metalated by the iridium center and in this case the two Ir−C bonds of 1 are cleaved in the process. All the new compounds have been characterized by microanalysis, IR and NMR spectroscopies, and in some cases by X-ray diffraction analysis.