Reactivity of the Iridium(I) Alkene/Alkyne Complex Tp^Me2Ir(C₂H₄)(MeO₂CC⋮CCO₂Me)

TpMe2Ir(C2H4)2 (1; TpMe2 = hydrotris(3,5-dimethylpyrazolyl)borate) reacts with 1 equiv of MeO2CC⋮CCO2Me (DMAD) at 25 °C, via the intermediacy of the known Ir(I) adduct TpMe2Ir(C2H4)(DMAD) (2), with formation of the bis(alkenyl) derivative TpMe2Ir(cis-C(R)C(R)H)(CHCH2)(C2H4) (3; R = CO2Me) in ca. 50% yield. Complex 3 slowly evolves to another alkenyl species, (4), which exists as a mixture of two stereoisomers. Interestingly, complex 2 reacts with the hard Lewis base NCMe at −20 °C, giving the Ir(I) adduct TpMe2Ir(DMAD)(NCMe) (5) the first Ir(I) compound of the TpMe2Ir system with a hard ligand. The Ir−NCMe bond in 5 is labile, and the acetonitrile is easily interchanged by CO, C2H4, and the alkynes HC⋮CCO2Me (MP) and DMAD. While with CO the reaction stops at the substitution stage with formation of TpMe2Ir(DMAD)(CO) (8), with C2H4 it gives complex 4 or the bis(alkenyl) species TpMe2Ir(cis-C(R)C(R)H)(CHCH2)(NCMe) (9), depending on the concentration of NCMe in the reaction medium. With MP the known iridacyclopentadiene (10) and the symmetrical iridacycloheptatriene (11) can be obtained, while related iridacycles are formed with DMAD. Finally an iridapyrrole with the composition (6) is the unexpected result of heating complex 5 in a CH2Cl2−NCMe mixture at 120 °C. All of the new compounds reported have been characterized by microanalysis and IR and NMR spectroscopy and, in addition, complexes 4 and 6 have been characterized by single-crystal X-ray studies.