C-H bond activation and C-C fond formation in the reactions of the methyl complex [Ir2(CH3)(CO)2(Ph2PCH2PPh2)2][CF3SO3] with alkynes

The methyl complex [Ir-2(CH3)(CO)(mu-CO)(dppm)(2)][CF3SO3] (1) reacts readily with a variety of alkyne molecules. With alkynes containing electron-withdrawing substituents (RC=CR'; R = R' = CO2Me, CF3; R = CO2Me, R' = H), the alkyne-bridged products, [Ir-2(CH3)(CO)(2)(mu-alkyne)(dppm)(2)][CF3SO3], result. With other 1-alkynes (HC=CR, R = Me, Ph) reaction at -80 degrees C results in oxidative addition to give acetylide hydrides [Ir2H(CH3)(CO)(2)(mu-C2R)(dppm)(2)][CF3SO3], which upon warming undergo transfer of the hydride ligand to the beta-carbon of the acetylide to give the vinylidene-bridged products. At ambient temperature methane elimination occurs, yielding the acetylide-bridged "A-frames", [Ir-2(CO)(2)(mu-C2R)-(dppm)(2)][CF3SO3]. Reaction of 1 with 1 equiv of acetylene proceeds through analogous acetylide and vinylidene intermediates; however under carbon monoxide exchange of a vinylidene hydrogen and the methyl ligand occurs to give a methylvinylidene-bridged hydride [Ir-2(H)(CO)(3)(mu-CCHMe)(dppm)(2)][CF3SO3]. Reaction of 1 with an excess of acetylene results in the incorporation of two acetylene molecules, giving [Ir-2(CH3)(C2H(CO)(2)(mu-H)(mu-CCH2)(dppm)(2)][CF3SO3], containing terminal methyl and acetylide ligands and bridging hydride and vinylidene groups. Reaction of 1 with a number of internal, nonactivated alkynes results first in the formation of the alkyne-bridged products, which slowly rearrange to the unusual species [Ir2H(CO)(2)(mu-CHCRC(H)R)(dppm)(2)][CF3SO3], in which cleavage of two C-H bonds of the methyl group has occurred accompanied by condensation of the resulting methyne group at one end of alkyne linkage and transfer of a hydrogen to the other end. The resulting hydrocarbyl moiety can be viewed as a vinylcarbene. The X-ray structures of three representative products are reported, including one of these vinylcarbenes (R = C2H5).