Olefin Binding in a Binuclear Iridium Complex as a Function of Fluorine Substitution:  Ethylene to Tetrafluoroethylene

The reactions of the diiridium methyl complex [Ir2(CH3)(CO)(μ-CO)(dppm)2][CF3SO3] (1) with ethylene, fluoroethylene, Z -1,2-difluoroethylene, 1,1-difluoroethylene, trifluoroethylene, and tetrafluoroethylene have been investigated. Reaction of 1 with ethylene at −78 °C yields [Ir2H(η2-C2H4)(CO)2(μ-CH2)(dppm)2][CF3SO3] (2a), resulting from C−H activation of the methyl group induced by ethylene coordination, whereas reaction at higher temperatures yields the simple ethylene adduct [Ir2(CH3)(CO)(η2-C2H4)(μ-CO)(dppm)2][CF3SO3] (2b). Reactions of 1 with fluoroethylene and Z -1,2-difluoroethylene yield only the olefin adducts analogous to 2b. At −78 °C reaction with 1,1-difluoroethylene yields the methylene-bridged hydride product [Ir2H(η2-C2F2H2)(CO)2(μ-CH2)(dppm)2][CF3SO3] (5a), which upon warming, yields first the olefin adduct [Ir2(CH3)(CO)(η2-C2F2H2)(μ-CO)(dppm)2][CF3SO3] (5b) followed by the olefin-bridged product [Ir2(CH3)(CO)2(μ-C2F2H2)(dppm)2][CF3SO3] (5c). Trifluoro- and tetrafluoroethylene yield only the olefin-bridged products [Ir2(CH3)(CO)2(μ-olefin)(dppm)2][CF3SO3] (olefin = C2F3H (6), C2F4 (7)). The structure of the tetrafluoroethylene-bridged, tricarbonyl species [Ir2(CH3)(CO)3(μ-C2F4)(dppm)2][CF3SO3] (8), determined by X-ray techniques, is reported.