The binuclear complex [Ir2(CH3)(CO)(μ-CO)(dppm)2][CF3SO3] (1; dppm = μ-Ph2PCH2PPh2) reacts with allene and methylallene to ultimately yield the vinylcarbene products [Ir2H(CO)2(μ-η1:η3-HCC(CH3)C(H)R)(dppm)2][CF3SO3] (R = H (6), CH3 (7)). Monitoring the reactions by NMR spectroscopy (1H, 13C, 31P) between −78 °C and ambient temperature allows the observation of several intermediates in each of these transformations in which the allene moves from an η2 binding site on one metal, through an η1:η1-bridging geometry in which the cumulene is coordinated through the “H2CC” moiety, to an η1:η3-bridging geometry in which the central carbon of the cumulene is σ-bound to one metal, adjacent to the methyl ligand, while the three cumulene carbons are η3-bound to the adjacent metal. We propose that formation of the respective vinyl carbene products results from migration of the methyl ligand to the central cumulene carbon followed by activation of a cumulene C−H bond. 1,1-Dimethylallene reacts with 1 at −78 °C to yield a methylene hydride product containing an η2-bound cumulene on one metal, much as observed for the first products in the allene and methylallene reactions. Upon warming, this intermediate isomerizes to the final product containing a methyl ligand on one metal and an η2-bound cumulene on the other. No cumulene-bridged products are observed with this disubstituted allene. 1,1-Difluoroallene also yields a methylene hydride product at −78 °C, which is analogous to the first species observed in all cases noted above. In this case, warming results in movement of the cumulene to an η1:η1-bridging position in which this group binds to the metals via the “H2CC” moiety. Unlike the transformations observed with allene and methyl allene, difluoroallene undergoes no additional transformations as the temperature is raised. A rationalization of these transformations is presented together with a perspective on how the cumulene ligand moves over the dimetallic framework leading to the final products.

The reactions of the diiridium methyl complex [Ir 2 (CH 3 )(CO)(µ-CO)(dppm) 2 ][CF 3 SO 3 ] (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 [Ir 2 H(η 2 -C 2 H 4 )(CO) 2 (µ-CH 2 )(dppm) 2 ][CF 3 SO 3 ] (2a), resulting from C-H activation of the methyl group induced by ethylene coordination, whereas reaction at higher temperatures yields the simple ethylene adduct [Ir 2 (CH 3 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 [Ir 2 H(η 2 -C 2 F 2 H 2 )(CO) 2 (µ-CH 2 )(dppm) 2 ][CF 3 SO 3 ] (5a), which upon warming, yields first the olefin adduct [Ir 2 (CH 3 ). Trifluoro-and tetrafluoroethylene yield only the olefin-bridged products [Ir 2 7)). The structure of the tetrafluoroethylene-bridged, tricarbonyl species [Ir 2 (CH 3 )(CO) 3 (µ-C 2 F 4 )(dppm) 2 ][CF 3 SO 3 ] (8), determined by X-ray techniques, is reported.

The binuclear complex [Ir2(CH3)(CO)2(dppm)2][CF3SO3] (1) (dppm = Ph2PCH2PPh2) reacts with 1,3-butadiene at ambient temperature over a 48 h period to give the vinylvinylidene-bridged product [Ir2(CH3)(H)(CO)2(μ-H)(μ-CC(H)C(H)CH2)(dppm)2][CF3SO3] (2). At −55 °C the same reactants yield the 1,3-butadiene adduct [Ir2(CH3)(CO)2(μ-η2:η2-H2CC(H)C(H)CH2)(dppm)2][CF3SO3] (3), in which the diolefin binds in an s-trans geometry on one face of the complex. A proposal is advanced rationalizing the conversion of 3 to 2 upon warming.

The bridging fluoroolefin ligands in the complexes [Ir(2)(CH(3))(CO)(2)(μ-olefin)(dppm)(2)][OTf] (olefin = tetrafluoroethylene, 1,1-difluoroethylene; dppm = μ-Ph(2)PCH(2)PPh(2); OTf(-) = CF(3)SO(3)(-)) are susceptible to facile fluoride ion abstraction. Both fluoroolefin complexes react with trimethylsilyltriflate (Me(3)SiOTf) to give the corresponding fluorovinyl products by abstraction of a single fluoride ion. Although the trifluorovinyl ligand is bound to one metal, the monofluorovinyl group is bridging, bound to one metal through carbon and to the other metal through a dative bond from fluorine. Addition of two equivalents of Me(3)SiOTf to the tetrafluoroethylene-bridged species gives the difluorovinylidene-bridged product [Ir(2)(CH(3))(OTf)(CO)(2)(μ-OTf)(μ-C=CF(2))(dppm)(2)][OTf]. The 1,1-difluoroethylene species is exceedingly reactive, reacting with water to give 2-fluoropropene and [Ir(2)(CO)(2)(μ-OH)(dppm)(2)][OTf] and with carbon monoxide to give [Ir(2)(CO)(3)(μ-κ(1):η(2)-C≡CCH(3))(dppm)(2)][OTf] together with two equivalents of HF. The trifluorovinyl product [Ir(2)(κ(1)-C(2)F(3))(OTf)(CO)(2)(μ-H)(μ-CH(2))(dppm)(2)][OTf], obtained through single C-F bond activation of the tetrafluoroethylene-bridged complex, reacts with H(2) to form trifluoroethylene, allowing the facile replacement of one fluorine in C(2)F(4) with hydrogen.

The fluorovinyl complexes [Ir2(CFCF2)(CH3)(CO)2(μ-Cl)(dppm)2][CF3SO3] (2) and [Ir2(C(H)CF2)(CH3)(CO)2(μ-Br)(dppm)2][CF3SO3] (3) are prepared by the oxidative addition of ClFCCF2 and BrHCCF2, respectively, to [Ir2(CH3)(CO)2(dppm)2][CF3SO3] (1). Both compounds have the methyl and fluorovinyl groups on different metals essentially opposite the metal−metal bond. Protonation of 2 occurs at the Ir−Ir bond to give [Ir2(CFCF2)(CH3)(CO)2(μ-Cl)(μ-H)(dppm)2][CF3SO3]2 (4). Attempts to remove the chloride ligand from 2 or to replace it with hydride or methyl groups failed. Instead, the reaction of 2 with methyllithium resulted in replacement of one fluoride substituent on the trifluorovinyl group by a methyl group to give [Ir2(CFCFCH3)(CH3)(CO)2(μ-Cl)(dppm)2][CF3SO3] (5). The X-ray structural determination of 5 indicates that replacement of a fluoride trans to the Ir−C2F3 bond has occurred and that migration of the resulting methyldifluorovinyl group to the metal bearing the methyl ligand has occurred. A proposal is put forth to rationalize these observations.