Tandem C–F and C–H Bond Activation in Fluoroolefins Promoted by a Bis(diethylphosphino)methane-Bridged Diiridium Complex: Role of Water in the Activation Processes
datasetposted on 22.02.2016, 04:58 by Michael E. Slaney, Michael J. Ferguson, Robert McDonald, Martin Cowie
The diiridium complex [Ir2(CO)3(μ-H)(depm)2]+ (1) reacts with vinyl fluoride, 1,1-difluoroethylene, trifluoroethylene, and tetrafluoroethylene, undergoing C–F bond activation in all cases, in addition to C–H activation in the incompletely substituted fluoroolefins. Reaction of 1 with vinyl fluoride readily undergoes geminal C–F/C–H activation, resulting in the bridging vinylidene product, [Ir2(H)(CO)3(μ-CCH2)(depm)2]+ (2). Compound 1 reacts with 1,1-difluoroethylene at subambient temperature to give minor amounts of [Ir2(CO)3(κ1:η2-CCH)(depm)2]+ (4), resulting from the loss of 2 equiv of HF from the fluoroolefin complex, along with a mixture of two isomers of [Ir2(C(F)CH2)(CO)3(μ-CF2CH2)(depm)2]+ (5a/5b), in which 2 equiv of the olefin has been incorporated. Compound 1 also reacts with trifluoroethylene at −30 °C, giving a 1:1 mix of isomers of the trifluoroethylene-bridged species [Ir2(H)(CO)3(μ-CFHCF2)(depm)2]+ (7a/7b), and warming this mixture above −15 °C converts both isomers to two products, [Ir2(H)(CO)3(μ-CCF2)(depm)2]+ (8), in which the geminal C–F and C–H bonds in the fluoroolefin have been activated, and [Ir2(H)(CO)3(μ-CHCF3)(depm)2]+ (9), the result of a [1,2]-fluoride shift to give the bridging 2,2,2-trifluoroethylidene moiety. Compound 9 reacts further with a second equivalent of trifluoroethylene over 12 h to produce the 2,2,2-trifluoroethylidene/cis-difluorovinyl complex, [Ir2(C(F)CFH)(CO)3(μ-CHCF3)(depm)2]+ (10). Finally, tetrafluoroethylene reacts with 1 to produce the bridged adduct, [Ir2(H)(CO)3(μ-CF2CF2)(depm)2]+ (11), followed by a single C–F activation to give [Ir2(C(F)CF2)(CO)3(depm)2]+ (12). The roles of the hydride ligand and exogenous water in the C–F activation processes are discussed.