| Sumario: | Density functional theory calculations have been used to model the reaction of CF with [IrMe(PEt)], which proceeds with both C-F and P-C bond activation to yield trans-[Ir(CF)(PEt)(PEtF)], CH, and CH (Blum, O.; Frolow, F.; Milstein, D. J. Chem. Soc., Chem. Commun. 1991, 258). Using a model species, trans-[IrMe(PH)(PHEt)], a low-energy mechanism involving nucleophilic attack of the electron-rich Ir metal center at CF with displacement of fluoride has been identified. A novel feature of this process is the capture of fluoride by a phosphine ligand to generate a metallophosphorane intermediate [Ir(CF)(Me)(PH)(PHEtF)]. These events occur in a single step via a 4-centered transition state, in a process that we have termed "phosphine-assisted C-F activation". Alternative mechanisms based on C-F activation via concerted oxidative addition or electron-transfer processes proved less favorable. From the metallophosphorane intermediate the formation of the final products can be accounted for by facile ethyl group transfer from phosphorus to iridium followed by β-H elimination of ethene and reductive elimination of methane. The interpretation of phosphine-assisted C-F activation in terms of nucleophilic attack is supported by the reduced activation barriers computed with the more electron-rich model reactant trans- [IrMe(PMe)(PMeEt)] and the higher barriers found with lesser fluorinated arenes. Reactivity patterns for a range of fluoroarenes indicate the dominance of the presence of ortho-F substituents in promoting phosphine-assisted C-F activation, and an analysis of the charge distribution and transition state geometries indicates that this process is controlled by the strength of the Ir-aryl bond that is being formed.
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