title: A (pentafluoroethyl)(trifluoromethyl)carbene complex of iridium and reductive activation of its sp(3)α, β, and γ carbon-fluorine bonds to give perfluoro-2-butyne, perfluoro-1,2,3-butatriene and perfluoro-1-irida-2-methyl-2-cyclobutene) complexes.
abstract: The (pentafluoroethyl)(trifluoromethyl)carbene complex Cp*Ir(CO)[[double bond, length as m-dash]C(CF3)(C2F5)] was synthesized by the reductive activation of the α-C-F bond in the perfluoro-sec-butyl-iridium complex Cp*Ir(CO)[CF(CF3)(C2F5)](I) with Na/Pb alloy. This compound exists as two geometric isomers in solution; the structure of one isomer has been determined by a single crystal X-ray diffraction study and contains two independent molecules in the asymmetric unit. Further reduction of this carbene complex with Na/Pb alloy afforded the perfluoro-2-butyne iridium complex Cp*Ir(CO)(η(2)-CF3C[triple bond, length as m-dash]CCF3) by an overall 2-electron reduction and elimination of two β-fluorides. When magnesium graphite was utilized as the reducing agent for the further reduction, Cp*Ir(CO)(η(2)-CF3C[triple bond, length as m-dash]CCF3) was produced as a minor product and the major product was the perfluoroiridacyclobutene complex Cp*Ir(CO)(η(2,4)-CF3CCFCF2) resulting from a γ-C-F bond activation. Direct reduction of the precursor Cp*Ir(CO)[CF(CF3)(C2F5)](i) with magnesium graphite generated the tetrafluorobutatriene iridium complex Cp*Ir(CO)(η(2,3)-CF2[double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]CF2) along with the perfluoro-2-butyne complex and perfluoroiridacyclobutene complexes in a ratio of 1 : 2 : 6. These reductive inner-sphere pathways to unsaturated fluorocarbon ligands illustrate that carbon-fluorine bond activation can take place at α-, β- and γ-carbons but that selectivity in these heterogeneous reductions is difficult to control, with a variety of fluoride eliminations possible for complex perfluoroalkyl ligands. Density Functional Theory (DFT/B3LYP-D3/LACV3P**++) is used to explore the relative energetics of products and intermediates in these reactions.
authors.affiliation: Department of Chemistry, 6128 Burke Laboratory, Dartmouth College, Hanover, New Hampshire 03755, USA. rph@dartmouth.edu.
authors.forename: Jian
authors.initials: J
authors.lastname: Yuan
authors.forename: Russell P
authors.initials: RP
authors.lastname: Hughes
authors.forename: Arnold L
authors.initials: AL
authors.lastname: Rheingold