A (pentafluoroethyl)(trifluoromethyl)carbene complex of iridium and reductive activation of its sp(3) alpha, beta, and gamma carbon-fluorine bonds to give perfluoro-2-butyne, perfluoro-1,2,3-butatriene and perfluoro-1-irida-2-methyl-2-cyclobutene) complexes

作者：Yuan Jian; Hughes Russell P^*; Rheingold Arnold L

来源：Dalton Transactions, 2015, 44(45): 19518-19527.

DOI：10.1039/c5dt02075a

The (pentafluoroethyl)(trifluoromethyl) carbene complex Cp*Ir(CO)[=C(CF3)(C2F5)] was synthesized by the reductive activation of the alpha-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)(eta(2)-CF3C CCF3) by an overall 2-electron reduction and elimination of two beta-fluorides. When magnesium graphite was utilized as the reducing agent for the further reduction, Cp*Ir(CO)(eta(2)-CF3C=CCF3) was produced as a minor product and the major product was the perfluoroiridacyclobutene complex Cp*Ir(CO)(eta(2,4)-CF3CCFCF2) resulting from gamma-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)(eta(2,3)-CF2=C=C=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 alpha-, beta- and gamma-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.

• 出版日期2015