Approaches to prepare perfluoroalkyl and pentafluorophenyl copper couples for cross-coupling reactions with organohalogen compounds

Abstract

The reactions of iodoperfluoroalkanes C_nF_2n+1I (n = 2, 3, 4) and n-BuLi at low temperatures give NMR spectroscopic evidence for LiC_nF_2n+1 which were converted into LiCu(C_nF_2n+1)₂ derivatives upon treatment with 0.5 mol copper(I) bromide, CuBr. An alternative route to obtain perfluoroorgano copper couples, Cu(R_f)₂Ag (R_f = n-C₃F₇, n-C₄F₉, C₆F₅) was achieved from the reactions of the corresponding perfluoroorgano silver(I) reagents, AgR_f, and elemental copper through redox transmetallations. The composition of the resulting reactive intermediates was investigated by means of ¹⁹F NMR spectroscopy and ESI mass spectrometry. Perfluoro-n-propyl and perfluoro-n-butyl copper–silver reagents prepared by the oxidative transmetallation route exhibited good properties in C–C bond formation reactions with acid chlorides even under moderate conditions. Substitution of bromine directly bound to aromatics for perfluoroalkyl groups was achieved at elevated temperatures, while success in halide substitution reactions using lithium copper couples remained poor.