Deoxyhalogenation with Cu(III) Halide Complexes

While high-valent metal-halide complexes are widely studied as oxidants that promote C-H activation, their Lewis acidic reactivity has received little attention. Herein, we report a new mode of Cu(III) reactivity in which Lewis acidic Cu(III) complexes activate C(sp3)-OH bond in alcohols and convert them to the corresponding alkyl fluorides, chlorides, and bromides. A series of formal Cu(III) halide complexes (X = F, Cl, Br) supported by the tris(2-pyridylthio)methanide (TPTM, L) ligand were synthesized. These trigonal-bipyramidal [LCuIII-X]+ complexes feature an anionic carbon donor trans to the halide, resulting in weakened Cu-X bonds. Unlike conventional Cu(III) complexes that typically promote hydrogen atom abstraction, [LCuIII-X]+ instead activates the C(sp3)-OH bond for deoxyhalogenation. Mechanistic studies suggest that the reaction proceeds through initial activation of the C(sp3)-OH bond by the Lewis acidic CuIII center to generate a carbocation intermediate, which is subsequently trapped by halides to form the C(sp3)-X bond. While Lewis acid-promoted deoxychlorination and deoxybromination reactions have been reported previously, this study represents the first example of a metal complex capable of mediating a general deoxyhalogenation series including F, Cl, and Br transfer.