Solvated Nickel Complexes as Stoichiometric and Catalytic Perfluoroalkylation Agents*.

Abstract

The acetonitrile-solvated [(MeCN)Ni(C2 F5 )3 ]- was prepared in order to compare and contrast its reactivity with the known [(MeCN)Ni(CF3 )3 ]- towards organic electrophiles. Both [(MeCN)Ni(CF3 )3 ]- and [(MeCN)Ni(C2 F5 )3 ]- successfully react with aryl iodonium and diazonium salts as well as alkynyl iodonium salts to give fluoroalkylated organic products. Electrochemical analysis of [(MeCN)NiII (C2 F5 )3 ]- suggests that, upon electro-oxidation to [(MeCN)n NiIII (C2 F5 )3 ], reductive homolysis of a perfluoroethyl radical occurs, with the concomitant formation of [(MeCN)2 NiII (C2 F5 )2 ]. Catalytic C-H trifluoromethylations of electron-rich arenes were successfully achieved using either [(MeCN)Ni(CF3 )3 ]- or the related [Ni(CF3 )4 ]2- . Stoichiometric reactions of the solvated nickel complexes reveal that "ligandless" nickel is exceptionally capable of serving as reservoir of CF3 groups under catalytically relevant conditions.