Investigating the mechanism of Ni-mediated trifluoromethylthiolation of aryl halides using AgSCF3

Abstract

The mechanism of the Ni-catalysed trifluoromethylthiolation of aryl chlorides using AgSCF₃ is studied herein. A variety of IPr Ni^II complexes were synthesized via oxidative addition of Ni⁰ to 2-(2-chloro)phenylpyridines. Their reactivity with AgSCF₃ was tested by performing stoichiometric experiments, cyclic voltammetry, and NMR spectroscopic studies. CuSCF₃ was shown to behave similarly to AgSCF₃, while reactions with NMe₄SCF₃ revealed a major stoichiometric side reaction that forms a nickel fluoride complex. NMR kinetic studies revealed there is little correlation between the electron-withdrawing/donating nature of the para substituents on either the phenyl or pyridyl groups with the formation of the corresponding products. Cyclic voltammetry (CV) indicated the feasibilty of Ni^I/Ni^III transitions, and an increased rate of formation of product was observed with increased solvent polarity. Evidence suggests that the mechanism proceeds via inner-sphere electron transfer (ET) from AgSCF₃ to Ni^II, ultimately leading to the formation of the trifluoromethylthiolated product.