C–S couplings catalyzed by Ni(II) complexes of the type [(NHC)Ni(Cp)(Br)]

Abstract

The catalytic activities of three Ni(II) complexes with fluorinated and non–fluorinated N–heterocyclic carbene (NHC) ligands were evaluated in the C–S cross–coupling reaction between iodobenzene and thiophenol. The complexes with fluorinated–NHC ligands exhibited lower catalytic activities compared to the non–fluorinated derivative. This can be attributed to the lower electron–donating character of the fluorinated ligands in comparison to the non–fluorinated ligand. Complex 3–Ni was tested towards different substrates, achieving moderate to good conversions. Additionally, the reaction mechanism of the C–S cross–coupling using two substrates, tert–butylthiol and 2,4–dichlorobenzenethiol, was determined. Tert–butylthiol produced a stable intermediate that inhibited the last step of the reaction mechanism (reductive elimination). On the other hand, 2,4–dichlorobenzenethiol formed a less stable intermediate, favoring the reductive elimination. This observation aligns with the lower yield observed when using tert–butylthiol compared to 2,4–dichlorobenzenethiol (20% vs 99%)