Facile synthesis of half-sandwich (NHC)Ni(Cp)X complexes from labile NHC proligands

A new approach to the one-pot synthesis of a series of nickel(II) complexes of the general formula (NHC)Ni(Cp)X (NHC = N-heterocyclic carbene, Cp = η⁵-coordinated cyclopentadienyl anion, X = Cl, Br) has been developed. The method involves the reaction of N,N'-diarylimidazolium or imidazolinium salt NHC-precursor with nickelocene in the presence of Bu^tOK with subsequent displacement of one Cp ligand in nickel complex by halide anion under the action of HCl or HBr. The method allows one to obtain previously inaccessible complexes with NHC ligands containing alkoxy or RSO₂ groups in the NHC backbone, which are unstable under the usual conditions of synthesis of (NHC)Ni(Cp)X complexes.