Atom-Efficient Catalytic Coupling of Imidazolium Salts with Ethylene Involving Ni−NHC Complexes as Intermediates:  A Combined Experimental and DFT Study

The coupling reaction between azolium salts (N-heterocyclic carbene precursors) and ethylene, catalyzed by zerovalent nickel complexes, has been investigated using a combination of experiment and density functional theory (DFT). The reaction proceeds via a redox mechanism involving the generation of Ni−carbene intermediates. The experimental studies employed an in situ catalyst system, derived from Ni(COD)2 and a variety of phosphine and N-heterocyclic carbene spectator ligands, to couple 1-propyl-3-methylimidazolium bromide (ionic liquid) and other azolium salts with ethylene. The DFT studies employed the simpler dimethylimidazolium salt to model the reaction.