Synthesis, Structure, and Solution Dynamic Behavior of Nickel Complexes Bearing a 1,3-Diallyl-Substituted NHC Ligand

Reaction of 1,3-diallylimidazolium bromide with 1,1′-dimethylnickelocene (NiCp′2) afforded [NiCp′(all2-NHC)]+Br– (1a) (all2-NHC = 1,3-diallylimidazol-2-ylidene) and NiCp′(all2-NHC)Br (1b), while the reaction of 1,3-diallylimidazolium chloride with nickelocene gave NiCp(all2-NHC)Cl (2) and [NiCp(all2-NHC)2]+Cl– (3). Molecular structures of all four complexes have been established by single-crystal X-ray diffraction. 1H NMR spectra of 1b indicated hindered rotation about the Ni–carbene bond at room temperature, which resulted in the nonequivalence of N–CH2 protons. For compounds 2 and 3 the spectra were dynamic at room temperature and the nonequivalence of N–CH2 protons appeared at low temperature. These observations were confirmed by DFT calculations.