Towards Nickel-NHC Fluoro Complexes-Synthesis of Imidazolium Fluorides and Their Reactions with Nickelocene.

While hundreds of complexes of the general formula [Ni(η-CH)(NHC)(X)] exist (NHC = a N-heterocyclic carbene, X = Cl, Br, I), none is yet known with X = F. We attempted to prepare such a species by reacting nickelocene with imidazolium fluorides. Three imidazolium fluorides (ImH) F [Im = (,'-(R)-imidazolium: , IMe, R = Me; , IMes, R = 2,4,6-trimethylphenyl; , IPr, R = 2,6-diisopropylphenyl)] were prepared and characterized by spectroscopic methods. In addition, the salts [(IMesH) F] and [(IPrH) F] were subjected single-crystal X-ray diffraction experiments. The reactions of these imidazolium fluorides with nickelocene did not lead to [Ni(η-CH)(NHC)(F)] species. Instead, the reaction of [(IMeH) F] and [(IMesH) F] with nickelocene led to the salt [Ni(η-CH)(IMe)] F and to the square planar complex [NiF(IMes)] respectively. Both complexes were characterized spectroscopically and by single crystal X-ray diffraction. All four X-ray diffraction studies reveal hydrogen bonding and hydrogen interactions with the F atom or anion, and in some cases with solvent molecules of crystallization, and these phenomena are all discussed. Complex , in particular, exhibited a wide range of interesting H-bonded interactions in the solid state. Complexes and were tested as catalysts for Suzuki-Miyaura coupling but were not promising: complex was inactive, and while did indeed catalyze the reaction, it gave widely diverging results owing to its instability in solution.