Synthesis and Structural Characterization of the First Bis(benzimidazolin-2-ylidene) Complexes of Nickel(II)

The reaction of Ni(OAc)₂ with the benzimidazolium salts 1,3-dimethylbenzimidazolium iodide (1), 1,3-bis(2-propenyl)benzimidazolium bromide (2), 1,3-dipropylbenzimidazolium bromide (3), 1-(2-propenyl)-3-methylbenzimidazolium bromide (6), and 1-propyl-3-methylbenzimidazolium iodide (7) in molten [Bu₄N]X (X = Br, I, BF₄) as ionic liquid afforded novel square-planar nickel(II) bis(benzimidazolin-2-ylidene) complexes of the general formula trans-[NiX₂(NHC)₂] (X = I, NHC = 1,3-dimethylbenzimidazolin-2-ylidene, 8; X = Br, NHC = 1,3-bis(2-propenyl)benzimidazolin-2-ylidene, 9; X = Br, NHC = 1,3-dipropylbenzimidazolin-2-ylidene, 10; X = Br, NHC = 1-(2-propenyl)-3-methylbenzimidazolin-2-ylidene, 11; X = I, NHC = 1-propyl-3-methylbenzimidazolin-2-ylidene, 12). X-ray diffraction studies of 8−12 reveal a square-planar coordination geometry for all complexes with the carbene ligands arranged in a trans fashion.