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 [Bu 4 N]X (X = Br, I, BF 4 ) as ionic liquid afforded novel square-planar nickel(II) bis(benzimidazolin-2-ylidene) complexes of the general formula trans- [NiX 2 (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.