A tris(trifluoromethyl)antimony adduct of a nucleophilic carbene: Geometric distortions in carbene adducts

The synthesis, characterization and solid state structure are described for a reversed ylide, derived from 1,3-dimesityl-4,5-dichloroimidazol-2-yliden e and tris(trifluoromethyl)antimony. This carbene stibine adduct is the fir st example of the 10-Sb-4 bonding arrangement in which only carbons are bou nd to antimony. The adduct has an Sb-C-(carbene) bond length of 282.1 pm, a nd a remarkable offset (19 degrees) of the Sb-C-(carbene) bond from the pse udo-C-2 axis which passes through the imidazole fragment. A rather weak ant imony-carbene interaction is suggested by this geometric distortion and is further supported by variable temperature F-19 NMR experiments and solvent dependencies of chemical shifts.