An Air Stable Carbene and Mixed Carbene “Dimers”

The air-stable crystalline carbene 1,3-dimesityl-4,5-dichloroimidazol-2-ylidene (2) is produced from the chlorination of 1,3-dimesityimidazol-2-ylidene (1) by 2 equiv of carbon tetrachloride. The physical and spectroscopic properties of the carbene are reported. The features which contribute to the exceptional stability of the carbene are discussed. Further reaction of 2 with carbon tetrachloride leads to reduction of CCl4 to dichlorocarbene. The formation of the mixed carbene “dimers” (olefins) from in situ generated dichlorocarbene and various imidazol(in)-2-ylidenes is also reported. The tellurones derived from 1 and 2 are synthesized and compared.