No abstract

The syntheses and characterizations of homoleptic bis(carbene) adducts of Ag(1) and Cu(1) are described. These carbene adducts are available directly from the reaction of the stable nucleophilic carbene 1,3-dimesitylimidazol-2-ylidene and the corresponding metal triflate. NMR data are consistent with the bis(carbene)metal structures and suggest a level of delocalization in the imidazole ring that is intermediate between those of the free carbene and imidazolium ions. The X-ray crystal structure of the silver-carbene adduct is reported: [ C*2H&&g]CF3-SO3, monoclinic, space group P21/c (No. 14), a = 1167.5(1) pm, b = 1472.9(2) pm, c = 2479.8(2) pm, / 3 = 95.31(1)'; T = -70 OC, 2 = 4. The silver is essentially linearly coordinated with the imidazole rings twisted 39.7' relative to one another. The solid-state structure of the silvercarbene adduct is compared with those of related gold-carbene adducts.

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 CCl 4 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.