The reactivity of N-heterocyclic carbenes and their precursors with [Ru-3(CO)(12)]

The ambient temperature reaction of the N-heterocyclic carbenes (NHCs) 1,3-dimesitylimidazol-2- ylidene (IMes) and 1,3-bis(2,6-diisopropylphenyl) imidazol-2-ylidene (IDipp) with the triruthenium cluster [Ru-3(CO)(12)], in a 3:1 stoichiometric ratio, results in homolytic cleavage of the cluster to quantitatively afford the complexes [Ru(CO)(4)(NHC)] (1; NHC = IMes, 2; NHC = IDipp). Reaction of the 2-thione or hydrochloride precursors to IMes, i.e. S=IMes and IMes.HCl, with the same triruthenium cluster affords the complexes [Ru-4(mu(4)-S)(2)(CO)(9)(IMes)(2)] (3) and [Ru-4(mu(4)-S)(CO)(10)(IMes)(2)] (4) (3 : 1 and 2 : 1 reaction), and [{Ru(mu-Cl)(CO)(2)(IMes)}(2)] (7) (3 : 1 reaction) respectively. By contrast, the complex [Ru-3(mu(3)-S)(2)(CO)(7)(IMeMe)(2)] (6), where IMeMe is 1,3,4,5-tetramethylimidazol-2-ylidene, is the sole product of the 2 : 1 stoichiometric reaction of S=IMeMe with [Ru-3(CO)(12)]. Compounds 1-4, 6 and 7 have been structurally characterised by single crystal X-ray diffraction.