The reactivity of N-heterocyclic carbenes and their precursors with [Ru3(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 [Ru3(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[double bond, length as m-dash]IMes and IMes·HCl, with the same triruthenium cluster affords the complexes [Ru4(μ4-S)2(CO)9(IMes)2] (3) and [Ru4(μ4-S)(CO)10(IMes)2] (4) (3 : 1 and 2 : 1 reaction), and [{Ru(μ-Cl)(CO)2(IMes)}2] (7) (3 : 1 reaction) respectively. By contrast, the complex [Ru3(μ3-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[double bond, length as m-dash]IMeMe with [Ru3(CO)12]. Compounds 1–4, 6 and 7 have been structurally characterised by single crystal X-ray diffraction.