Reactivity of phosphine- and thioether-tethered N-heterocyclic carbenes with ruthenium carbonyl

The reactions of the NHC-functionalized phosphines 1-[{2-(diphenylphosphino)phenyl}methyl]-3-methylimidazol-2-ylidene (Ph(2)PC(6)H(4)CH(2)ImMe) and 1-[{2-(dicyclohexylphosphino)phenyl}methyl}-3-methylimidazol-2-ylidene (Cy(2)PC(6)H(4)CH(2)ImMe) and the NHC-functionalized thioether 1-{(2-methylsulfide)ethyl}-3-methylimidazol-2-ylidene (MeSCH(2)CH(2)ImMe) with [Ru-3(CO)(12)] have been studied. Both NHC-phosphines react with equimolar amounts of [Ru-3(CO)(12)], in THF at room temperature, to give the edge-bridged disubstituted products [Ru-3(mu-kappa P-2,C-NHC-R(2)PC(6)H(4)CH(2)ImMe)(CO)(10)}, R = Ph (1), Cy (2), which selectively undergo a double C-H bond activation of their CH2 group upon gentle warming (R = Ph) or at room temperature (R = Cy) to give the dihydrido derivatives [Ru-3(mu-H)(2)(mu(3)-kappa P-3,C,C-NHC-R(2)PC(6)H(4)CImMe)(CO)(8)}, R = Ph (3) and Cy (4), respectively. These products contain novel face-capping ligands that arise from the oxidative addition of both C H bonds of the corresponding NHC-phosphine ligand CH2 group. This double-metalation process is facilitated by the rigidity of the C6H4CH2 linker of these ligands. The treatment of [Ru-3(CO)(12)] with 3 equivalents of Ph(2)PC(6)H(4)CH(2)ImMe leads to the mononuclear ruthenium(0) complex [Ru(kappa P-2,C(NHC)Ph(2)PC(6)H(4)CH(2)ImMe)(CO)(3)} (5). No trinuclear derivatives were obtained from reactions of [Ru-3(CO)(12)] with MeSCH(2)CH(2)ImMe, the tetranuclear derivative [Ru-4(mu-kappa S-2,C-NHC-MeSCH(2)CH(2)ImMe)(mu-CO)(2)(CO)(10)) (6) being the only product that could be isolated. Compound 6 contains a butterfly arrangement of the metal atoms with the wing tips bridged by the ligand sulfur atom, while the NHC fragment is attached to one wing tip.