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 (Ph2PC6H4CH2ImMe) and 1-[{2-(dicyclohexylphosphino)­phenyl}­methyl]-3-methylimidazol-2-ylidene
(Cy2PC6H4CH2ImMe) and
the NHC-functionalized
thioether 1-{(2-methylsulfide)­ethyl}-3-methylimidazol-2-ylidene
(MeSCH2CH2ImMe) with [Ru3(CO)12] have been studied. Both NHC-phosphines react with equimolar
amounts of [Ru3(CO)12], in
THF at room temperature, to give the edge-bridged disubstituted products
[Ru3(μ-κ2P,CNHC-R2PC6H4CH2ImMe)­(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 [Ru3(μ-H)2(μ3-κ3P,C,CNHC-R2PC6H4CImMe)­(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
[Ru3(CO)12] with 3 equivalents of Ph2PC6H4CH2ImMe leads to the mononuclear
ruthenium(0) complex [Ru­(κ2P,CNHC-Ph2PC6H4CH2ImMe)­(CO)3] (5). No trinuclear derivatives
were obtained from reactions of [Ru3(CO)12]
with MeSCH2CH2ImMe, the tetranuclear derivative [Ru4(μ-κ2S,CNHC-MeSCH2CH2ImMe)­(μ-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.