Water-soluble ruthenium alkylidenes: Synthesis, characterization, and application to olefin metathesis in protic solvents

Ruthenium alkylidenes 6 and 7 bearing cationically functionalized phosphine ligands are soluble and stable in protic solvents and initiate olefin meta thesis reactions in methanol, water, and aqueous emulsions. NMR spectroscop y data and X-ray diffraction analyses of alkylidene 6 suggested that these new alkylidenes were structurally similar to previously reported complexes of the type (PR3)(2)Cl2Ru=CHR, in which the alkylidene substituents lie in the CI-Ru-Cl plane. The anionic chloride ligands of complexes 6 and 7 were found to undergo facile Ligand exchange reactions with other anions in prot ic solution. Both alkylidenes initiate the ring-opening metathesis polymeri zation (ROMP) of strained, cyclic olefins in water. However, the propagatin g species in these reactions decompose prior to complete consumption of mon omer. These complexes initiate the quantitative, living polymerization of f unctionalized monomers in water in the presence of a Bronsted acid. Both ch ain termination and chain transfer reactions were experimentally demonstrat ed to be absent on the time scale of these acid-activated polymerizations. Alkylidenes 6 and 7 react readily with acyclic olefins: alkylidene 6 reacte d with trans-2-butene to yield a new ethylidene complex in either methanol or water, and the treatment of 6 with tri(ethylene glycol) methyl vinyl eth er in water yielded water-soluble Fischer-carbene complex 16.