Development of Aqueous Metathesis Catalysts

Recent developments (and some historical aspects) of protic solvent metathesis using ill-defined catalysts [e. g., RuCl3 center dot H2O and Ru(H2O)(6)(tos)(2)] and also the more easily handled, well-defined ruthenium-based alkylidene complexes (based on 15, 16, and 17) are highlighted. Modification of these catalysts has been achieved for applications in protic solvents with the introduction of water-solubilizing ligands and by immobilization onto a suitable support. The introduction of water-solubilizing cationic and anionic phosphines is synthetically straightforward with various catalysts having been prepared in this way (see 18, 19, 29-32, 36). Immobilzation methods include tethering to a water-soluble polymeric support (see 39, 40) and modification of the benzylidene group (see 43-46). Ionic tags have also been attached to the benzylidene group (see 48-50, 52, 53). Several other approaches have also been reported as discussed here to prepare modified catalysts that display good activity in protic media (see 54-59).