The Impact of Water on Ru-Catalyzed Olefin Metathesis: Potent Deactivating Effects Even at Low Water Concentrations
Résumé
Ruthenium catalysts for olefin metathesis are widely viewed as water-tolerant. Evidence is presented, however, that even low concentrations of water cause catalyst decomposition, severely degrading yields. Of 11 catalysts studied, fast-initiating examples (e.g., the Grela catalyst RuCl2(H2IMes)(=CHC6H4-2-O i Pr-5-NO2) were most affected. Highest water-tolerance was exhibited by slowly-initiating iodide and cyclic (alkyl)(amino)carbene derivatives. Computational investigations indicated that hydrogen-bonding of water to substrate can also play a role, by retarding cyclization relative to decomposition. These results have important implications for olefin metathesis in organic media, where water is a ubiquitous contaminant, and for aqueous metathesis, which currently requires superstoichiometric "catalyst" for demanding reactions.
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