Hydroxide-Induced Degradation of Olefin Metathesis Catalysts: A Challenge for Metathesis in Alkaline Media
Résumé
Hydroxide ion is shown to be a potent disruptor of Ru-catalyzed olefin metathesis, in a study of the Hoveyda catalyst HII. Addition of [NnBu4][OH] immediately terminates metathesis via HII, an effect traced to formation of bis(hydroxide) complex HII–OH. The latter was synthesized for direct study. HII–OH initiates very slowly on reaction with olefins, and decomposes in the first cycle of metathesis. Computational analysis reveals rapid bimolecular coupling between HII–OH and its four-coordinate methylidene derivative. Importantly, fully decomposed catalyst also accelerates decomposition of HII–OH. The H-bonding capacity of the hydroxide ligand is proposed as a powerful driving force for degradation.
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