Hydroxide-Induced Degradation of Olefin Metathesis Catalysts: A Challenge for Metathesis in Alkaline Media

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.

本研究以霍维达催化剂HII（Hoveyda catalyst HII）为研究对象，证实氢氧根离子可有效破坏钌（Ru）催化的烯烃复分解反应。向反应体系中加入四丁基氢氧化铵（[NnBu4][OH]）后，HII催化的复分解反应会立即终止，该效应源于双（氢氧根）配合物HII–OH（bis(hydroxide) complex HII–OH）的生成。该配合物已被合成以用于直接研究。HII–OH与烯烃的引发反应速率极为缓慢，且会在复分解反应的首个循环中发生分解。计算分析结果显示，HII–OH与其四配位亚甲基衍生物之间可发生快速双分子偶联。值得关注的是，完全分解的催化剂还会加速HII–OH的降解过程。研究人员提出，氢氧根配体的氢键结合能力是该降解过程的强效驱动力。