Effect of Added Salt on Ring-Closing Metathesis Catalyzed by a Water-Soluble Hoveyda–Grubbs Type Complex To Form N‑Containing Heterocycles in Aqueous Media

The efficiency of ring-closing metathesis catalyzed by a Hoveyda–Grubbs type catalyst in water can be enhanced by addition of a chloride salt under neutral conditions. UV–vis spectroscopic study showed that a characteristic band of the catalyst around 380 nm remained over 16 h in the presence of KCl, whereas the band distinctly decreased in the absence of KCl. The disappearance of the band is ascribed to a displacement of a chloride ligand by a water molecule or a hydroxide anion. The spectral changes can be related to the metathesis activity. The experimental results indicate that avoidance of the chloride ligand loss is important to maintain the metathesis activity in water.