Water-Accelerated Decomposition of Olefin Metathesis Catalysts

Water is ubiquitous in olefin metathesis, at levels ranging from contaminant to cosolvent. It is also non-benign. Water-promoted catalyst decomposition competes with metathesis, even for robust ruthenium catalysts. Metathesis is hence typically noncatalytic for demanding reactions in water-rich environments (e.g., chemical biology), a challenge as the Ru decomposition products promote unwanted reactions such as DNA degradation. To date, only the first step of the decomposition cascade is understood: catalyst aquation. Here we demonstrate that the aqua species dramatically accelerate both beta-elimination of the metallacyclobutane intermediate and bimolecular decomposition of four-coordinate [RuCl-(H2(O))(n)(L)(=CHR)]Cl. Decomposition can be inhibited by blocking aquation and beta-elimination.

Automated summary

Water has a significant impact on olefin metathesis, as it can react with catalysts and cause decomposition of the reaction intermediates. This poses a challenge for demanding reactions in water-rich environments, as metathesis is typically noncatalytic under these conditions.