Q: If ruthenium-based olefin metathesis catalysts are tolerant of water, then can you run a metathesis reaction in water as a solvent?
A: It depends.
It’s true that the Grubbs-type catalyst systems aren’t particularly reactive with water. When it comes to running ruthenium-based metathesis reactions in water, the biggest problem is solubility. Due to environmental concerns, there’s been a recent emphasis on replacing organic solvents with water, and a number of practical processes have been developed to run organic reactions in or “on water.”
The debate will undoubtedly continue as to whether water is an environmentally-friendly solvent (decontamination of aqueous waste is a costly problem, after all). But for the cases where you want to (for environmental reasons) or need to (for substrate solubility reasons) run a metathesis reaction in water, this review by Burtscher and Grela is a great resource. It highlights the various strategies employed to run olefin metathesis reactions using water as a solvent.
Topics include the use of cosolvents, emulsions and surfactants for water-insoluble catalysts, and the design and use of water-soluble catalysts and precatalysts.