Grubbs' Catalyst - Hoveyda-Grubbs Catalyst

In the Hoveyda-Grubbs Catalyst the benzylidene ligand has a chelating isopropxy group attached to the benzene ring. The chelating oxygen atom replaces a phosphine ligand, which for the 2nd generation catalyst gives a completely phosphine-free structure. The Hoveyda-Grubbs catalysts, while more expensive and slower to initiate than the Grubbs catalyst from which they are derived, are popular because of their improved stability. Hoveyda-Grubbs catalysts are easily formed from the corresponding Grubbs catalyst by the addition of the chelating ligand and the use of a phosphine scavenger like copper(I) chloride:

The 2nd generation Hoveyda-Grubbs catalysts can also be prepared from the 1st generation Hovedya-Grubbs catalyst by the addition of the NHC:

In one study a water soluble Grubbs catalyst is prepared by attaching a polyethylene glycol chain to the imidazolidine group. This catalyst is used in the ring-closing metathesis reaction in water of a diene carrying an ammonium salt group making it water-soluble as well.