Olefin metathesis in confined spaces: the encapsulation of Hoveyda-Grubbs catalyst in peanut, square, and capsule shaped hollow silica gels

In this study, Hoveyda-Grubbs 2nd generation (HG2) catalyst was encapsulated in hollow mesoporous silica gels with various morphologies (peanut, square, and capsule) by reducing the pore size of the mesoporous shell. The resulting catalytic system efficiently catalyzed the ring-closing metathesis of diethyl diallylmalonate, as well as the ethenolysis reactions of methyl oleate and fatty acid methyl ester mixtures. The interior void in hollow silica gel provided a confined isolated site for both ruthenium catalyst and olefinic substrates where the performance and recyclability in metathesis reactions were improved compared to the homogenous analogs. Finally, the catalyst could be easily recycled and used in ring-closing metathesis of diethyl diallylmalonate up to the 10th turn. In sum, this study has demonstrated that hollow silica gels are efficient materials for the encapsulation of homogenous catalysts, which improve the stability of the HG2 even under an air atmosphere, maintaining its activity for up to 6 months of storage time on the benchtop.