Ammonium tagged Hoveyda-Grubbs catalyst immobilized on yolk/shell silica gels with a hydrophobic shell for olefin metathesis reactions

In this study, we have developed a novel yolk-shell silica material with a hydrophobic shell and a void interphase to encapsulate quaternary ammonium-tagged Hoveyda-Grubbs catalysts (Aquamet) for efficient ring-closing metathesis and ethenolysis reactions. This design facilitates the efficient diffusion of olefinic substrates into the catalyst core while simultaneously stabilizing ethylene gas within the hollow structure during the ethenolysis reactions. The hydrophobic characteristics of the outer layer improve the diffusion of hydrophobic substrates and serve as a moisture barrier, enhancing catalyst stability. The catalytic system has reached a turn-over number of 1000 for ethenolysis of methyl oleate at atmospheric pressure, yielding the corresponding ethenolysis products with 99% selectivity. The catalyst demonstrated excellent reusability, maintaining high efficiency up to the 8^th cycle in ring-closing metathesis reactions of diethyl diallymalonate with minimal catalyst loss of only 0.5 mol%.