Encapsulation of an Olefin Metathesis Catalyst in the Nanocages of SBA-1: Facile Preparation, High Encapsulation Efficiency, and High Activity

By postreducing the window size through silylation, 2nd generation Hoveyda-Grubbs catalyst was encapsulated in the nanocages of a mesoporous material SBA-1. The encapsulation efficiency of SBA-1 was up to 70%, much higher than that of other mesoporous materials such as SBA-16, FDU-12, and MCM-41 (0-43 %). The successful encapsulation was confirmed by N-2 sorption analysis and FTIR and diffusion reflectance UV/Vis spectroscopy. Such a SBA-1-encapsulated catalyst showed good activity in both olefin ring-closing metathesis and cross metathesis. A wide range of olefins could be transformed to the desired products with conversions of 27-100 %. The encapsulated catalyst showed more sensitive temperature effects than the homogeneous counterpart, reflecting the unique properties of the encapsulated catalyst. At reaction temperatures of 40-60 degrees C, the activity of the encapsulated catalyst was sufficiently comparable to that of the homogeneous catalyst for the cross metathesis of styrene-type substrates, probably because of the confinement effects of the nanocages. The solid catalyst could be recycled seven times. This study not only supplies a new solid catalyst for olefin metathesis but also demonstrates our improvement in immobilizing metal complex catalyst toward a green and effective level.