Silica Immobilized Hoveyda Type Pre-Catalysts: Convenient and Reusable Heterogeneous Catalysts for Batch and Flow Olefin Metathesis

Abstract

Two Hoveyda type ruthenium metathesis precatalysts, Umicore M51 and Umicore M71 SIMES, were immobilized on commercial silica in a simple and fast procedure through direct interaction with the support surface. These precatalysts exhibited good activity in ring-closing, cross, and enyne metathesis reactions and were stable in terms of reusability to be used for consecutive runs under both batch and flow conditions. In non-polar media, the catalytic activity of the precatalysts is truly based on a heterogeneous species, and the contamination of the products with ruthenium was very low with respect to starting catalyst (0.003–0.01 %; 0.13–0.44 ppm). If necessary, such as in solvents like toluene, the ruthenium content can easily be reduced to levels below 0.5 ppm by treatment of the crude metathesis products with the commercial scavenger QuadraSil AP or by use of an additional QuadraSil AP scavenger cartridge under flow conditions.