Ru-Based Complexes with Quaternary Ammonium Tags Immobilized on Mesoporous Silica as Olefin Metathesis Catalysts

Abstract

Ruthenium olefin metathesis catalysts bearing a polar quaternary ammonium group in N-heterocyclic ligand were immobilized on silica and siliceous mesoporous molecular sieves with different pore sizes (SBA-15 and MCM-41). The activity of the heterogeneous catalysts was found to increase with an increase in pore size of the support used, with the best results observed for SBA-15-supported catalyst. The influence of reaction conditions (temperature, solvent, catalyst, and substrate concentration) on the efficiency of new heterogeneous catalysts was established. A significant influence of the counterion present in the ruthenium complex on the activity of immobilized catalysts was also found: those derived from chloride containing ion exhibited the highest activity. High activity in ring-closing metathesis of substrates as citronellene, 1,7-octadiene, and diallyl compounds as well as in cross-metathesis of unsaturated aliphatic compounds with methyl acrylate was observed under optimized conditions. In some cases, heterogenization led to catalysts with efficiency higher than those observed for corresponding homogeneous complexes