A fast-initiating ionically tagged ruthenium complex: A robust supported pre-catalyst for batch-process and continuous-flow olefin metathesis

In this study, a new pyridinium-tagged Ru complex was designed and anchored onto sulfonated silica, thereby forming a robust and highly active supported olefin-metathesis pre-catalyst for applications under batch and continuous-flow conditions. The involvement of an oxazine-benzylidene ligand allowed the reactivity of the formed Ru pre-catalyst to be efficiently controlled through both steric and electronic activation. The oxazine scaffold facilitated the introduction of the pyridinium tag, thereby affording the corresponding cationic pre-catalyst in good yield. Excellent activities in ring-closing (RCM), cross (CM), and enyne metathesis were observed with only 0.5mol % loading of the pre-catalyst. When this powerful pre-catalyst was immobilized onto a silica-based cationic-exchange resin, a versatile catalytically active material for batch reactions was generated that also served as fixed-bed material for flow reactors. This system could be reused at 1mol % loading to afford metathesis products in high purity with very low ruthenium contamination under batch conditions (below 5ppm). Scavenging procedures for both batch and flow processes were conducted, which led to a lowering of the ruthenium content to as little as one tenth of the original values. Tag! You're it! A pyridinium-tagged Ru complex (see figure) that was anchored to sulfonated silica formed a robust and highly active supported olefin-metathesis pre-catalyst for applications under batch and continuous-flow conditions with low ruthenium leaching.