Regarding the mechanism of olefin metathesis with sol-gel-supported ru-based complexes bearing a bidentate carbene ligand. Spectroscopic evidence for return of the propagating Ru carbene

Two isotopically and structurally labeled Ru-based carbenes (2-d(4) and 13) have been prepared and attached to the surface of monolithic sol-gel glass. The resulting glass-supported complexes (18-d(n) and 19) exhibit significant catalytic activity in promoting olefin metathesis reactions and provide products of high purity. Through analysis of the derivatized glass pellets used in a sequence of catalytic ring-closing metathesis reactions mediated by various supported Ru carbenes, it is demonstrated that free Ru carbene intermediates in solution can be scavenged by support-bound styrene ether ligands prior to the onset of competing transition metal decomposition. The observations detailed herein provide rigorous evidence that the initially proposed release/return mechanism is, at least partially, operative. The present investigations shed light on a critical aspect of the mechanism of an important class of Ru-based metathesis complexes (those bearing a bidentate styrene ether ligand).