The Activation Mechanism of Ru–Indenylidene Complexes in Olefin Metathesis

Olefin metathesis is a powerful tool
for the formation of carbon–carbon
double bonds. Several families of well-defined ruthenium (Ru) catalysts
have been developed during the past 20 years; however, the reaction
mechanism for all such complexes was assumed to be the same. In the
present study, the initiation mechanism of Ru–indenylidene
complexes was examined and compared with that of benzylidene counterparts.
It was discovered that not all indenylidene complexes followed the
same mechanism, highlighting the importance of steric and electronic
properties of so-called spectator ligands, and that there is no single
mechanism for the Ru-based olefin metathesis reaction. The experimental
findings are supported quantitatively by DFT calculations.