Chemodivergent metathesis of dienynes catalyzed by ruthenium-indenylidene complexes: An experimental and computational study

A study on the enyne meta-thesis reaction leading to the formation cyclic compounds using ruthenium-in-denylidene complexes is presented. Several l, 11-dien-6-ynes have been subjected to ruthenium metathesis cyc-lization by using ruthenium-indenyli-dene complexes bearing various phos-phine and N-heterocyclic carbene (NHC) ligands. Interestingly, for some substrates chemodivergent metathesis occurs and is a function of the catalyst employed. This led us to investigate the competing "ene-then-yne" or "yne-then-ene" reaction pathways apparent-ly at play in these systems using both experimental observations and DFT calculations. Experimental and compu-tational studies were found in good agreement and permit to conclude that for phosphine-containing catalysts, the "ene-then-yne" pathway is exclusively adopted. On the other hand, for cata-lysts bearing NHC ligands, both path-ways are possible.