Chemodivergent Metathesis of Dienynes Catalyzed by Ruthenium-Indenylidene Complexes: An Experimental and Computational Study

A study on the enyne metathesis reaction leading to the formation cyclic compounds using ruthenium-indenylidene complexes is presented. Several 1,11-dien-6-ynes have been subjected to ruthenium metathesis cyclization by using ruthenium-indenylidene complexes hearing various phosphine 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 "enc-then-yne" of "yne-then-ene" reaction pathways apparently at play in these systems using both experimental observations and DFT calculations. Experimental and computational 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. fur catalysts bearing NHC ligands, both pathways are possible.