Stability and activity of cis-dichloro ruthenium olefin metathesis precatalysts bearing chelating sulfur alkylidenes

S -Chelated Grubbs type complexes are usually found in their stable cis -dichloro conformation. These precatalysts are usually latent and necessitate external stimuli to promote olefin metathesis reactions. Herein we report the synthesis of new S -chelated ruthenium complexes, by a simple exchange of the benzylidene to an alkylidene chelating ligand. The structure of the complexes was studied by NMR spectroscopy, single crystal X-ray diffraction and DFT calculations. The new complexes were tested in a series of olefin metathesis reactions and were found to be the first cis -dichloro ruthenium precatalysts that are active at room temperature. The observed differences in reactivity and structure between the alkylidene complexes and their benzylidene counterparts highlight the important influence aromaticity may have on the stability and activity of chelated Grubbs type complexes. The findings may also have implications to develop alternative strategies to stabilize, or destabilize, other organometallic complexes bearing relevant chelating ligands.