Facile Anionic Ligand Exchange in S-chelated Ruthenium Complexes, What is the Impact On the Course of the Metathesis Reaction?

Extensive development of ruthenium complexes for olefin metathesis has enabled fine tuning of many aspects of the reaction. Two highly important properties are asymmetric metathesis by chiral ruthenium pre-catalysts and latent olefin metathesis that may be provided by S-chelated ruthenium complexes. We have developed an innovative and highly facile protocol for the synthesis of benzylidene type ruthenium pre-catalysts, bearing amino acids as chiral anionic ligands, and established their application in asymmetric ring closing metathesis. At the same time, careful design of the cis-dichloro S-chelated ruthenium scaffold led to increased stability and reactivity after activation, as well as better accommodation of highly demanding tetra-substituted olefins. As both projects emphasized the importance of the dynamic nature of the anionic ligands; exploration of the nature of these ligands in different ruthenium frameworks will provide vital information for the syntheses of efficient and economical new catalysts for a variety of olefin metathesis reactions.