Properties and Catalytic Activity of Hoveyda–Grubbs-Type Catalysts with an S → Ru Coordination Bond in a Six-Membered Chelate Ring

This work continues our group’s research into the synthesis and study of the catalytic activity of ruthenium chelates with various heteroatoms (O, S, N, and Se) in a six-membered ring. It was found that second-generation Hoveyda–Grubbs-type catalysts containing a sulfur-ruthenium coordinate bond in a six-membered chelate ring can be prepared easily and in high yields using standard procedures, based on the interaction between (2-vinylbenzyl)sulfanes and Ind II (the common precursor for Ru-complex synthesis). The obtained ruthenium derivatives, with a donor-acceptor S → Ru bond, can exist in two isomeric forms according to the arrangement of substituents around the central metal atom. Kinetically controlled trans-isomers are formed at temperatures below 80 °C in heptane and are less thermodynamically stable compared with cis-isomers, which arise under heating of trans-S-chelates in 1,2-dichloroethane at 110 °C. The structures of all the cis- and trans-isomers were determined and characterized in detail by X-ray diffraction and nuclear magnetic resonance. The study of the activity of the catalysts in standard ring-closing metathesis and ring-opening metathesis polymerization reactions showed that the cis-isomers are inactive in the absence of thermal or UV activation, while trans-complexes of the same type display excellent catalytic properties at r.t. that are superior to those of the commercially available HG-II catalyst. The structure, spectral characteristics, and catalytic activity of the catalysts containing an S → Ru bond in a six-membered chelate ring were compared with their five-membered analogues obtained in previous works.