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

Abstract

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.

Ruthenium Olefin Metathesis Catalysts with Six-Membered Chelating Dithioacetal Ligands: Synthesis and Reactivity

“…Thus, introducing aromatic substituents to the six-membered Ru–S chelates makes them lose their latency. Notably, this behavior was not observed in the Zubkov catalysts, where all cis -dichloro complexes were reported to be fully latent at ambient conditions . One of the reasons for this very significant and unexpected change in activity could be a lowering of the isomerization activation energy, and we are currently investigating the reasons for this behavior.…”

“…54 Much more recently, Zubkov and co-workers synthesized and fully characterized a series of seven new six-membered S-chelated complexes (both in their cis-dichloro and trans-dichloro configurations) and reported their RCM and ROMP activity. 55 Seeing the potential of this type of complexes and given our expertise in the area, we set out to investigate the synthesis and development of these understudied Ru complexes by utilizing a dithioacetal moiety and to further understand the effects of their potential thermal/photochemical activity. To begin our studies, we prepared and fully characterized four Ru−S sixmembered ring chelated catalysts (Scheme 1, Figure 2).…”

“…In 2016, Shcheglova and co-workers reported six-membered S-chelated complexes that boasted trans -dichloro geometry and showed poor activity for RCM at room temperature . Much more recently, Zubkov and co-workers synthesized and fully characterized a series of seven new six-membered S-chelated complexes (both in their cis -dichloro and trans -dichloro configurations) and reported their RCM and ROMP activity . Seeing the potential of this type of complexes and given our expertise in the area, we set out to investigate the synthesis and development of these understudied Ru complexes by utilizing a dithioacetal moiety and to further understand the effects of their potential thermal/photochemical activity.…”

Reactivity regulation for olefin metathesis-catalyzing ruthenium complexes with sulfur atoms at the terminal of 2-alkoxybenzylidene ligands

“…The structural modification of the phenolic moiety is useful for controlling the reactivity of Fig. 1 Hoveyda-Grubbs 2nd generation catalyst (HG-II, 1) and its derivatives with thioether substitution at the phenolic oxygen; (a) structures of HG-II and its derivatives; [21][22][23][24][25][26][27][28][29] (b) cis/trans ligand isomerization by photo-irradiation or heating. 22,23…”

“…The cis / trans coordination mode also depends on the steric hindrance around the metal center. For example, complexes 5a , 27 5b , 27 and 5c 28 have a methylene linker between the sulfur atom and the phenyl part, resulting in a six-membered trans -dichlorido configuration as a thermodynamically favorable form despite S -chelation. 27,28 In contrast, ruthenium complexes with dithioacetal benzylidene ligands (complexes 6a–6d 29 ) exhibit a six-membered cis -dichlorido configuration although these complexes have a methylene linker similar to complexes 5a–5c .…”