Synthesis and Application of Stereoretentive Ruthenium Catalysts on the Basis of the M7 and the Ru–Benzylidene–Oxazinone Design

Preserving precise choreography of bonds in Z-stereoretentive olefin metathesis by using quinoxaline-2,3-dithiolate ligand

The Z-alkene geometry is prevalent in various chemical compounds, including numerous building blocks, fine chemicals, and natural products. Unfortunately, established Mo, W, and Ru Z-selective catalysts lose their selectivity at high temperatures required for industrial processes like reactive distillation, which limits their synthetic applications. To address this issue, we develop a catalyst capable of providing Z-alkenes with high selectivity under harsh conditions. Our research reveals a dithiolate ligand that, stabilised by resonance, delivers high selectivity at temperatures up to 150 °C in concentrated mixtures. This distinguishes the dithioquinoxaline complex from existing Z-selective catalysts. Notably, this trait does not compromise the new catalyst's usability under classical conditions, matching the activity of known stereoretentive catalysts. Density Functional Theory calculations were employed to understand the reaction mechanism and selectivity, and to investigate the poisoning that the catalyst may undergo and how it competes with catalytic activity. Furthermore, the quinoxaline-based catalyst enables the valorisation of bio-sourced alkene feedstocks and the production of agricultural sex pheromones for pest control.

A tunable family of CAAC-ruthenium olefin metathesis catalysts modularly derived from a large-scale produced ibuprofen intermediate

A series of tunable CAAC-based ruthenium benzylidene complexes with increased lipophilicity derived from a ketone being a large-scale produced key substrate for a popular nonsteroidal anti-inflammatory drug-ibuprofen was obtained and tested in various olefin metathesis transformations. As a group, these catalysts exhibited higher activity than their known analogues containing a smaller and less lipophilic phenyl substituent on the α-carbon atom, but in individual reactions, the size of the N-aryl moiety was revealed as a decisive factor. For example, in the cross-metathesis of methyl oleate with ethylene (ethenolysis)-a reaction with growing industrial potential-the best results were obtained when the N-aryl contained an isopropyl or tert-butyl substituent in the ortho position. At the same time, in the RCM, CM, and self-CM transformations involving larger olefinic substrates, the catalysts with smaller aryl-bearing CAAC ligands, where methyl and ethyl groups occupy ortho, ortho' positions performed better. This offers a great deal of tunability and allows for selection of the best catalyst for a given reaction while keeping the general structure (and manufacturing method) of the ibuprofen-intermediate derived CAAC ligand the same.

Unexpected Latency of Z-Stereoretentive Ruthenium Olefin Metathesis Catalysts Bearing Unsymmetrical N-heterocyclic Carbene or Cyclic(alkyl)(amino)carbene Ligands

A set of ruthenium complexes bearing a CAAC or uNHC ligand and a dithiocatechol fragment have been obtained and characterized spectroscopically. The activity and Z-selectivity of the newly obtained catalysts were studied in selected model CM, self-CM, and RCM olefin metathesis reactions. Intriguingly, and in contrast to structurally related NHC-bearing catalysts Ru4a and Ru4b, the CAAC and uNHC analogues showed no or only very little activity in olefin metathesis. Interestingly, despite being not productive in metathesis reactions conducted in solution, Ru8 enabled the synthesis of a model 16-membered macrocyclic lactone of valuable musk smell with excellent chemoselectivity (no C-C double-bond migration was observed) at a concentration 40 times higher than that typically used by organic chemists in similar macrocyclizations (200 mM instead of 5 mM) with excellent Z-selectivity. Unfortunately, also here the conversion was low.

A tutorial review of stereoretentive olefin metathesis based on ruthenium dithiolate catalysts

Stereoretentive olefin metathesis based on ruthenium dithiolate complexes has become a very active field of research within the past years. This unique catalyst class is able to kinetically produce both Z- and E-alkenes in high stereochemical purity (typically >95:5) starting from stereochemically pure Z- or E-alkenes. The aim of this tutorial review is to organize the reported information concerning ruthenium dithiolate catalysts in a logic manner, thus providing an "operators handbook" for chemists who wish to apply this methodology in synthesis.