Olefin Metathesis Transformations Research Articles

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.

Pushing the Bounds of Olefin Metathesis with Vanadium

AbstractOlefin metathesis has been a key player in organic and polymer synthesis for over 50 years. While countless catalysts have been reported over this time, new compounds that offer improved selectivity, efficiency, robustness, and/or cost‐effectiveness are still highly desired. This minireview will detail efforts made in this regard through the development of catalysts based on abundant and inexpensive vanadium. Special attention will be given to reports within the past three years concerning ring‐opening metathesis polymerization of low ring‐strain cyclic olefins and expansion to other olefin metathesis transformations, such as cross‐metathesis.

Ammonium-tagged ruthenium-based catalysts for olefin metathesis in aqueous media under ultrasound and microwave irradiation.

The influence of microwave and ultrasonic irradiation on the performance of ammonium-tagged Ru-based catalysts in olefin metathesis transformations in aqueous media was studied. Differences in the catalytic activity in correlation with the nature of the present counter ion and the size of the N-heterocyclic carbene (NHC) ligand were revealed. The presented methodology allows for preparation of a variety of polar and non-polar metathesis products under environmentally friendly conditions.

Ammonium NHC-tagged olefin metathesis catalysts – influence of counter-ions on catalytic activity

Ruthenium-based catalysts bearing quaternary ammonium groups in their N-heterocyclic carbene (NHC) fragments and different counter-ions were synthesised and tested in various olefin metathesis transformations.

Multiple Olefin Metathesis Polymerization That Combines All Three Olefin Metathesis Transformations: Ring-Opening, Ring-Closing, and Cross Metathesis.

We demonstrated tandem ring-opening/ring-closing metathesis (RO/RCM) polymerization of monomers containing two cyclopentene moieties and postmodification via insertion polymerization. In this system, well-defined polymers were efficiently formed by tandem cascade RO/RCM reaction pathway. Furthermore, these polymers could be transformed to new A,B-alternating copolymers via a sequential cross metathesis reaction with a diacrylate. Additionally, we demonstrated the concept of multiple olefin metathesis polymerization in which the dicyclopentene and diacrylate monomers underwent all three olefin metathesis transformations (ring-opening, ring-closing, and cross metathesis) in one shot to produce A,B-alternating copolymer.

ChemInform Abstract: Synthesis Optimization and Catalytic Activity Screening of Industrially Relevant Ruthenium‐Based Metathesis Catalysts

AbstractReview: 58 refs.

Olefin metathesis transformations in thermomorphic multicomponent solvent systems

Homogeneous catalysis is a major actor of modern chemistry with a growing impact on clean and sustainable chemical processes. However, for many industrial applications of homogeneously catalyzed reactions, an easy separation and recovery of the catalyst should be guaranteed. Temperature-dependent multicomponent solvent (TMS) systems have been evaluated in ruthenium catalyzed olefin metathesis transformations. Propylene carbonate was found a suitable solvent for the ruthenium catalyzed ring-closing and cross-metathesis transformations of a variety of substrates including renewable fatty esters. The potential of a TMS system consisting of propylene carbonate/ethyl acetate/cyclohexane was then evaluated in the cross-metathesis of the renewable methyl 10-undecenoate with methyl acrylate and acrylonitrile.

Synthesis Optimization and Catalytic Activity Screening of Industrially Relevant Ruthenium-Based Metathesis Catalysts

Olefin metathesis is a powerful catalytic reaction that has a huge potential in the pharmaceutical, polymer and specialty chemicals industries. Cost-effective industrial applications require large-scale availability of catalyst precursors which combine high activity, high selectivity and long life-time. Among the known numerous families of olefin metathesis catalysts, the Umicore M7-catalyst family represents a novel class of Hoveyda-type complexes showing excellent chemical stabilities and modular activity profiles. Relevant aspects related to their industrial synthesis as well as their catalytic performance in valuable olefin metathesis transformations are overviewed here.

Ruthenium Olefin Metathesis Catalysts with Frozen NHC Ligand Conformations

The catalytic behavior of Grubbs and Hoveyda–Grubbs II type ruthenium complexes bearing N-heterocyclic carbene (NHC) ligands with syn-phenyl groups on the backbone and syn- or anti-oriented o-tolyl N-substituents was evaluated in a series of olefin metathesis transformations. Further advance in the synthesis of the best-performing syn catalysts and a deeper investigation into the solution-state structure of the Hoveyda–Grubbs type II complex with anti N-tolyl groups by 2D-NMR and DFT studies are also reported. Of particular interest, syn complexes emerged among the best-performing catalysts in all of the explored metathesis reactions, especially in the ring-closing metathesis (RCM) of hindered olefins, allowing also for the difficult formation of macrocyclic trisubstituted alkenes. An important unexpected result was obtained in the RCM of linalool, where both syn and anti catalysts appeared to be involved in the dehydration reaction of the cyclization product (1-methylcylopent-2-en-1-ol). This process all...

Screening of a selection of commercially available homogeneous Ru-catalysts in valuable olefin metathesis transformations

A library of thirteen different commercially available Ru-based catalysts was evaluated in valuable metathesis reactions for the production of fragrance and bioactive molecule precursors. Rigorous library screening clearly illustrated the different catalytic behaviour of the catalyst selection and highlighted its significant advantage to provide efficiency in specific metathesis applications. Interestingly, this strategy offered substantial improvement over the state of the art, with the efficient synthesis of the macrocyclic Exaltolide 2 at low catalyst loading and dilution conditions.

Ruthenium-based complexes containing a benzimidazolium tag covalently connected to N-heterocyclic carbene ligands: environmentally friendly catalysts for olefin metathesis transformations

Two ruthenium-based pre-catalysts containing an ionic tag covalently connected to a N-heterocyclic carbene (NHC) ligand are reported. These novel complexes, bearing a polar benzimidazolium group, are air-stable and can be easily prepared from commercially available reagents. The quaternary benzimidazolium tag allows the efficient separation of ruthenium waste from the metathesis product after reaction. Application in several olefin metathesis transformations leads to desired products of high purity, which exhibit ruthenium contamination levels as low as 1 ppm after simple filtration through a pad of silica gel.

Synthesis and Characterization of Sterically Enlarged Hoveyda‐Type Olefin Metathesis Catalysts

AbstractA series of four ruthenium‐based olefin metathesis catalysts has been prepared. These new complexes were designed with nanofiltration in organic media in mind; steric enlargement and functionalisation by means of polar ethylene glycol chains were incorporated. New complexes based on the stable 2nd generation Hoveyda‐type architecture and featuring substitution either on the NHC backbone or on the N‐aryl substituent of the NHC have been prepared and fully characterized. The application of these complexes in a series of olefin metathesis transformations revealed that these modified catalysts retained activity on par with the parent Hoveyda catalyst thus validating the disclosed ligand design.

Microwave‐Assisted Ruthenium‐Catalysed Olefin Metathesis in Fluorinated Aromatic Hydrocarbons: A Beneficial Combination

AbstractHigh conversions in ruthenium‐based olefin metathesis of demanding substrates are commonly forced by using a high loading of a catalyst and conducting reactions at elevated temperature for extended times. However, in many cases this approach is not fully effective. In this article we present that fluorinated aromatic hydrocarbons (FAH) combined with microwave (MW) irradiation using a commercially available ruthenium‐based pre‐catalyst creates attractive reaction conditions for promoting challenging olefin metathesis transformations.

New library of aminosulfonyl-tagged Hoveyda–Grubbs type complexes: Synthesis, kinetic studies and activity in olefin metathesis transformations

Seven novel Hoveyda–Grubbs precatalysts bearing an aminosulfonyl function are reported. Kinetic studies indicate an activity enhancement compared to Hoveyda’s precatalyst. A selection of these catalysts was investigated with various substrates in ring-closing metathesis of dienes or enynes and cross metathesis. The results demonstrate that these catalysts show a good tolerance to various chemical functions.

ChemInform Abstract: Chemoselective Olefin Metathesis Transformations Mediated by Ruthenium Complexes

AbstractReview: 72 refs.

Chemoselective olefin metathesis transformations mediated by ruthenium complexes

Over the past decade, ruthenium-mediated metathesis transformations, including polymerization reactions, cross-metathesis, ring-closing metathesis, enyne metathesis, ring-rearrangement metathesis, and also tandem processes, represent one of the most studied families of organic reactions. This has translated into the development of a large number of structurally diverse catalysts. Whereas most of these investigations are focused on determining catalytic performance, only rare examples of studies dealing with chemoselectivity have been reported to date. Usually, variations are observed in product conversions but rarely in product distributions. In this critical review, we provide an overview of the stereochemistry of newly formed C=C bonds either in ring-closing or cross-metathesis as a function of the catalyst structure. A discussion of disparities encountered in macrocyclisation reactions leading (or not) to the formation of dimeric products is also presented. Since distinctive metathesis products could be isolated as a function of the ligand borne by the ruthenium centre--phosphine or N-heterocyclic carbene in the dissymetrization of trienes, enyne metathesis and ring rearrangements, these topics are also discussed (72 references).

Dimethyl Carbonate: An Eco‐Friendly Solvent in Ruthenium‐Catalyzed Olefin Metathesis Transformations

Dimethyl Carbonate: An Eco‐Friendly Solvent in Ruthenium‐Catalyzed Olefin Metathesis Transformations

Enhancement of Enantioselectivity by THF in Asymmetric Mo‐Catalyzed Olefin Metathesis. Catalytic Enantioselective Synthesis of Cyclic Tertiary Ethers and Spirocycles.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Enhancement of enantioselectivity by THF in asymmetric mo-catalyzed olefin metathesis. Catalytic enantioselective synthesis of cyclic tertiary ethers and spirocycles.

Mo-catalyzed enantioselective rearrangement of achiral cyclopentenyl tertiary ethers to chiral cyclohexenyl tertiary ethers are reported. These olefin metathesis transformations proceed efficiently and with high levels of enantioselectivity. A noteworthy feature of these reactions is that added tetrahydrofuran exerts a remarkably positive influence on the enantioselectivity of the metathesis-based rearrangement. The first examples of catalytic asymmetric synthesis of spirocyclic structures by enantioselective olefin metathesis are also disclosed.