Olefin Metathesis Research Articles

Alkene Cross-Metathesis with 2,5-Dimethyl-2,4-Hexadiene Enables Isobutylenyl / Prenyl Functionalizations and Rubber Valorization.

2,5-Dimethyl-2,4-hexadiene is a readily available and easily managable compound, whose symmetric and polymethylated dienic structure should be prone to engage in cross-metathesis reactions with other alkenes, but this has not been apparently exploited so far. Here we show that this reactant enables the easy synthesis of tri- and tetra-susbtituted alkenes (i.e. isobutylenyl and prenyl groups) from simple alkenes under mild reaction conditions, not only with the conventional 2nd generation Grubbs catalyst but also with other Grela-type catalysts such as StickyCat,TM AquaMetTM and GreenCat.TM The use of liquid and low volatile 2,5-dimethyl-2,4-hexadiene avoids the use of gaseous alkene reactants and, besides, showcases the reactivity of polyisoprene (rubber), thus allowing to optimize the reaction conditions for rubber upcycling, after metathesis reaction of the pristine or used polymer with simple alkenes. These results bring low volatile isoprene-type compounds as privileged poly-substituted reactants for alkene cross-metathesis reactions.

Tandem Olefin Metathesis Polymerization to Access Degradable and Recyclable Thermosets, Thermoplastics, and Elastomers

Tandem Olefin Metathesis Polymerization to Access Degradable and Recyclable Thermosets, Thermoplastics, and Elastomers

Recent Synthesis of Nucleoside Phosphonate Analogs Using Olefin Cross-metathesis.

Nucleotide analogs known as acyclic and cyclic nucleoside phosphonates (ANPs and CNPs, respectively) have a variety of biological properties, including antibacterial, antiviral, antiparasitic, antineoplastic, and immunomodulatory. A strong reaction that has emerged in the last several decades has fundamentally changed our knowledge of the chemistry of nucleoside phosphonates. In particular, Olefin cross-metathesis (CM) has been a potent and practical synthesis route to produce functionalized olefins from essential alkene precursors. This review describes recent synthesis examples of ANPs and CNPs analogs using the Ru-catalyzed olefin cross-metathesis reactions. Olefin cross-metathesis reactions are performed in the olefinic parts of nucleoside and phosphonate produced by Grubbs, Hoveyda-Grubbs, and Nolan. This review presents a synthetic overview of a few chosen nucleosides with biological significance. Their biological activity results are briefly discussed.

Synthetic Approach toward Diverse Oxa-Cages via Olefin Metathesis.

This article demonstrates a late-stage modification of the cage propellanes that are transformed into intricate oxa-cycles via ring-rearrangement metathesis (RRM) and regioselective ring-closing metathesis (RCM) as crucial steps. In addition, we also report the extended pentacycloundecane (PCUD)-based oxa-cages involving the domino cycloetherification followed by olefin metathesis. These oxa-cages involve a domino sequence in which the PCUD core unit remains intact. [Ru]-based Grubbs catalysts are used to execute the metathesis step to assemble these higher-order oxa-cage systems. Spectroscopic data assigned structures of various products and were further supported by single-crystal X-ray diffraction analysis. The synthetic approach to these cage polycycles involves high complexity generating processes such as Diels-Alder reaction, [2 + 2] photocycloaddition, and RRM as well as RCM.

Metathetic degradation of waste vulcanized emulsion type butadiene-based rubber

Metathetic degradation has been recognized as promising strategy for the treatment of waste vulcanized rubbers as a Waste-to-Resources approach, not only eliminating the pollution but also recycling as resources. However, it was mainly used for the treatment of the waste vulcanized natural rubber, which contains plentiful cis-1,4- structure. Despite of a much higher consumption of the emulsion type butadiene-based rubbers than natural rubber, there was no report on the metathetic degradation of the waste vulcanized emulsion type butadiene-based rubbers due to their less cis-1,4- unit, although the metathetic functionalization of the nonvulcanized emulsion type butadiene-based rubbers have been well reported. Here, the metathetic degradation of waste vulcanized emulsion type butadiene-based rubber was explored with nitrile-butadiene rubber (NBR) glove as a model. Different from the metathetic degradation of waste vulcanized natural rubber via only cross metathesis between cis-1,4-structure and the chain transfer agent (CTA), the ring closing metathesis between the adjacent cis-1,4-structure and 1,2-structure also occurred in the metathetic degradation of waste vulcanized NBR. It is expected to open the door for the Waste-to-Resources approach of all waste vulcanized emulsion type diene-based rubbers.

PhotoROMP: The Future Is Bright.

Since the earliest investigations of olefin metathesis catalysis, light has been the choice for controlling the catalyst activity on demand. From the perspective of energy efficiency, temporal and spatial control, and selectivity, photochemistry is not only an attractive alternative to traditional thermal manufacturing techniques but also arguably a superior manifold for advanced applications like additive manufacturing (AM). In the last three decades, pioneering work in the field of ring-opening metathesis polymerization (ROMP) has broadened the scope of material properties achievable through AM, particularly using light as both an activating and deactivating stimulus. In this Perspective, we explore trends in photocontrolled ROMP systems with an emphasis on approaches to photoinduced activation and deactivation of metathesis catalysts. Recent work has yielded a myriad of commercial and synthetically accessible photosensitive catalyst systems, although comparatively little attention has been paid to achieving precise control over polymer morphology using light. Metal-free, photophysical, and living ROMP systems have also been relatively underexplored. To take fuller advantage of both the thermomechanical properties of ROMP polymers and the operational simplicity of photocontrol, clear directions for the field are to improve the reversibility of activation and deactivation strategies as well as to further develop photocontrolled approaches to tuning cross-link density and polymer tacticity.

Novel Pyridyl Macrocyclic Triarylmethanes: Synthesis by Ring-closing Metathesis and Chemical Analysis

Background:: Nowadays, macrocyclic compounds constitute a privileged source for the development of compounds with interesting biological properties. Ring-closing olefin me-tathesis has received great attention for the synthesis of small, medium, and larger ring systems. Methods:: In the present work, we described the synthesis of eight original pyridyl macrocyclic triarylmethanes using an efficient 3-step synthetic strategy. The bisalkylated 4,4'-(pyridin-X-ylmethylene) diphenols (X=2-4) were prepared by ring-closing metathesis as macrocyclization key step, using Grubbs second generation catalyst. Results:: The pyridyl macrocyclic triarylmethanes were obtained with moderate to good yields. The introduction of a pyridine N-oxide moiety before the macrocyclization proved to be interest-ing to afford a higher yield of the corresponding metathesis product. FT-IR, 1 H NMR, 13C NMR, and X-ray diffraction analysis have been used for the characterization of the synthesized compounds. Conclusion:: The synthetic strategy used here proposes an efficient alternative to prepare macro-cyclic triarylmethanes of different sizes.

Role of Surface Silanols in Active Site Formation during Olefin Metathesis over a WOx/SiO2 Catalyst: A Computational Perspective

Role of Surface Silanols in Active Site Formation during Olefin Metathesis over a WO_<i>x</i>/SiO₂ Catalyst: A Computational Perspective

Designing Degradable Polymers from Tricycloalkenes via Complete Cascade Metathesis Polymerization.

Cascade metathesis polymerization has been developed as a promising method to synthesize complex but well-defined polymers from monomers containing multiple reactive functional groups. However, this approach has been limited to the monomers involving simple alkene/alkyne moieties or produced mainly non-degradable polymers. In this study, we demonstrate a complete cascade ring-opening/ring-closing metathesis polymerization (RORCMP) using various tricycloalkenes and two strategies for the efficient degradation. Through rational design of tricycloalkene monomers, the structure and reactivity relationship was explored. For example, tricycloalkenes with trans configuration in the central ring enabled faster and better selective cascade RORCMP than the corresponding cis isomers. Also, a 4-substituted cyclopentene moiety in the monomers significantly enhanced the overall cascade RORCMP performance, with the maximum turnover number (TON) reaching almost 10,000 and molecular weight up to 170 kg/mol using an amide-containing monomer. Furthermore, we achieved one-shot cascade multiple olefin metathesis polymerization using tricycloalkenes and a diacrylate, to produce new highly A,B-alternating copolymers with full degradability. Lastly, we successfully designed xylose-based tricycloalkenes to give well-defined polymers that underwent ultra-fast and complete degradation under mild conditions.

Designing Degradable Polymers from Tricycloalkenes via Complete Cascade Metathesis Polymerization

AbstractCascade metathesis polymerization has been developed as a promising method to synthesize complex but well‐defined polymers from monomers containing multiple reactive functional groups. However, this approach has been limited to the monomers involving simple alkene/alkyne moieties or produced mainly non‐degradable polymers. In this study, we demonstrate a complete cascade ring‐opening/ring‐closing metathesis polymerization (RORCMP) using various tricycloalkenes and two strategies for the efficient degradation. Through rational design of tricycloalkene monomers, the structure and reactivity relationship was explored. For example, tricycloalkenes with trans configuration in the central ring enabled faster and better selective cascade RORCMP than the corresponding cis isomers. Also, a 4‐substituted cyclopentene moiety in the monomers significantly enhanced the overall cascade RORCMP performance, with the maximum turnover number (TON) reaching almost 10,000 and molecular weight up to 170 kg/mol using an amide‐containing monomer. Furthermore, we achieved one‐shot cascade multiple olefin metathesis polymerization using tricycloalkenes and a diacrylate, to produce new highly A,B‐alternating copolymers with full degradability. Lastly, we successfully designed xylose‐based tricycloalkenes to give well‐defined polymers that underwent ultra‐fast and complete degradation under mild conditions.

Cyclodextrin‐Based Catenanes Platformed with meso‐Arylporphyrin

AbstractAmong mechanically interlocked supramolecular systems with cyclodextrins (CDs), successful examples of CD‐based catenanes are limited compared to a number of CD rotaxanes owing to the synthetic difficulties. We herein demonstrate an efficient synthesis of a CD‐based catenane using a meso‐arylporphyrin (Por) platform. Using Por modified with two olefin‐terminated oxyethylene chains at the cis‐meso‐positions, an interlocked Por‐CD catenane was synthesized via olefin metathesis in the presence of per‐O‐methylated β‐CD (TMe‐β‐CD) in water. The novel Por‐CD catenane was obtained in 30 % isolated yield, which was characterized by MALDI‐TOF mass and NMR spectroscopies. In the latter part, we demonstrate determination of the binding constants between TMe‐β‐CD and meso‐(4‐sulfonatophenyl)porphyrin using Por‐CD catenane, 2,6‐di‐O‐methyl‐β‐CD (DMe‐β‐CD), and 13C‐labeled TMe‐β‐CD (13C‐TMe‐β‐CD). The host‐guest exchange reaction from the Por‐CD catenane/DMe‐β‐CD to the Por‐CD catenane/TMe‐β‐CD complexes was directly monitored through 1D HMQC spectroscopy. The ratio of these complexes revealed the difference in the binding affinities of DMe‐β‐CD and TMe‐β‐CD to Por. The stable 1 : 2 inclusion complex between meso‐tetrakis(4‐sulfonatophenyl)porphyrin (TPPS) and TMe‐β‐CD has been well‐studied for many years. This study is the first to determine the respective binding constants, K1 and K2, using the model system, to be 3.0×107 M−1 and 3.4×107 M−1, respectively.

Rhenium Alkyne Catalysis: Sterics Control the Reactivity.

Metathesis reactions, including alkane, alkene, and alkyne metatheses, have their origins in the fundamental understanding of chemical reactions and the development of specialized catalysts. These reactions stand as transformative pillars in organic chemistry, providing efficient rearrangement of carbon-carbon bonds and enabling synthetic access to diverse and complex compounds. Their impact spans industries such as petrochemicals, pharmaceuticals, and materials science. In this work, we present a detailed mechanistic study of the Re(V) catalyzed alkyne metathesis through density functional theory calculations. Our findings are in agreement with the experimental evidence from Jia and co-workers and unveil critical factors governing catalyst performance. Our work not only enhances our understanding of alkyne metathesis but also contributes to the broader landscape of catalytic processes, facilitating the design of more efficient and selective transformations in organic synthesis.

Pursuing E-Selective Olefin Metathesis: Tuning Steric and Electronic Properties of S,N-Chelated Ruthenium Alkylidenes

Pursuing <i>E</i>-Selective Olefin Metathesis: Tuning Steric and Electronic Properties of S,N-Chelated Ruthenium Alkylidenes

Ruthenium Complexes with a Tridentate Anionic Bisfluoroalkoxy‐Carbene Ligand – Valuable Latent Olefin Metathesis Catalysts for Polymerisation Reactions

AbstractA Grubbs‐type ruthenium complex bearing a tridentate anionic bisfluoroalkoxy‐carbene was synthesised and fully characterised. Under standard conditions, it proved to be inactive in olefin metathesis reactions, but the addition of HCl triggers its activity and allows the synthesis of a series of cyclic olefins and ethers as well as a stereoregular polynorbornene with an unexpectedly high content of trans‐configured double bonds, as found in commercially available polynorbornene (Norsorex®). Detailed structural studies and DFT calculations showed that the complex enters the catalytic cycle, but instead of performing a full turnover, it is caught as a stable intermediate that does not undergo further reactions. The addition of HCl causes dissociation of the fluoroalkoxy units, resulting in a compound that behaves similarly to standard Grubbs‐type complexes. To further understand this phenomenon, the corresponding Hoveyda‐Grubbs complex was also obtained and studied in detail; due to the absence of the phosphine ligand, its behaviour was different from that of its Grubbs‐type counterpart.

Olefin Metathesis and Stereoselective Ring-Opening Metathesis Polymerization with Neutral and Cationic Molybdenum(VI) Imido and Tungsten(VI) Oxo Alkylidene Complexes Containing N-Chelating N-Heterocyclic Carbenes

Olefin Metathesis and Stereoselective Ring-Opening Metathesis Polymerization with Neutral and Cationic Molybdenum(VI) Imido and Tungsten(VI) Oxo Alkylidene Complexes Containing N-Chelating N-Heterocyclic Carbenes

Direct Synthesis of Aryloxy Phosphonamidate Nucleotide Prodrugs Using the Cross Metathesis Assisted by Ultrasonic Irradiation.

A direct synthetic strategy of aryloxy phosphonamidate nucleotide prodrugs (A, G, C, and U) was developed with the CM reaction assisted by ultrasonic irradiation and partitioned addition of 12 mol % of Hoveyda-Grubbs (H-G) II catalyst in 61-82% yields as a mixture of E-/Z-isomers (∼2:1) from aryloxy vinylphosponamidate and 5'-vinyl nucleoside moieties.

Synthesis and Characterization of Dearomatized Pyridine‐Derived Alkyl‐Amido‐tert‐Butylphosphine Iron(II) Complexes

AbstractNeutral three‐coordinate iron alkylidenes of the form PN−Fe=CHR have been proposed as viable candidates for alkene metathesis. Indeed, during the final stages of preparing this current study, a separate report disclosed that dearomatized PN−Fe‐alkyl complexes are active precatalysts for ring‐opening metathesis polymerization (ROMP) of norbornene implicating PN−Fe=CHR species as possible intermediates. In yet another separate report, we prepared Zn analogues of PN−Fe‐alkyl complexes and herein provide an account for the synthesis, characterization, and reactivity of some new iron complexes with the same tBu substituted PN platform.

Is Mn(I) More Promising Than Fe(II)-A Comparison of Mn vs Fe Complexes for Olefin Metathesis.

Olefin metathesis is one of the most significant transformations in organic chemistry and is an excellent example for efficient homogeneous catalysis. Although most currently used catalysts are primarily based on 4d and 5d metals, cycloaddition and cycloreversion reactions can also be attributed to first-row transition metals, such as Fe. Surprisingly, the potential of Mn(I)-based catalysts for olefin metathesis has been unexplored despite their prominence in homogeneous catalysis and their diagonal relationship to Ru(II). In the present study, we have investigated the prospective capabilities of Mn complexes for cycloaddition and reversion reactions using density functional theory. Therefore, we have initially compared the literature known iron model systems and their isoelectronic Mn counterparts regarding their reactivity and electronic structure. Next, we constructed potential Mn complexes derived from synthetically accessible species, including carbonyl ligands and obeying octahedral geometry. Based on thermodynamic parameters and the calculation of electronic descriptors, we were able to validate the isodiagonal relationship. Our study serves as guidance for the experimental chemist.

Synthesis of Biomimetic Thioesters for Studies of Ketoreductase Domains from the Biosynthesis of Cytotoxic Polyketides

AbstractThe synthesis of biomimetic thioesters for enzymatic studies of ketoreductase (KR) domains from polyketide synthases is described. A TBS-protected dihydroxyalkene fragment was synthesised by a sequence involving a Nagao acetate aldol reaction, a Mukaiyama propionate aldol reaction, and a methylene Wittig olefination. Fragment coupling to N-acetylcysteamine (SNAC) (E)-3-hydroxyhex-4-enethioates by an olefin cross-metathesis (OCM) and subsequent deprotection gave the potential KR product stereoisomers. An analogous OCM with a SNAC (E)-3-ketohex-4-enethioate did not give the desired KR precursor, but the reaction could successfully be replaced by a Horner–Wadsworth–Emmons olefination between a SNAC 3-ketothioester phosphonate and a TBS-protected dihydroxy aldehyde. After deprotection, an intramolecular cyclisation was observed that needs to be considered as a spontaneous side reactivity in the enzymatic assays.

Recent Developments in Synthesis, Properties, Applications and Recycling of Bio-Based Elastomers.

In 2021, global plastics production was 390.7 Mt; in 2022, it was 400.3 Mt, showing an increase of 2.4%, and this rising tendency will increase yearly. Of this data, less than 2% correspond to bio-based plastics. Currently, polymers, including elastomers, are non-recyclable and come from non-renewable sources. Additionally, most elastomers are thermosets, making them complex to recycle and reuse. It takes hundreds to thousands of years to decompose or biodegrade, contributing to plastic waste accumulation, nano and microplastic formation, and environmental pollution. Due to this, the synthesis of elastomers from natural and renewable resources has attracted the attention of researchers and industries. In this review paper, new methods and strategies are proposed for the preparation of bio-based elastomers. The main goals are the advances and improvements in the synthesis, properties, and applications of bio-based elastomers from natural and industrial rubbers, polyurethanes, polyesters, and polyethers, and an approach to their circular economy and sustainability. Olefin metathesis is proposed as a novel and sustainable method for the synthesis of bio-based elastomers, which allows for the depolymerization or degradation of rubbers with the use of essential oils, terpenes, fatty acids, and fatty alcohols from natural resources such as chain transfer agents (CTA) or donors of the terminal groups in the main chain, which allow for control of the molecular weights and functional groups, obtaining new compounds, oligomers, and bio-based elastomers with an added value for the application of new polymers and materials. This tendency contributes to the development of bio-based elastomers that can reduce carbon emissions, avoid cross-contamination from fossil fuels, and obtain a greener material with biodegradable and/or compostable behavior.