Search Results (86)

Carbonyl–olefin metathesis is an important reaction for the formation of new carbon–carbon bonds, specifically double bonds. This critical review presents an overview of the different possibilities of these reactions, highlighting their use in the synthesis of natural products. It features classical photochemical approaches via [2+2]-cycloadditions, early metal-mediated reports, and emerging catalytic methods through the use of organocatalysts or Lewis or Brønsted acids. Comparisons between methods are presented throughout the text, based primarily on robustness, selectivity, methodology, experimental simplicity, and utilization in the synthesis of natural products. Full article

The metathesis reaction between carbonyl compounds and olefins has emerged as a potent strategy for facilitating swift functional group interconversion and the construction of intricate organic structures through the creation of novel carbon–carbon double bonds. To date, significant progress has been made in carbonyl–olefin metathesis reactions, where oxetane, pyrazolidine, 1,3-diol, and metal alkylidene have been proved to be key intermediates. Recently, several reviews have been disclosed, focusing on distinct catalytic approaches for achieving carbonyl–olefin metathesis. However, the summarization of cyclization strategies for constructing aromatic heterocyclic frameworks through carbonyl–olefin metathesis reactions has rarely been reported. Consequently, we present an up-to-date review of the cyclization strategies in carbonyl–olefin metathesis, categorizing them into three main groups: the formation of monocyclic compounds, bicyclic compounds, and polycyclic compounds. This review delves into the underlying mechanism, scope, and applications, offering a comprehensive perspective on the current strength and the limitation of this field. Full article

Development of biobased aliphatic polyesters with better mechanical (tensile) properties in film has attracted considerable attention. This report presents the synthesis of soluble network biobased aliphatic polyesters by acyclic diene metathesis (ADMET) polymerization of bis(undec-10-enyl)isosorbide diester [M1, dianhydro-D-glucityl bis(undec-10-enoate)] in the presence of a tri-arm crosslinker [CL, glycerol tris(undec-10-enoate)] using a ruthenium–carbene catalyst, and subsequent olefin hydrogenation using RhCl(PPh₃)₃. The resultant polymers, after hydrogenation (expressed as HCP1) and prepared in the presence of 1.0 mol% CL, showed better tensile properties than the linear polymer (HP1) with similar molecular weight [tensile strength (elongation at break): 20.8 MPa (282%) in HP1 vs. 35.4 MPa (572%) in HCP1]. It turned out that the polymer films prepared by the addition of CL during the polymerization (expressed as a 2-step approach) showed better tensile properties. The resultant polymer film also shows better tensile properties than the conventional polyolefins such as linear high density polyethylene, polypropylene, and low density polyethylene. Full article

The molybdenum-catalyzed enantioselective ring-closing metathesis/kinetic resolution of a series of racemic planar-chiral 1,1′-diallylferrocene derivatives was reinvestigated utilizing the method of generating catalytically active chiral molybdenum-alkylidene species in situ, which allowed us to examine a variety of chiral molybdenum-alkylidene metathesis precatalysts in the present asymmetric reaction. With the catalyst screening experiments conducted in this study, the more practical reaction conditions, including a choice of a proper chiral molybdenum precatalyst, giving planar-chiral ferrocenes of higher enantiomeric purity and better chemoselectivity could be optimized. Full article

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. Full article

Recently discovered cis-dichloro benzylidene phosphite complexes are latent catalysts at room temperature and exhibit exceptional thermal and photochemical activation behavior in olefin metathesis reactions. Most importantly, the study of these catalysts has allowed their introduction in efficient 3-D printing applications of ring-opening metathesis derived polymers and the control of chromatically orthogonal chemical processes. Moreover, their combination with plasmonic Au-nanoparticles has given rise to novel smart materials that are responsive to light. Given the importance of the ligand shell in the initiation and reactivity behavior of this family of complexes, we set out to investigate the effect of anionic ligand exchange. Thus, we report herein two new ruthenium benzylidene benzylphosphite complexes where the chloride anionic ligands have been replaced by bromide and iodide anions (cis-Ru-Phos-Br₂ & cis-Ru-Phos-I₂). The thermal and photochemical activations of these dormant catalysts in a variety of ring-closing and ring-opening metathesis polymerization (RCM and ROMP) reactions were thoroughly studied and compared with the previously known chloride precatalyst. Photochemical RCM studies provided similar results, especially in non-hindered reactions, with the UV-A wavelength being the best in all cases. On the other hand, the thermal activation profile exposed that the anionic ligand significantly affects reactivity. Notably, cis-Ru-Phos-I₂ disclosed particularly impressive initiation efficiency compared to the other members of the family. Full article

Recently, sterically demanding N-heterocyclic cyclometalated ruthenium were reported as efficient Z-selective catalysts for cross-metathesis, showing a different reactivity in the function of the auxiliary ligand and the bulky ligand. To understand the origin of this behavior, we carried out density functional (M06-L) calculations to explore the reaction mechanism and insight from the energetic contributions into the determinant step. We emphasize the differences that occur when the 2,6-diisopropylphenyl (Dipp) and 2,6-diisopentylphenyl (Dipep) are employed. The results show that the barrier energies, $\Delta G^{‡}$, increase when the bulky ligand is greater, using nitrate as an auxiliary ligand, while the opposite behavior is obtained when pivalate is the auxiliary ligand. This tendency has its origin in the low reorganization energy and the less steric hindrance (%V_bur) obtained in catalysts that involve nitrate ligand and Dipep group. Moreover, by scrutinizing the energy decomposition analysis (EDA), it is found that the electronic contributions are also dominant and are not uniquely the steric effects that control the Z-selectivity. Full article

The applicability of linear model predictive control to the 2-butene metathesis process is studied. Similarly to industrial practice, the model predictive controller is configured on a supervisory level, providing set points to basic process controllers. The development of the process model is based on open-loop identification from input–output data extracted from dynamic simulation performed in Aspen Plus Dynamics. The model predictive controller, designed using MATLAB tools, supervises a system consisting of two inputs (feed rate and reaction temperature) and two outputs (ethylene and propylene production rates). The performance of the model-based control strategy is assessed by Aspen Plus Dynamics-Simulink co-simulation and compared to regulatory control through several indexes (mean square error, integral square error, peak error, and integral absolute error). The model predictive controller outperforms the feedback controller. Considerations regarding the workflow for the implementation of model predictive control in an industrial environment are provided. Full article

Ruthenium-catalyzed cross metathesis using biseugenol (1) with electron-deficient olefins methyl (2a) and ethyl (2b) acrylates, acrylic acid (2c), acrylonitrile (2d), and methyl methacrylate (2e) derivatives have been conducted to afford respective derivatives 3a–3e with good yields and excellent conversion rates. Activity of prepared compounds against trypomastigote and amastigote forms of Trypanosoma cruzi and mammalian cytotoxicity have been evaluated. The results obtained indicate that the IC₅₀ values for amastigotes of compounds 3b and 3d are quite similar to those of biseugenol (1), but unlike this compound, they show reduced toxicities with SI values similar to those of the standard drug benznidazol. Full article

Recombinant peptide synthesis allows for large-scale production of peptides with therapeutic potential. However, access to dicarba peptidomimetics via sidechain-deprotected sequences becomes challenging with exposed Lewis basicity presented by amine and sulfur-containing residues. Presented here is a combination of strategies which can be used to deactivate coordinative residues and achieve high-yielding Ru-catalyzed ring-closing metathesis. The chemistry is exemplified using α-conotoxin EpI, a native bicyclic disulfide-containing sequence isolated from the marine conesnail Conus episcopatus. Replacement of the loop I disulfide with E/Z–dicarba bridges was achieved with high conversion via solution-phase ring-closing metathesis of the unprotected linear peptide after simple chemoselective oxidation and ion-exchange masking of problematic functionality. Metathesis was also attempted in green solvent choices to further improve the sustainability of dicarba peptide synthesis. Full article

One of the most effective synthetic pathways to produce unsaturated compounds and polymers, meant for both industrial and pharmaceutical applications, is olefin metathesis. These useful reactions are commonly promoted by ruthenium-based precatalysts, namely the second-generation Grubbs’ catalyst (GII) and complexes bearing a styrenyl ether ligand, referred to as the second-generation Hoveyda–Grubbs’ catalyst (HGII). By altering the steric and electronic characteristics of substituents on the backbone and/or on the nitrogen atoms of the NHC ligand, it is possible to increase the reactivity and stability of second-generation ruthenium catalysts. The synthesis of an HG type II complex bearing two anti-phenyl backbone substituents (anti-HGII_Ph-Mes) with mesityl N-substituents is reported. The catalytic performances of the new complex were investigated in standard ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROMP) and compared to those of the analogue complex syn-HGII_Ph-Mes and to the classic HGII complex. A thorough analysis of the temperature dependence of the performances, along with a detailed comparison with the commercially available HGII, is conducted. The HGII_Ph-Mes complexes are more thermally stable than their parent HGII, as shown by the fact that their activity in the ROMP of 5-ethylidene-2-norbornene does not alter when the polymerization is carried out at room temperature after the complexes have been held at 180 °C for two hours, making them particularly interesting for materials applications. Full article

This article considers the design and control of the 2-butene metathesis process. The process transforms a low-value feedstock derived from a fluid catalytic cracking unit into more valuable products. The economical optimization is applied to the preheat–reaction and separation sections, with the objective of minimizing the total annual cost. The dynamic response and control of the plant are evaluated for feed flow perturbations. Although the process control system acts as a first line of defense against potential hazards, other independent safety layers are discussed with safety limits specific to the critical equipment of the 2-butene metathesis unit. The results prove that the metathesis reaction of 2-butene over a mesoporous tungsten catalyst is economically attractive. For a 5.7 t/h feed rate consisting of 2-butene (70% molar) and n-butane (30% molar), a reaction–separation plant (without recycle) requires 6570 × 10³ $ investment and has a profitability of 2300 × 10³ $/year. Full article

The olefin metathesis reaction has found numerous applications in organic synthesis. This is due to a number of advantages, such as the tolerance of most functional groups and sterically demanding olefins. This article reviews recent advances in the application of the metathesis reaction, particularly the metathetic cyclization of dienes and enynes, in synthesis protocols leading to (hetero)aromatic compounds. Full article

Two new unsymmetrical N-heterocyclic carbene ligand (uNHC)-based ruthenium complexes featuring phenolic OH function were obtained and fully characterised. The more active one was then immobilised on the metal–organic framework (MOF) solid support (Al)MIL-101-NH₂. The catalytic activity of such a heterogeneous system was tested, showing that, while the heterogeneous catalyst is less active than the corresponding homogeneous catalyst in solution, it can catalyse selected olefin metathesis reactions, serving as the proof-of-concept for the immobilisation of catalytically active complexes in MOFs using a phenolic tag. Full article

Phosphine-free ruthenium benzylidene complexes containing imidazole ligands are reported. These catalysts are effective for ring-closing metathesis (RCM) and cross-metathesis (CM) reactions at high temperatures, where the more widely used phosphine-containing N-heterocyclic carbene-based ruthenium catalysts show side reactions. This discovery opens up a pathway to develop more selective ruthenium metathesis catalysts for reactions requiring harsh conditions. Full article