Ruthenium-based Olefin Metathesis Catalysts Research Articles

Boosting the Efficiency and Stability of Li-CO2 Batteries via a Ruthenium-Based Olefin-Metathesis Catalyst.

The practical application of Li-CO2 batteries is significantly hindered by high charge potential and short lifespan, mainly due to sluggish reaction kinetics and inadequate reaction reversibility. Homogeneous catalysts added to the electrolyte provide a promising strategy to address these issues. In this work, the third-generation Grubbs catalyst (G-III), which is efficient for olefin metathesis reactions, has been adopted as a homogeneous catalyst for Li-CO2 batteries. Batteries with G-III exhibited a low overpotential of 0.86 V and a lifespan of 1300 h at a current density of 300 mA g-1. Even at a high current density of 2000 mA g-1, the batteries remained stable for over 300 cycles, with an initial overpotential of 1.11 V. A two-step discharge/charge reaction involving Li2C2O4 as an intermediate was well illustrated, attributed to both low overpotentials and high specific capacity. These findings provide insights into catalyst selection and mechanism analysis for Li-CO2 batteries, offering practical strategies for Li-CO2 battery performance enhancement and practical applications.

Automated de Novo Design of Olefin Metathesis Catalysts: Computational and Experimental Analysis of a Simple Thermodynamic Design Criterion.

Methods for computational de novo design of inorganic molecules have paved the way for automated design of homogeneous catalysts. Such studies have so far relied on correlation-based prediction models as fitness functions (figures of merit), but the soundness of these approaches has yet to be tested by experimental verification of de novo-designed catalysts. Here, a previously developed criterion for the optimization of dative ligands L in ruthenium-based olefin metathesis catalysts RuCl2(L)(L')(═CHAr), where Ar is an aryl group and L' is a phosphine ligand dissociating to activate the catalyst, was used in de novo design experiments. These experiments predicted catalysts bearing an N-heterocyclic carbene (L = 9) substituted by two N-bound mesityls and two tert-butyl groups at the imidazolidin-2-ylidene backbone to be promising. Whereas the phosphine-stabilized precursor assumed by the prediction model could not be made, a pyridine-stabilized ruthenium alkylidene complex (17) bearing carbene 9 was less active than a known leading pyridine-stabilized Grubbs-type catalyst (18, L = H2IMes). A density functional theory-based analysis showed that the unsubstituted metallacyclobutane (MCB) intermediate generated in the presence of ethylene is the likely resting state of both 17 and 18. Whereas the design criterion via its correlation between the stability of the MCB and the rate-determining barrier indeed seeks to stabilize the MCB, it relies on RuCl2(L)(L')(═CH2) adducts as resting states. The change in resting state explains the discrepancy between the prediction and the actual performance of catalyst 17. To avoid such discrepancies and better address the multifaceted challenges of predicting catalytic performance, future de novo catalyst design studies should explore and test design criteria incorporating information from more than a single relative energy or intermediate.

Plasmonic visible-near infrared photothermal activation of olefin metathesis enabling photoresponsive materials.

Light-induced catalysis and thermoplasmonics are promising fields creating many opportunities for innovative research. Recent advances in light-induced olefin metathesis have led to new applications in polymer and material science, but further improvements to reaction scope and efficiency are desired. Herein, we present the activation of latent ruthenium-based olefin metathesis catalysts via the photothermal response of plasmonic gold nanobipyramids. Simple synthetic control over gold nanobipyramid size results in tunable localized surface plasmon resonance bands enabling catalyst initiation with low-energy visible and infrared light. This approach was applied to the ROMP of dicyclopentadiene, affording plasmonic polymer composites with exceptional photoresponsive and mechanical properties. Moreover, this method of catalyst activation was proven to be remarkably more efficient than activation through conventional heating in all the metathesis processes tested. This study paves the way for providing a wide range of photoinduced olefin metathesis processes in particular and photoinduced latent organic reactions in general by direct photothermal activation of thermally latent catalysts.

Syntheses and Applications of Indol-2-ylidene-Ligated Ruthenium-Based Olefin Metathesis Catalysts

Ru-based catalysts bearing ambiphilic carbenes exhibit exceptionally high turnover numbers (TONs) in olefin metathesis reactions. However, the syntheses of these catalysts are still challenging because of the strong ambiphilicities of the carbenes. Herein, we prepared a family of indol-2-ylidene (IdY)-ligated Ru-based (Ru–IdY) olefin metathesis catalysts and obtained two X-ray crystal structures of Ru–IdY complexes showing a distinct conformation of the ruthenium centers. An exceptional stability of the complexes was demonstrated by a decomposition test conducted in deuterated benzene at 40 °C, indicating that approximately 98% of the most stable Ru–IdY catalyst was retained even after 3 weeks. The catalytic activities of Ru–IdY catalysts were investigated for ring-closing metathesis, ring-opening metathesis polymerization (ROMP), and ethenolysis. The most sterically accessible Ru–IdY catalyst, 2e, exhibited the best catalytic activity for ethenolysis (TON 61200 and selectivity for methyl oleate 95%; TON 53200 and selectivity for cis-cyclooctene 70%), whereas the sterically demanding catalyst 2f demonstrated the most efficient catalytic activity for ROMP in comparison to the other Ru–IdY catalysts, achieving a complete conversion in 2 min.

Fluorine-containing ruthenium-based olefin metathesis catalysts

The review summarizes literature data on the methods for the introduction of fluorine atoms and fluoralkyl groups into different ligands to construct metathesis-active ruthenium carbene complexes. It also analyzes the influence of fluorinated ligands on the catalytic activity of the complexes. The choice, structure and positions of fluorinated substituents in NHC ligands are generally dictated by the desire to increase the electrophilicity of the ruthenium atom due to the electron-withdrawing effect of fluorine atoms and fluoroalkyl groups, resulting, as a rule, in an increase in the activity of the ruthenium complex. In catalysts with unsymmetrical fluorine-containing NHC ligands, there is a possibility of additional Ru–F coordination, making the complexes much more stable and, consequently, more active. The presence of fluorine in chelating alkylidene ligands provides an increase in the catalyst initiation rate due to a weakening of the ruthenium – heteroatom bond. Besides, the introduction of polyfluoroalkyl groups into ligands solves the problem of catalyst recovery using fluorous biphasic systems for reuse.The bibliography includes 172 references.

Ethylene-Triggered Formation of Ruthenium Alkylidene from Decomposed Catalyst

Ethylene is known to readily decompose ruthenium-based olefin metathesis catalysts, such as Grubbs second-generation catalyst (GII), by forming the unsubstituted ruthenacyclobutane (Ru-2) that may undergo a 1,2-H shift and liberate propene. The resulting alkylidene loss has been assumed to be irreversible. Yet, by reacting (SIMes)(η6-p-cymene)RuCl2 (1), the p-cymene-stabilized alkylidene-free fragment resulting from loss of propene from Ru-2, with ethylene, we show that the methylidene analogue of GII (GIIm) and other Ru alkylidenes are formed, along with catalytic amounts of propene and butenes, and can be stabilized by tricyclohexylphosphine (PCy3) at 50 °C in C6D6. An almost 20-fold increase in activity for ring-closing metathesis of diethyl diallylmalonate (DEDAM) on pretreatment of 1 with ethylene suggests that the reversibility of the alkylidene loss may be used to develop longer-lived metathesis catalysts and processes. Mechanistic density functional theory (DFT) calculations suggest that the connection between 1 and GIIm involves oxidative coupling of two ethylene molecules to form a key metallacyclopentane intermediate (M49). A 1,2-H shift in M49 gives the methyl-substituted ruthenacyclobutane M303, which, on cycloreversion, liberates propene and GIIm. Alternatively, successive H-shifts starting in M49 may give 1-butene (fast reaction) and 2-butene (slower) with a lower barrier than that of Ru alkylidene. The lower predicted barrier is consistent with butene, especially 1-butene, being the dominating product at the start of the experiments, in particular at lower temperature.

Grubbs Catalyst 2nd Generation: Synthesis and Activity of Ruthenium-Based Olefin Metathesis Catalysts

Key words Grubbs catalysts - olefin metathesis - ruthenium catalysis - ring-closing metathesis

Vortex Fluidic Ethenolysis, Integrating a Rapid Quench of Ruthenium Olefin Metathesis Catalysts

Ruthenium-catalysed ethenolysis occurs in a vortex fluidic device (VFD) – a scalable, thin-film microfluidic continuous flow process. This process takes advantage of the efficient mass transfer of gaseous reagents into the dynamic thin film of liquid. Also reported is the rapid quenching of the ruthenium-based olefin metathesis catalyst by the addition of a saturated solution of N-acetyl-l-cysteine in MeCN, as a convenient alternative to previously reported quenching methods.

Ruthenium-based olefin metathesis catalysts with monodentate unsymmetrical NHC ligands.

An overview on the catalytic properties of ruthenium complexes for olefin metathesis bearing monodentate unsymmetrical N-heterocyclic diaminocarbene ligands is provided. The non-symmetric nature of these NHC architectures strongly influences activity and selectivity of the resulting catalysts. The main achievements that have been accomplished in significant areas of olefin metathesis up to the current state of research are discussed.

Carboxyl Graphene as a Superior Support for Bulky Ruthenium-Based Olefin Metathesis Catalyst

A Hoveyda-type catalyst decorated with two quaternary ammonium tags was synthesized and noncovalently grafted on SiO2, SBA-15, and on carboxyl graphene. A comparative study showed that the efficiency of the dual-anchored heterogeneous catalysts was highly dependent on the properties of the supporting material with graphene outperforming silicate supports. The graphene-immobilized complex exhibited excellent efficiency reflected in turnover numbers obtained in ring-closing metathesis and in self-metathesis of 1-decene. Importantly, the solid-supported catalyst assured increased recyclability with no ruthenium leaching as confirmed by inductively coupled plasma mass spectrometry.

Recent advances in ruthenium-based olefin metathesis.

Ruthenium-based olefin metathesis catalysts, known for their functional group tolerance and broad applicability in organic synthesis and polymer science, continue to evolve as an enabling technology in these areas. A discussion of recent mechanistic investigations is followed by an overview of selected applications.

Using stereoretention for the synthesis of E-macrocycles with ruthenium-based olefin metathesis catalysts.

The synthesis of E-macrocycles is achieved using stereoretentive, Ru-based olefin metathesis catalysts supported by dithiolate ligands. Kinetic studies elucidate marked differences in activity among the catalysts tested, with catalyst 4 providing meaningful yields of products in much shorter reaction times than stereoretentive catalysts 2 and 3. Macrocycles were generated with excellent selectivity (>99% E) and in moderate to high yields (47-80% yield) from diene starting materials bearing two E-configured olefins. A variety of rings were constructed, ranging from 12- to 18-membered macrocycles, including the antibiotic recifeiolide.

Loss and Reformation of Ruthenium Alkylidene: Connecting Olefin Metathesis, Catalyst Deactivation, Regeneration, and Isomerization.

Ruthenium-based olefin metathesis catalysts are used in laboratory-scale organic synthesis across chemistry, largely thanks to their ease of handling and functional group tolerance. In spite of this robustness, these catalysts readily decompose, via little-understood pathways, to species that promote double-bond migration (isomerization) in both the 1-alkene reagents and the internal-alkene products. We have studied, using density functional theory (DFT), the reactivity of the Hoveyda-Grubbs second-generation catalyst 2 with allylbenzene, and discovered a facile new decomposition pathway. In this pathway, the alkylidene ligand is lost, via ring expansion of the metallacyclobutane intermediate, leading to the spin-triplet 12-electron complex (SIMes)RuCl2 (3R21, SIMes = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene). DFT calculations predict 3R21 to be a very active alkene isomerization initiator, either operating as a catalyst itself, via a η3-allyl mechanism, or, after spin inversion to give R21 and formation of a cyclometalated Ru-hydride complex, via a hydride mechanism. The calculations also suggest that the alkylidene-free ruthenium complexes may regenerate alkylidene via dinuclear ruthenium activation of alkene. The predicted capacity to initiate isomerization is confirmed in catalytic tests using p-cymene-stabilized R21 (5), which promotes isomerization in particular under conditions favoring dissociation of p-cymene and disfavoring formation of aggregates of 5. The same qualitative trends in the relative metathesis and isomerization selectivities are observed in identical tests of 2, indicating that 5 and 2 share the same catalytic cycles for both metathesis and isomerization, consistent with the calculated reaction network covering metathesis, alkylidene loss, isomerization, and alkylidene regeneration.

Materia, Evonik end dispute

Materia has ended its dispute with Evonik Industries over the validity of a Materia patent on ruthenium-based olefin metathesis catalysts used to make plastics and specialty oleochemicals. Materia, whose patent is based on discoveries by chemistry Nobel laureate Robert H. Grubbs of Caltech, will now license a similar patent from Evonik. The license will extend until the patent expires in 2019. Materia CEO Nitin Apte says the “agreement ensures that Materia’s entire Grubbs catalyst portfolio continues to be available.” In January, a U.S. federal jury decided that Evonik’s patent, based on work by Technical University of Munich chemist Wolfgang Herrmann, took precedence and ordered Materia to pay Evonik $1.5 million plus interest and royalties. Materia lost an appeal in August.

Materia loses metathesis patent case

A federal jury has ordered technology and catalyst firm Materia to pay Evonik Industries royalties of more than $1.5 million in a dispute over the validity of a key patent covering ruthenium-based olefin metathesis catalysts used to make plastics and specialty oleochemicals. However, the jury also decided that Materia had not willfully or maliciously violated Evonik’s patent. It did not assess punitive damages. The Delaware jury’s decision may end a seven-year-old dispute covering academic patents licensed to Materia based on discoveries by Robert H. Grubbs of Caltech and other scientists. Grubbs, along with Yves Chauvin and Richard R. Schrock, shared the 2005 Nobel Prize in Chemistry for their role in the discovery of olefin metathesis. According to Evonik, an earlier ruling by the judge hearing the case denied the validity of Materia’s opposing patent. “A significant number of Materia’s metathesis catalysts and some products they make with them are now

Fast-Initiating, Ruthenium-based Catalysts for Improved Activity in Highly E-Selective Cross Metathesis.

Ruthenium-based olefin metathesis catalysts bearing dithiolate ligands have been recently employed to generate olefins with high E-selectivity (>99% E) but have been limited by low to moderate yields. In this report, 1H NMR studies reveal that a major contributing factor to this low activity is the extremely low initiation rates of these catalysts with trans olefins. Introducing a 2-isopropoxy-3-phenylbenzylidene ligand in place of the conventional 2-isopropoxybenzylidene ligand resulted in catalysts that initiate rapidly under reaction conditions. As a result, reactions were completed in significantly less time and delivered higher yields than those in previous reports while maintaining high stereoselectivity (>99% E).

Phosphine-Based Z-Selective Ruthenium Olefin Metathesis Catalysts

Whereas a number of highly Z-selective ruthenium-based olefin metathesis catalysts bearing N-heterocyclic carbene ligands have been reported in recent years, Z-selectivity has so far been difficult to achieve for phosphine-based catalysts. Guided by predictive density functional theory (DFT) calculations, we have developed phosphine-based ruthenium olefin metathesis catalysts giving 70–95% of the Z-isomer product in homocoupling of terminal alkenes such as allylbenzene, 1-octene, allyl acetate, and 2-allyloxyethanol. Starting from a moderately selective catalyst, [P(Cy)3](-S-2,4,6-Ph-C6H2)ClRu(═CH-o-OiPrC6H4) (4, Cy = cyclohexyl, iPr = isopropyl), obtained by substituting a chloride of the Hoveyda–Grubbs first-generation catalyst with 2,4,6-triphenylbenzenethiolate, we moved on to replace Cl and PCy3 by chelating, anionic phosphine ligands. Such ligands increase selectivity by limiting rotation around the P–Ru bond and by specifically directing the steric bulk of the phosphine substituents toward the sele...

Effect of the bulkiness of indenylidene moieties on the catalytic initiation and efficiency of second-generation ruthenium-based olefin metathesis catalysts

Fast initiation and high efficiency of ruthenium indenylidene catalysts induced by steric repulsion between two ligands (SIMes ligand and bulky indenylidene ligand).

Consequences of the electronic tuning of latent ruthenium-based olefin metathesis catalysts on their reactivity.

Two ruthenium olefin metathesis initiators featuring electronically modified quinoline-based chelating carbene ligands are introduced. Their reactivity in RCM and ROMP reactions was tested and the results were compared to those obtained with the parent unsubstituted compound. The studied complexes are very stable at high temperatures up to 140 °C. The placement of an electron-withdrawing functionality translates into an enhanced activity in RCM. While electronically modified precatalysts, which exist predominantly in the trans-dichloro configuration, gave mostly the RCM and a minor amount of the cycloisomerization product, the unmodified congener, which preferentially exists as its cis-dichloro isomer, shows a switched reactivity. The position of the equilibrium between the cis- and the trans-dichloro species was found to be the crucial factor governing the reactivity of the complexes.

Allyl Sulfides: Reactive Substrates for Olefin Metathesis

Allyl sulfides have gained traction in recent years as promoters for olefin metathesis. The high reactivity of allyl sulfides in olefin metathesis is remarkable, given that many sulfur-containing substrates are incompatible with ruthenium-based olefin metathesis catalysts. In stark contrast, allyl sulfides actually enhance the rate of metathesis in comparison with other alkenes, when matched with a suitable catalyst. This review examines how the high reactivity of allyl sulfides in olefin metathesis has been harnessed in diverse areas of synthesis. In the cases examined, allyl sulfides have been explicitly incorporated into substrates to promote olefin metathesis. Recent insights into catalyst considerations, applications in chemical and biochemical synthesis, and future opportunities are discussed.