Ruthenium Olefin Metathesis Catalysts Research Articles

From trials on rosuvastatin production waste valorization to development of new catalytic methods for Z → E isomerization of alkenes

A convenient method for Z → E geometry isomerization of aryl–aryl (stilbenes), alkyl–aryl, and alkyl–alkyl alkenes was developed.

Inhibition of the Decomposition Pathways of Ruthenium Olefin Metathesis Catalysts: Development of Highly Efficient Catalysts for Ethenolysis.

Ruthenium-based Hoveyda-type olefin metathesis catalysts bearing novel rigid spirocyclic alkyl amino carbenes (CAACs) have been developed. They are characterized by exceptional stability toward decomposition through β-elimination and bimolecular pathways, thus enabling unprecedented efficiency in the cross-metathesis of seed oil-derived fatty acid esters with ethylene (ethenolysis). Catalyst loading as low as 100 ppb was applied to the ethenolysis of the model substrate methyl oleate, leading to a remarkable turnover number (TON) of 2.6 million, significantly higher than previously reported (TON 340 000 at 1 ppm and 744 000 at 0.5 ppm catalyst loading). Ethenolysis of methyl esters derived from high oleic sunflower oil and rapeseed oil, readily available on an industrial scale, inexpensive, and renewable feedstocks, was for the first time effectively carried out with 0.5 ppm catalyst loading with TON as high as 964 000.

Regioselective 1,2-Hydrosilylation of N-Heterocycles Catalyzed by a Ruthenium Olefin Metathesis Catalyst

Regioselective 1,2-Hydrosilylation of N-Heterocycles Catalyzed by a Ruthenium Olefin Metathesis Catalyst

Ruthenium Olefin Metathesis Catalysts with Six-Membered Chelating Dithioacetal Ligands: Synthesis and Reactivity

Ruthenium sulfur-chelated benzylidenes possessing five-membered chelating architectures exhibiting latency and excellent thermal and photochemical activation behavior in various metathesis reactions are well known. On the other hand, six-membered sulfur-Ru-chelates (Ru–S) are much rarer. Herein, we describe a study of the synthesis, characterization, and catalytic properties of four new cis-dichlorido ruthenium dithioacetal-chelated complexes. As expected for sulfur-chelated benzylidenes, the X-ray structures of the complexes disclosed cis-dichloro configurations for all the complexes. The catalytic profiles of these complexes were systematically studied for benchmark RCM and ROMP reactions and provided findings on latency and activation based on chelating dithioacetal groups.

Olefin metathesis catalysts bearing hemilabile NHC ligands: Effect of remote torsional strain on activity

A ruthenium olefin metathesis catalyst (C1-H) bearing a novel NHC ligand tethered by a labile ethoxy-pyridyl arm was synthesized and characterized. The initiation rate, kinetics, metathesis activity, and decomposition behavior were compared with its methylated derivative (C1-Me), showing that these two catalysts vary profoundly. We demonstrate the considerable influence of remote torsional strain on the catalytic activity and decomposition behavior of this ligand class – a feature that can be exploited for related systems.

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.

Self-Supported Polymeric Ruthenium Complexes as Olefin Metathesis Catalysts in Synthesis of Heterocyclic Compounds

New ruthenium olefin metathesis catalysts containing N-heterocyclic carbene (NHC) connected by a linker tether to a benzylidene ligand were studied. Such obtained self-chelated Hoveyda–Grubbs type complexes existed in the form of an organometallic polymer but could still catalyze olefin metathesis after being dissolved in an organic solvent. Although these polymeric catalysts exhibited a slightly lower activity compared to structurally related nonpolymeric catalysts, they were successfully used in a number of ring-closing metathesis reactions leading to a variety of heterocyclic compounds, including biologically and pharmacologically related analogues of cathepsin K inhibitor and sildenafil (Viagra™). In the last case, a good solubility of a polymeric catalyst in toluene allowed the separation of the product from the catalyst via simple filtration.

Synthesis and catalytic olefin metathesis activity of amberlyst-15 supported cyclic and bicyclic alkyl amino carbene ruthenium complexes

Amberlyst-15 supported cyclic alkyl amino carbene and bicyclic alkyl amino carbene ruthenium olefin metathesis catalysts for sustainable catalytic applications have been synthesized by the well-known wet impregnation method utilizing ionic complex/support interaction. Surface coverages are as high as 4 and 7 wt% were achieved in the case of the significantly higher pore volume Amberlyst-15, compared to Amberlyst-36. These phase separable catalysts show high activity in cross metathesis, ring closing metathesis and ethenolysis reactions compared to the reported heterogenized olefin metathesis catalysts. Leeching tests revealed no more than 1.5 ppm ruthenium content for the investigated metathesis reactions, which is well below the accepted 10 ppm limit in case of consumer products.

Ruthenium olefin metathesis catalysts bearing two bulky and unsymmetrical NHC ligands

The activity profile of the new indenylidene complexes containing two unsymmetrical N‐heterocyclic carbene (NHC) ligands was investigated. They turned out to be effective in both straightforward olefin metathesis reactions, such as ring‐closing metathesis (RCM) of diethyl diallylmalonate, as well as in more demanding processes, such as RCM of 2,2‐di‐(2‐methylallyl)tosylate leading to a product bearing a tetrasubstituted double bond, and in selective ethenolysis of methyl and ethyl oleate.

Ruthenium Olefin Metathesis Catalysts Bearing a Macrocyclic N-Heterocyclic Carbene Ligand: Improved Stability and Activity.

Formation of sterically hindered C−C double bonds via catalytic olefin metathesis is considered a very challenging task for Ru catalysts. This limitation led to the development of specialised catalysts bearing sterically reduced N‐heterocyclic carbene (NHC) ligands that are very active in such transformations, yet significantly less stable as compared to general purpose catalysts. To decrease the small‐size NHC catalysts susceptibility to decomposition, a new NHC ligand was designed, in which two sterically reduced aryl arms were tied together by a C‐8 alkyl chain. The installation of this macrocyclic ligand on the ruthenium centre led to the formation of an olefin metathesis catalyst (trans‐Ru6). Interestingly, this complex undergoes transformation into an isomer bearing two Cl ligands in the cis‐arrangement (cis‐Ru6). These two isomeric complexes exhibit similarly high thermodynamic stability, yet different application profiles in catalysis.

Ruthenium Olefin Metathesis Catalysts Bearing a Macrocyclic N‐Heterocyclic Carbene Ligand: Improved Stability and Activity

AbstractFormation of sterically hindered C−C double bonds via catalytic olefin metathesis is considered a very challenging task for Ru catalysts. This limitation led to the development of specialised catalysts bearing sterically reduced N‐heterocyclic carbene (NHC) ligands that are very active in such transformations, yet significantly less stable as compared to general purpose catalysts. To decrease the small‐size NHC catalysts susceptibility to decomposition, a new NHC ligand was designed, in which two sterically reduced aryl arms were tied together by a C‐8 alkyl chain. The installation of this macrocyclic ligand on the ruthenium centre led to the formation of an olefin metathesis catalyst (trans‐Ru6). Interestingly, this complex undergoes transformation into an isomer bearing two Cl ligands in the cis‐arrangement (cis‐Ru6). These two isomeric complexes exhibit similarly high thermodynamic stability, yet different application profiles in catalysis.

The Janus face of high trans-effect carbenes in olefin metathesis: gateway to both productivity and decomposition.

Ruthenium–cyclic(alkyl)(amino)carbene (CAAC) catalysts, used at ppm levels, can enable dramatically higher productivities in olefin metathesis than their N-heterocyclic carbene (NHC) predecessors. A key reason is the reduced susceptibility of the metallacyclobutane (MCB) intermediate to decomposition via β-H elimination. The factors responsible for promoting or inhibiting β-H elimination are explored via density functional theory (DFT) calculations, in metathesis of ethylene or styrene (a representative 1-olefin) by Ru–CAAC and Ru–NHC catalysts. Natural bond orbital analysis of the frontier orbitals confirms the greater strength of the orbital interactions for the CAAC species, and the consequent increase in the carbene trans influence and trans effect. The higher trans effect of the CAAC ligands inhibits β-H elimination by destabilizing the transition state (TS) for decomposition, in which an agostic MCB Cβ–H bond is positioned trans to the carbene. Unproductive cycling with ethylene is also curbed, because ethylene is trans to the carbene ligand in the square pyramidal TS for ethylene metathesis. In contrast, metathesis of styrene proceeds via a ‘late’ TS with approximately trigonal bipyramidal geometry, in which carbene trans effects are reduced. Importantly, however, the positive impact of a strong trans-effect ligand in limiting β-H elimination is offset by its potent accelerating effect on bimolecular coupling, a major competing means of catalyst decomposition. These two decomposition pathways, known for decades to limit productivity in olefin metathesis, are revealed as distinct, antinomic, responses to a single underlying phenomenon. Reconciling these opposing effects emerges as a clear priority for design of robust, high-performing catalysts.

Synthesis of highly stable dual-site immobilized ruthenium olefin metathesis catalyst without ru leaching

The tri-block copolymer is used as a carrier to simultaneously immobilize the N-heterocyclic and benzylidene ligands precursor of the Ru-based catalyst to form a dual-site immobilized catalyst. The dual-site immobilized catalyst can catalyze ring-opening metathesis polymerization, ring-closing metathesis and self-metathesis. The dual-site immobilized catalyst shows good heterogeneity in dichloromethane, which simplifies the purification of product and recovery of catalyst. The dual-site immobilized catalyst exhibits excellent activity and recycling performance. The excellent recyclability can be attributed to the capture of ruthenium by the excess ligands precursor on carrier. Importantly, ruthenium residues are not detected in product.

Ruthenium Olefin Metathesis Catalysts Featuring N-Heterocyclic Carbene Ligands Tagged with Isonicotinic and 4-(Dimethylamino)benzoic Acid Rests: Evaluation of a Modular Synthetic Strategy.

A modular and flexible strategy towards the synthesis of N-heterocyclic carbene (NHC) ligands bearing Brønsted base tags has been proposed and then adopted in the preparation of two tagged NHC ligands bearing rests of isonicotinic and 4-(dimethylamino)benzoic acids. Such tagged NHC ligands represent an attractive starting point for the synthesis of olefin metathesis ruthenium catalysts tagged in non-dissociating ligands. The influence of the Brønsted basic tags on the activity of such obtained olefin metathesis catalysts has been studied.

Ruthenium Complexes Featuring Unsymmetrical N-Heterocyclic Carbene Ligands-Useful Olefin Metathesis Catalysts for Special Tasks.

This review describes a distinct class of ruthenium olefin metathesis catalysts featuring unsymmetrical N-heterocyclic carbene (uNHC) ligands, from its historical beginning to the present state of the art. Thanks to advantageous traits, such as pronounced thermodynamic stability, chemical latency, outstanding selectivity, and compatibility with green solvents, these catalysts led to good results in a number of specialized metathesis transformations. Therefore, while being a niche, the uNHC complexes can potentially be implemented in a number of industrial processes, such as valorization of Fischer-Tropsch olefin fractions, ethenolysis of renewable products, and modern pharmaceutical production.

Synthesis of Conjugated Copolymer Containing Spirobifluorene Skeleton by Acyclic Diene Metathesis Polymerization for Polymer Light‐Emitting Diode Applications

Grubbs‐type, Hoveyda‐type, cyclic alkyl amino carbene (CAAC)‐based ruthenium olefin metathesis catalysts were used for the acyclic diene metathesis (ADMET) polymerization of 2,7‐divinyl‐9,9‐di‐n‐octylfluorene (DVF). Additionally, various ratios of DVF and 2,2′,7,7′‐tetravinyl‐9,9′‐spirobifluorene (TVSF) were subjected to ADMET polymerization to obtain polymers P1–P7. Polymers P1–P4 were analyzed with gel permeation chromatography, UV–vis spectroscopy, and photoluminescence spectroscopy. As the TVSF ratio increases, polymers exhibit lower solubility but a narrower band in the photoluminescence spectrum. Polymer light‐emitting diode (PLED) devices were fabricated with polymers P1, P2, and P3. The performances of the PLED devices indicated that polymers including more spirobifluorene blocks showed better turn‐on voltage, brightness, current efficiency, and power efficiency.

Functionalization of Ruthenium Olefin-Metathesis Catalysts for Interdisciplinary Studies in Chemistry and Biology

Hoveyda–Grubbs-type complexes, ruthenium catalysts for olefin metathesis, have gained increased interest as a research target in the interdisciplinary research fields of chemistry and biology because of their high functional group selectivity in olefin metathesis reactions and stabilities in aqueous media. This review article introduces the application of designed Hoveyda–Grubbs-type complexes for bio-relevant studies including the construction of hybrid olefin metathesis biocatalysts and the development of in-vivo olefin metathesis reactions. As a noticeable issue in the employment of Hoveyda–Grubbs-type complexes in aqueous media, the influence of water on the catalytic activities of the complexes and strategies to overcome the problems resulting from the water effects are also discussed. In connection to the structural effects of protein structures on the reactivities of Hoveyda–Grubbs-type complexes included in the protein, the regulation of metathesis activities through second-coordination sphere effect is presented, demonstrating that the reactivities of Hoveyda–Grubbs-type complexes are controllable by the structural modification of the complexes at outer-sphere parts. Finally, as a new-type reaction based on the ruthenium-olefin specific interaction, a recent finding on the ruthenium complex transfer reaction between Hoveyda–Grubbs-type complexes and biomolecules is introduced.

The Impact of Water on Ru-Catalyzed Olefin Metathesis: Potent Deactivating Effects Even at Low Water Concentrations.

Ruthenium catalysts for olefin metathesis are widely viewed as water-tolerant. Evidence is presented, however, that even low concentrations of water cause catalyst decomposition, severely degrading yields. Of 11 catalysts studied, fast-initiating examples (e.g., the Grela catalyst RuCl2(H2IMes)(=CHC6H4-2-OiPr-5-NO2) were most affected. Maximum water tolerance was exhibited by slowly initiating iodide and cyclic (alkyl)(amino)carbene (CAAC) derivatives. Computational investigations indicated that hydrogen bonding of water to substrate can also play a role, by retarding cyclization relative to decomposition. These results have important implications for olefin metathesis in organic media, where water is a ubiquitous contaminant, and for aqueous metathesis, which currently requires superstoichiometric “catalyst” for demanding reactions.

Sterically Tuned N-Heterocyclic Carbene Ligands for the Efficient Formation of Hindered Products in Ru-Catalyzed Olefin Metathesis.

Formation of tetrasubstituted C–C double bonds via olefin metathesis is considered very challenging for classical Ru-based complexes. In the hope to improve this condition, three ruthenium olefin metathesis catalysts bearing sterically reduced N-heterocyclic carbene (NHC) ligands with xylyl “arms” were synthesized, characterized using both computational and experimental techniques, and tested in a number of challenging reactions. The catalysts are predicted to initiate much faster than the analogue with mesityl N-substituents. We also foreboded the rotation of xylyl side groups at ambient temperature and the existence of all four atropoisomers in the solution, which was in agreement with experimental data. These catalysts exhibited high activity at relatively low temperatures (45–60 °C) and at reduced catalyst loadings in various reactions of sterically hindered alkenes, including complex polyfunctional substrates of pharmaceutical interest, such as yangonin precursors, chrysantemic acid derivatives, analogues of cannabinoid agonists, α-terpineol, and finally a thermally unstable peroxide.

Decomposition of Ruthenium Olefin Metathesis Catalyst

Ruthenium olefin metathesis catalysts are one of the most commonly used class of catalysts. There are multiple reviews on their uses in various branches of chemistry and other sciences but a detailed review of their decomposition is missing, despite a large number of recent and important advances in this field. In particular, in the last five years several new mechanism of decomposition, both olefin-driven as well as induced by external agents, have been suggested and used to explain differences in the decomposition rates and the metathesis activities of both standard, N-heterocyclic carbene-based systems and the recently developed cyclic alkyl amino carbene-containing complexes. Here we present a review which explores the last 30 years of the decomposition studied on ruthenium olefin metathesis catalyst driven by both intrinsic features of such catalysts as well as external chemicals.