Grubbs Catalyst 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.

Cross-Linked Metathesis Polynorbornenes Based on Nadimides Bearing Hydrocarbon Substituents: Synthesis and Physicochemical Properties.

Metathesis homo- and copolymerization of bifunctional monomers bearing two norbornene moieties was studied. The monomers were synthesized from cis-5-norbornene-exo-2,3-dicarboxylic anhydride and various diamines (hexamethylenediamine, decamethylenediamine, 1R,3S-isophoronediamine). The metathesis homopolymerization of these bis(nadimides) in the presence of the second-generation Grubbs catalyst afforded glassy cross-linked polymers in more than 90% yields. The metathesis copolymerization of the bis(nadimides) and a monofunctional norbornene derivative containing the β-pinene fragment also resulted in insoluble cross-linked polymers in nearly quantitative yields. The structures and purity of the synthesized polymers were confirmed via IR spectroscopy and CP/MAS NMR spectroscopy. Conditions for the fabrication of mechanically strong solution-cast thin films based on copolymers synthesized from the comonomers mentioned above were determined by varying the content of the cross-linking agent. It was shown that the films made in this way are stable in a range of organic solvents and could be useful as semipermeable or membrane materials for use in liquid organic media. The permeability of the polymer films in question to 1-phenylethanol and mandelic acid was studied. The results obtained are discussed along with the data from the DSC, TGA, and powder X-ray diffraction studies of the properties of the synthesized metathesis homo- and copolymers.

Impact of the Olefin and Diazene Structure on the Heterofunctional Azo Metathesis Catalyzed by the First-Generation Grubbs Catalyst

Impact of the Olefin and Diazene Structure on the Heterofunctional Azo Metathesis Catalyzed by the First-Generation Grubbs Catalyst

High Molecular Weight Semicrystalline Substituted Polycyclohexene From Alternating Copolymerization of Butadiene and Methacrylate and Its Ambient Depolymerization.

Cyclohexene cannot be polymerized via ring-opening polymerization under any conditions due to its lack of ring strain. A hypothetical polycyclohexene would therefore have a strong thermodynamic driving force to depolymerize to monomer if a metathesis catalyst were provided while otherwise having thermal and hydrolytic stability under normal conditions because of its hydrocarbon backbone. We envisioned access to this otherwise unattainable family of polymers via the alternating polymerization of a diene and an alkene. Ethyl aluminum chloride was found to promote highly alternating polymerization of butadiene and methacrylate when radically initiated at room temperature, resulting in formal polycyclohexene structures. Ultrahigh molecular weight (up to 1750 kDa) polymers can be synthesized at the decagram scale in high monomer conversions. The resulting presumably atactic copolymers exhibited semicrystallinity, leading to high toughness. In the presence of a small amount of the Grubbs catalyst, the generated polycyclohexene can be fully depolymerized at ambient temperatures into pure constituent cyclohexene. The strategy of using orthogonal chemistry for the polymerization and depolymerization processes allows access to polymer structures with subambient ceiling temperatures without using ultralow temperature synthesis or relying on the monomer-polymer equilibrium.

Anionic Olefin Metathesis Catalysts Enable Modification of Unprotected Biomolecules in Water.

Stability problems have limited the uptake of cationic olefin metathesis catalysts in chemical biology. Described herein are anionic catalysts that improve water-solubility, robustness, and compatibility with biomolecules such as DNA. A sulfonate tag is installed on the cyclic (alkyl)(amino) carbene (CAAC) ligand platform, chosen for resistance to degradation by nucleophiles, base, water, and β-elimination. Hoveyda-Grubbs catalysts bearing the sulfonated CAAC ligands deliver record productivity in metathesis of unprotected carbohydrates and nucleosides at neutral pH. Decomposed catalyst has negligible impact on metathesis selectivity, whereas N-heterocyclic carbene (NHC) catalysts degrade rapidly in water and cause extensive C=C migration.

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 catalyts such as StickyCat,TM AquaMetTM and GreenCatTM. 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.

Tailoring the Structure-Property Relationship of Ring-Opened Metathesis Copolymers for CO2-Selective Membranes.

In this work, we explore the use of ring-opening metathesis polymerization (ROMP) facilitated by a second-generation Grubbs catalyst (G2) for the development of advanced polymer membranes aimed at CO2 separation. By employing a novel copolymer blend incorporating 4,4'-oxidianiline (ODA), 1,6-hexanediamine (HDA), 1-adamantylamine (AA), and 3,6,9-trioxaundecylamine (TA), along with a CO2-selective poly(ethylene glycol)/poly(propylene glycol) copolymer (Jeffamine2003) and polydimethylsiloxane (PDMS) units, we have synthesized membranes under ambient conditions with exceptional CO2 separation capabilities. The strategic inclusion of PDMS, up to a 20% composition within the PEG/PPG matrix, has resulted in copolymer membranes that not only surpass the 2008 upper limit for CO2/N2 separation but also meet the commercial targets for CO2/H2 separation. Comprehensive analysis reveals that these membranes adhere to the mixing rule and exhibit percolation behavior across the entire range of compositions (0-100%), maintaining robust antiplasticization performance even under pressures up to 20 atm. Our findings underscore the potential of ROMP in creating precisely engineered membranes for efficient CO2 separation, paving the way for their application in large-scale environmental and industrial processes.

Improved interfacial adhesion of carbon fiber‐reinforced polydicyclopentadiene layered composite material by modification of norbornene derivatives

AbstractSurface chemical grafting modifications of carbon fibers (CFs) using 5‐(triethoxysilyl)norbornene (TOS), norbornene carboxylic acid tert‐butyl ester (NB‐TBE), and 5‐norbornene‐2,3‐dicarboxylic anhydride (NA) improved interfacial interactions between CFs and poly(dicyclopentadiene) (PDCPD) resin. The ring‐opening metathesis polymerization (ROMP) of DCPD, catalyzed by Grubbs catalyst II, enabled the fabrication of PDCPD/CF layered composite materials with resin and fibers tightly adhered. The optimal composite exhibited remarkable mechanical properties, with a tensile strength of 654.6 MPa and flexural strength of 510.7 MPa. Excellent thermal stability with a maximum weight loss rate in temperatures above 450°C and good chemical resistance with a weight change of about 1% in both acidic and alkaline media highlight the promising potential of these materials for use in harsh environments. The simple yet efficient approach of TOS, NB‐TBE, and NA‐enhanced layered CF shows great promise as advanced composite materials for industrial applications.Highlights Norbornene derivatives such as TOS, NB‐TBE, and NA are suitable modifiers for CF. ROMP of DCPD and norbornene group onto CFs, fabrication of PDCPD/CF composite materials. The composite exhibited remarkable interfacial adhesion and mechanical properties.

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.

Ring Opening Metathesis Polymerization of Cyclooctadiene and Cyclooctene with Dihydrofuran: Influence of Ru Fischer Carbene.

Vinyl ethers are commonly used to deactivate Grubbs catalysts and terminate ring opening metathesis polymerization (ROMP) by forming Fischer carbene species with attenuated metathesis reactivity. However, we recently demonstrated that a cyclic enol ether, 2,3-dihydrofuran (DHF), can in fact be homopolymerized or copolymerized with norbornene derivatives. 1,5-Cyclooctadiene (COD) and cyclooctene (COE) consist of an important class of ROMP monomers, and we describe here a study of their copolymerization with DHF. Addition of DHF greatly suppressed the ROMP activity of COD and COE and resulted in significant alkene isomerization of COD. Chloranil was found to be an effective additive to prevent undesired isomerization and promote copolymerization. As a result, high molecular weight COD/COE and DHF copolymers were synthesized. Hydrolysis of the enol ether main chain linkages yields polyalkenamers with alcohol and aldehyde end groups. This study encourages further exploration of the in situ formed Ru Fischer carbene species in ROMP to access degradable polymers.

Selective synthesis of α-vinyl-ω-vinylidene-oligoisoprene as a macromonomer via ethenolysis of polyisoprene

Oligoisoprene macromonomer, which bears a terminal vinyl group, was prepared by the metathesis degradation of high-molecular-weight polyisoprene with ethylene for coordination polymerization. The ethenolysis of polyisoprene using the 2nd-generation Grubbs catalyst (G2) at ambient pressure gave heterotelechelic (α-vinyl-ω-vinylidene) oligoisoprene, keeping the stereoregularity in high yield, whereas the 1st generation Grubbs catalyst was immediately deactivated. In such metathesis degradation, an intramolecular side reaction giving cyclic oligomers may be competitive, but ethenolysis proceeded with high selectivity, probably because of the least steric effect of ethylene. The ethenolysis is also applicable for the degradation of natural rubber-derived polyisoprene, although the catalytic activity decreased. The prepared oligoisoprene macromonomer was successfully copolymerized with ethylene using a phenoxyimine-ligated titanium catalyst, and the reactivity of the macromonomer was almost the same as that of 1-hexadecene. The oligoisoprene-grafted polyethylene showed a typical stress‒strain curve, of which the tensile modulus and yielding stress are comparable to those of linear low-density polyethylene.

A bioinspired bifunctional catalyst: an amphiphilic organometallic catalyst for ring-closing metathesis forming liquid droplets in aqueous media.

Inspired by phase-separated biopolymers with enzymatic activity, we developed an amphiphilic catalyst consisting of alternating hydrophilic oligo(ethylene glycol) and hydrophobic aromatic units bearing a Hoveyda-Grubbs catalyst center (MAHGII). MAHGII served as both a droplet-forming scaffold and a catalyst for ring-closing metathesis reactions, providing a new biomimetic system that promotes organic reactions in an aqueous environment.

“Metafining” of nerolidol with a Grubbs-Hoveyda catalyst to generate high-performance sustainable aviation fuels

trans-Nerolidol was converted into high-performance sustainable aviation fuel by a combination of ring-closing olefin metathesis, dehydration, and hydrogenation. The fuels exhibited exceptional gravimetic energy density and low viscosity.

Latency for All: Enabling Latency of Hoveyda-Grubbs Second-Generation Catalysts by Adding Phosphite Ligands.

The Hoveyda-Grubbs catalyst (HG2, M720 Umicore) is among the most widely used catalysts in olefin metathesis reactions. Given the usefulness of HG2 and the great interest in developing latent olefin metathesis catalysts for numerous applications, we developed a method to introduce phosphite molecules as ancillary ligands into the precatalyst framework. This modification alters the geometry of the complex from an active trans-dichloro form to a latent cis-dichloro species. Most unusually, the ligands coordinate to HG2 only in solidified solutions (most likely due to entropic factors), providing latent catalysts that can be activated on demand by heat or light by regenerating the original HG2 catalyst. Of particular interest is the use of these latent catalysts in ring-opening metathesis polymerization (ROMP) reactions and 3D printing methods. Indeed, the novel complexes displayed the required latency toward ROMP monomers, even the most reactive dicyclopentadiene. Irradiation with 405 nm light readily results in the expedited formation of the desired polymers. This novel approach provides a general and straightforward way to access efficient and well-defined latent olefin metathesis catalysts.

Evaluating Catalyst Performance in Synthesizing Hydroxyl-Terminated Polybutadiene by Ring-Opening-Metathesis Polymerization

AbstractHydroxyl-terminated polybutadiene (HTPB) can be synthesized by ring-opening metathesis polymerization (ROMP) in a one-step process using cyclooctadiene in the presence of a hydroxyl-functionalized chain-transfer agent (CTA). However, previous studies have shown that the presence of primary alcohols can lead to the degradation of some ruthenium catalysts and that the hydroxyl end groups may be converted into aldehydes. Here we compare the performance of five ruthenium-based catalysts — Grubbs first-, second-, and third-generation catalysts (G1, G2, and G3, respectively), Hoveyda–Grubbs Z-selective catalyst (HGZ), and Hoveyda–Grubbs second-generation catalyst (HG2) — in ROMP with a CTA containing primary alcohols. We found that HTPB can be rapidly synthesized in a single step using G3 while avoiding end-group isomerization (2.2% aldehyde formation after full conversion is reached in 5 min). This result suggests that G3 may enable a more effective approach to synthesizing HTPB that avoids protecting groups but still maintains high end-group fidelity.

Ring-Opening Metathesis Polymerization of the Dewar Isomer of 1,2-Azaborinine, a B-N Isostere of Benzene.

The successful polymerization of the Dewar isomer of an azaborinine heterocycle is reported. Controlled ring-opening metathesis polymerization was accomplished with Grubbs and Hoveya-Grubbs second generation catalysts (G2, HG2), as well as a Z-selective Ru catalyst (HGM2001). The structure of the polymers containing 4-membered B-N heterocycles was verified by GPC and multinuclear and 2D NMR. Differences in stereochemistry of polymers derived from G2/HG2 versus the Z-selective catalyst HGM2001 were substantiated by 2D NOESY, FT-IR, and Raman analyses. The incorporation of B-N heterocycles into these polymer structures is promising as a route to functional polymers that contain polar side groups.

Marriage of Organic and Grubbs Catalysts for Tandem Synthesis of Bottlebrush Polyesters.

Bottlebrush polymers (BBPs) have gained wide attention for their special characters, such as rigid main/side chains, stemming from the exceedingly high graft density. This study aims to provide a simple synthetic approach to BBPs with polyester side chains by merging ring-opening alternating copolymerization (ROAP) and ring-opening metathesis polymerization (ROMP). A simple phosphazene base (tBuP1) is employed for the ROAP of phthalic anhydride and epoxide, after which Grubbs third-generation catalyst (G3) is added to in situ switch on ROMP of the macromonomer, i.e., norbornenyl-ended alternating polyester. The compatibility of tBuP1 with G3 and well-controlled ROMP is evidenced by DOSY-NMR of mixed catalysts, characterization of BBPs, and side-chain degradation. The method can also be extended to BBPs with one-step synthesized block copolyesters side chains. These results highlight the strength of the non-nucleophilic organobase catalyst for convenient construction of complex (degradable) polymers with compositional diversity.

Unconventional Reactivity of a Grubbs Catalyst: Hydroalkylation Overriding Metathesis.

Unprecedented reactivity of a Grubbs catalyst has been disclosed in a reaction between vinyl azaarenes and alkenylnitriles under standard metathesis conditions. No metathesis was observed; only hydroalkylation products were obtained in high yields. The practical utility of this method has been demonstrated by the application of the products in useful transformations, e.g., the formation of cyclic iminoesters and highly challenging medium-sized carbocycles.

Furandicarboxylate Polyesters: A Comprehensive ADMET Study of a Novel Class of Furan-Based α,ω-Diene Monomers.

The present research article delves into the preparation of a new class of bio-based polyesters from α,ω-diene furandicarboxylate monomers. In particular, it exploits the use of acyclic diene metathesis polymerisation (ADMET) on 2,5-furandicarboxylic acid (FDCA)-derived compounds. First, a library of furan-based α,ω-diene monomers was prepared via acid- or base-catalyzed transesterification of 2,5-furandicarboxylic acid dimethyl ester (FDME) with commercially available alcohols incorporating terminal olefins, i. e., allyl alcohol, but-3-en-1-ol, hex-5-en-1-ol and dec-9-en-1-ol. Then, the novel monomers were subjected to ADMET polymerisation employing different catalysts and reaction conditions. Interestingly, first-generation Grubbs catalyst was found to be the best promoter for ADMET polymerisation. This catalyst allowed the preparation of a new family of bio-based polyesters with molecular weights up to 26.4 kDa, with good thermal stability, and adaptable cis-trans conformations. Results also revealed that the monomer structure had a direct impact on the polymerisation efficiency and the resulting thermal properties. The effect of green bio-based solvents such as Cyrene™, dimethyl isosorbide (DMI) and γ-valerolactone (GVL) on the polymerisation process was also studied. Data collected showed that the solvent concentration influenced both the yield and length of polymers formed. Furthermore, some co-polymerisation experiments were conducted; the successful integration of different monomers in the resulting copolymer was shown to affect the glass transition temperature (Tg) of the resulting materials.

Enhancing Thermomechanical Strength and Thermal Stability of Poly(dicyclopentadiene) Composites through Cost-Effective Fly Ash Reinforcement for Structural and Impact Applications.

Poly(dicyclopentadiene) (poly-DCPD) is a thermoset with potential for high-performance applications. In this research, epoxy resin was blended with different concentrations of fly ash class F particles at 0.0, 1.0, 10.0, and 50.0 wt.%, aiming to improve its use as a high-volume structural material by decreasing costs and reducing its negative environmental impact through using fly ash particles. A planetary Thinky mixer was used to initially mix the resin with the curing agent, followed by incorporating a Grubbs catalyst. The microstructures were analyzed using scanning electron microscopy (SEM), where particles were found to be homogeneously distributed over the polymer matrix. The thermomechanical behavior was evaluated via curing, compression, dynamic mechanical analysis (DMA), and thermo-gravimetric analysis (TGA). Nanoindentation tests were also conducted. Fly ash was found to decelerate the curing of the resin through the release of calcium ions that enhanced the exothermic reaction.