Grubbs 2nd Generation Catalyst Research Articles

Synthesis of dendronized PAMAM grafted ROMP polymers

Oxanorbornene cored 0.5, 1.5 and 2.5 generation ester terminated PAMAM dendronized monomers with 2 and 6 carbon-containing alkyl spacer in the middle of oxanorbornene core and dendronized branching were synthesized. Monomers were polymerized through the ring-opening metathesis polymerization (ROMP) technique by using 2nd and 3rd generation Grubbs catalysts to get dendronized ROMP polymers. It was found that Grubbs 3rd generation catalyst works well for 0.5 generation dendronized ROMP polymer whereas Grubbs 2nd generation catalyst works for the higher generation. We also found the linker effect during polymerization as six-carbon linker monomers polymerize with high yield along with higher generation. Finally, dendronized ROMP-based PAMAM encapsulated zero valent Cu nanoparticle was synthesized by using a reducing agent, NaBH4. The catalytic activity of this nanoparticle was further investigated from the reduction of 4-nitrophenol to 4-aminophenol.

Synthesis of styrene-norbornene diblock copolymers via ring-opening metathesis polymerization and nitroxide-mediated radical polymerization

Diblock copolymers containing polynorbornene (PNB) and polystyrene (PS) were synthesized by ring-opening metathesis polymerization (ROMP) and nitroxide-mediated radical polymerization (NMRP) approach. PNB containing nitroxide free radical was prepared by ROMP in presence of Grubbs 2nd generation catalyst and served as a macro-initiator for NMRP of styrene to achieve the targeting diblock copolymers. The effects of the chain transfer agent (CTA) concentration, catalyst amount, reaction time and reaction temperature on the synthesis of macro-initiator as well as the effects of mole ratio of monomer to macro-initiator and reaction time on the synthesis of diblock copolymers were studied. As a result, the diblock copolymers with Mn ranging from 5 kDa to 10 kDa and PDI ranging from 1.5 to 1.8 were obtained successfully. The desired diblock copolymers have broad applications in polymer electrolytes, nanoporous membranes and many other fields.

Encapsulation of the Hoveyda–Grubbs 2nd generation catalyst in magnetically separable alginate/mesoporous carbon beads for olefin metathesis reactions in water

A magnetically separable catalyst is developed through encapsulation of mesoporous carbon, HG2 and γ-Fe2O3within alginate gels. The catalytic showed superior performance in metathesis reactions of hydrophobic olefins in water under air atmosphere.

1H NMR Analysis of the Metathesis Reaction between 1-Hexene and (E)-Anethole Using Grubbs 2nd Generation Catalyst: Effect of Reaction Conditions on (E)-1-(4-Methoxyphenyl)-1-hexene Formation and Decomposition

The metathesis of 1-hexene and (E)-anethole in the presence of Grubbs 2nd generation catalyst was monitored by in situ 1H NMR spectroscopy at different temperatures (15 °C, 25 °C, and 45 °C) and anethole mol fractions (XAnethole ≈ 0.17, 0.29, 0.5, 0.71, 0.83). Time traces confirmed the instantaneous formation of (E)-1-(4-methoxyphenyl)-1-hexene, the cross-metathesis product. A maximum concentration of (E)-1-(4-methoxyphenyl)-1-hexene is reached fairly fast (the time depending on the reaction conditions), and this is followed by a decrease in the concentration of (E)-1-(4-methoxyphenyl)-1-hexene due to secondary metathesis. The maximum concentration of (E)-1-(4-methoxyphenyl)-1-hexene was more dependent on the XAnethole than the temperature. The highest TOF (3.46 min−1) was obtained for the reaction where XAnethole was 0.16 at 45 °C. The highest concentration of the cross-metathesis product was however achieved after 6 min with an anethole mol fraction of 0.84 at 25 °C. A preliminary kinetic study indicated that the secondary metathesis reaction followed first order kinetics.

Synthesis and characterization of natural rubber‐based telechelic oligomers via olefin metathesis

AbstractMetathesis degradation and functionalization of natural rubber (NR) were conducted with 1‐hexene, 1‐octene, 1‐decene, 1‐dodecene, trans‐stilbene, and 4,4′‐dibromo‐trans‐stilbene as chain transfer agents (CTAs) in presence of Grubbs 2nd generation catalyst to generate NR‐based telechelic oligomers that had been a long‐lasting challenge due to the structure and compositions of NR with various impurities. Orthogonal experiments were applied and the effects of the CTA type, CTA concentration, catalyst concentration, reaction time, and reaction temperature on the formation of telechelic oligomers were studied, indicating that the catalyst concentration was the major factor influencing the number average molecular weights (Mn) and polymer dispersity index (PDI) of telechelic oligomers. The structures of the oligomers were characterized using 1H NMR, 13C NMR, and MALDI‐TOF‐MS, which confirmed the formation of the designed terminal groups. The results showed that well‐defined telechelic oligomers with a Mn of a few thousand and a PDI around 1.6 were obtained, with potential applications in binder, lubricant and many other fields.

Spectroscopic characterisation of Grubbs 2nd generation catalyst and its p-cresol derivatives

p-Cresol derivatives of the Grubbs 2nd generation catalyst were prepared with either hydrogen bonds between p-cresol and the Cl-ligands or ligand exchange between the Grubbs 2nd generation catalyst and thallium p-cresolate to form Ru-O coordination bonds and TlCl. ATR FTIR and UV–Vis spectroscopic studies revealed a blue shift in certain bands, indicating that coordination occurred. X-ray Photoelectron Spectroscopy was recorded for each of the three Ru-complexes. The binding energy of the Ru 3d5/2, Ru 3p3/2 photoelectron line (found at ca. 281 and 462 eV, respectively) of the different complexes showed the influence of the inductive electronic effects of the p-cresol interaction with the complexes. The Cl 2p photoelectron lines indicated ionic and covalent environments, representing the TlCl and the Ru-Cl bonds, respectively. The atomic ratio between Ru:P:Cl:N:Tl confirmed the binding modes of p-cresol to the Grubbs 2nd generation catalyst.

Acrylate Esters by Ethenolysis of Maleate Esters with Ru Metathesis Catalysts: an HTE and a Technoeconomic Study

AbstractA high throughput experimentation (HTE) study identified active Ru metathesis catalysts and reaction conditions for the ethenolysis of maleate esters to the respective acrylate esters. Catalysts were tested at various loadings (75–10’000 ppm) and temperatures (30–60 °C) with maleate esters dissolved in toluene (up to ca. 44 wt‐%) or neat and at variable partial pressures of ethylene (0.2–10 bar). Ruthenium catalysts containing a PCy3 ligand, such as 1st or 2nd generation Grubbs catalysts, as well as the state‐of‐the‐art catalysts containing cyclic alkyl amino carbene (CAAC) ligands, are generally inferior to Hoveyda–Grubbs 2nd generation catalyst in ethenolysis of maleates. Productive turnover numbers could exceed 1900 if the ethenolysis reaction is performed at low ethylene pressure (0.2–3 bar) and reach 5200 when a polymeric phenol additive was used. Such catalytic performance falls well within the window practiced in industry. Moreover, a crude technoeconomic analysis finds similar production cost for the ethenolysis route and conventional technology, that is, propene oxidation followed by esterification, justifying research to further improve the ethenolysis route.

Synthesis and Gas Permeability of Chemically Cross‐Linked Polynorbornene Dicarboximides Bearing Fluorinated Moieties

AbstractThis work reports on the synthesis of a novel bifunctional norbornene dicarboximide monomer (HFDA) based on 4,4′‐(hexafluoroisopropylidene)bis(p‐phenyleneoxy)dianiline and its application as a cross‐linking agent in the ring‐opening metathesis polymerization (ROMP) with N‐3‐trifluoromethylphenyl‐exo,endo‐norbornene‐5,6‐dicarboximide (mCF3) employing the Grubbs 2nd generation catalyst (I) and cis‐1,4‐diacetoxy‐2‐butene as a chain transfer agent (CTA) to yield a series of soluble nonlinear highly branched chains polymers with increasing degree of cross‐linking. A comparative study of gas transport in membranes based on these cross‐linked polynorbornene dicarboximides is performed and the gases studied are hydrogen, oxygen, nitrogen, carbon dioxide, methane, ethylene, and propylene. It is found that cross‐linking increases the gas permeability, leads to the highest separation factor reported to date for the H2/C3H6 mixture in this kind of polymers, and also enhances the CO2 plasticization resistance up to 14 atm upstream pressure. The chemical cross‐linking approach employed in this research is an effective tool to enhance gas transport properties for dense polynorbornene dicarboximide membranes.

Dewar lactone as a modular platform to a new class of substituted poly(acetylene)s

A variety of 3-substituted-4-halocyclobutenes originating from Dewar lactone (2-oxabicyclo[2.2.0]hex-5-en-3-one) were synthesized and polymerized using the Hoveyda–Grubbs 2nd generation catalyst.

ChemInform Abstract: New Metathesis Catalyst Bearing Chromanyl Moieties at the N‐Heterocyclic Carbene Ligand.

AbstractA new type of Hoveyda—Grubbs 2nd generation catalyst bearing a modified N‐heterocyclic carbene ligand with chromanyl moieties is synthesized.

New metathesis catalyst bearing chromanyl moieties at the N-heterocyclic carbene ligand.

The synthesis of a new type of Hoveyda–Grubbs 2nd generation catalyst bearing a modified N-heterocyclic carbene ligands is reported. The new catalyst contains an NHC ligand symmetrically substituted with chromanyl moieties. The complex was tested in model CM and RCM reactions. It showed very high activity in CM reactions with electron-deficient α,β-unsaturated compounds even at 0 °C. It was also examined in more demanding systems such as conjugated dienes and polyenes. The catalyst is stable, storable and easy to purify.

Computational study of productive and non-productive cycles in fluoroalkene metathesis.

A detailed DFT study of the mechanism of metathesis of fluoroethene, 1-fluoroethene, 1,1-difluoroethene, cis- and trans-1,2-difluoroethene, tetrafluoroethene and chlorotrifluoroethene catalysed with the Hoveyda–Grubbs 2nd generation catalyst was performed. It revealed that a successful metathesis of hydrofluoroethenes is hampered by a high preference for a non-productive catalytic cycle proceeding through a ruthenacyclobutane intermediate bearing fluorines in positions 2 and 4. Moreover, the calculations showed that the cross-metathesis of perfluoro- or perhaloalkenes should be a feasible process and that the metathesis is not very sensitive to stereochemical issues.

Synthesis of amide-functionalized cellulose esters by olefin cross-metathesis

Cellulose esters with amide functionalities were synthesized by cross-metathesis (CM) reaction of terminally olefinic esters with different acrylamides, catalyzed by Hoveyda–Grubbs 2nd generation catalyst. Chelation by amides of the catalyst ruthenium center caused low conversions using conventional solvents. The effects of both solvent and structure of acrylamide on reaction conversion were investigated. While the inherent tendency of acrylamides to chelate Ru is governed by the acrylamide N-substituents, employing acetic acid as a solvent significantly improved the conversion of certain acrylamides, from 50% to up to 99%. Homogeneous hydrogenation using p-toluenesulfonyl hydrazide successfully eliminated the α,β-unsaturation of the CM products to give stable amide-functionalized cellulose esters. The amide-functionalized product showed higher Tg than its starting terminally olefinic counterpart, which may have resulted from strong hydrogen bonding interactions of the amide functional groups.

ChemInform Abstract: Synthesis and Reactivity of Oxygen Chelated Ruthenium Carbene Metathesis Catalysts.

AbstractSix NHC Ru complexes are prepared by etherification of 4‐substituted 2‐(propen‐1‐yl)phenols with either ethyl alpha‐bromopropionate or 2‐bromo‐gamma‐butyrolactone followed by reaction with Grubbs 2nd generation catalyst in the presence of CuCl.

ADMET Polymerization of Amino‐Acid‐Based Diene

1,4‐Di(homo)allyl‐2,5‐diketopiperazines are synthesized and polymerized via ADMET using the Hoveyda–Grubbs 2nd generation catalyst. The but‐3‐enylated diketopiperazine can be converted into unsaturated tertiary polyamide with molar mass of <3000 g mol−1, whereas the allylated diketopiperazine cannot. Double‐bond isomerization occurs regardless of whether or not benzoquinone is present. A polyesteramide with a higher molar mass of ca. 4800 g mol−1 is obtained by the alternating copolymerization (ALTMET) of 1,4‐di(but‐3‐enyl)‐2,5‐diketopiperazine and ethylene glycol diacrylate. A post‐polymerization modification of the poly(ester)amides via radical thiol‐ene chemistry, however, fails. image

An Immobilised Grubbs 2nd Generation Catalyst for Application in Flow‐Through Devices

AbstractAn improved immobilised Grubbs 2nd generation catalyst and its application in flow‐through devices, shown for on‐column reaction gas chromatography (ocRGC), has been studied. The coupling of a reaction capillary and a separation column in GC/MS allows direct reaction monitoring and analysis of conversion as well as reaction kinetics. The presented permanently bonded N‐heterocyclic carbene ligand shows a great stability and activity in ring closing metathesis reactions. A salt‐free approach was used to generate the carbene ligand, which can be directly monitored by mass spectrometry. The very flexible design of the immobilised ligand system in reaction channels and capillaries of flow through systems allows the preparation of various catalysts using a broad variety of metal precursors. This strategy of immobilised catalytically active complexes offers a wide range of on‐column reactions combinable with fast reaction screening by high throughput experimentation.magnified image

Triacylglycerol self-metathesis over highly chemoselective methyltrioxorhenium supported on ZnCl2-promoted mesoporous alumina

Since triolein is the main constituent of most oils such as olive and high oleic sunflower oils, self-metathesis of this triacylglycerol at mild reaction conditions was investigated via a heterogeneous approach, in the presence of ZnCl2-modified mesoporous alumina supported methyltrioxorhenium (MTO) as a catalyst. Both intra and intermolecular metathesis reactions were observed. While, 9-octadecene, dimers and trimers of the triacylglycerol were isolated, intermolecular cyclization metathesis products were also obtained. The MTO-based catalyst was found to be highly chemoselective affording only desired metathesis product formation. In contrast, more than 50% of triolein was converted to undesired solid product in the presence of the homogeneous Grubbs 2nd generation catalyst. Triolein metathesis products were effectively separated by chromatographic techniques and identified using mass spectrometric and NMR analyses. The reported results show that 3%MTO/ZnCl2–Al2O3-meso is an efficient and selective heterogeneous catalyst for bulky functionalized olefins metathesis such as triacylglycerols and edible oils, avoiding the use of costly homogeneous catalysts, or the use other rhenium-based catalysts with toxic promoters such as R4Sn.

ChemInform Abstract: Enantioselective Synthesis of Benzofurans and Benzoxazines via an Olefin Cross‐Metathesis—Intramolecular Oxo‐Michael Reaction

Abstractusing a catalytic system of Hoveyda—Grubbs 2nd generation catalyst and a chiral BINOL‐derived phosphoric acid

Experimental and theoretical study of Hoveyda–Grubbs catalysts modified by perfluorohexyl ponytail in the alkoxybenzylidene ligand

The alkoxybenzylidene ligand of Hoveyda–Grubbs 1st and 2nd generation catalysts was modified with one or two perfluorohexyl groups by Ullmann reaction with the aim to improve both the fluorophilicity and activity of the catalyst. While bis(perfluorohexylation) resulted in inability of the ligand to exchange tricyclohexylphosphine ligand of parent Grubbs catalysts, mono(perfluorohexylation) and subsequent ligand exchange resulted in the formation of complexes of light fluorous properties and substantially higher activity in model RCM reactions. Modification of the mesityl group of the unsaturated NHC ligand by polyfluoroalkyl ponytails resulted in the formation of ruthenium precatalyst furnishing active catalytic intermediate with light fluorous properties. DFT computations of the model initiation reaction of ethene with Hoveyda–Grubbs 2nd generation catalyst or its pentafluoroethylated counterpart revealed that in the latter, the intermediate ruthenacyclobutane can form and decompose with significantly lower energies, thus explaining its higher activity.

Insertion metathesis depolymerization

We have successfully depolymerized polybutadiene via an insertion metathesis mechanism. This new concept involves the irreversible depolymerization of unsaturated polymers with electron deficient olefins. The product of the degradation was characterized by NMR and GC-MS. We also explored the use of copper iodide as an additive. We observed significant reduction of molecular weight under a variety of conditions with the most extensive depolymerization occurring with the use of Grubbs 2nd generation catalyst with CuI. Finally, polybutadiene was converted to a polyamide by performing insertion metathesis depolymerization with acryloyl chloride and subsequently reacting with 1,6-diaminohexane, demonstrating the potential of polymer-to-polymer conversions with this chemistry.