2nd Generation Catalyst Research Articles

A mini‐review of intensified synthesis of 1st and 2nd generation biofuels in the presence of perovskite catalysts

AbstractEnhancement of a sustainable environment through the choice of a selective catalyst with high activity, regeneration nature, and high stability is an important aspect to be focused on to achieve a high yield and maximum conversion of feedstock to biodiesel (1st generation biofuel), and also in the biomass valorization/pyrolysis (2nd generation biofuel synthesis). Depending on the nature of the catalyst and synthesis method adopted for biofuel production and biomass valorization, the variations in the process conditions, final yield, and conversion are varied accordingly. A prospective development and application of perovskite catalysts in the synthesis of 1st and 2nd generation biofuels using various process intensification strategies for the development of a clean and green environment is reviewed in this study. The synthesis of types of perovskite catalysts polycrystalline, nano‐sized, and powdered oxide are also discussed in this review. It is also concluded that, apart from other process parameters, molar ratio is one of the most influencing sensitive factors in the case of 1st generation biofuel synthesis, whereas during the production of 2nd generation biofuels, catalyst concentration and liquid–solid ratio are more significant process parameters that change based on the nature of the catalyst selected for the reaction.

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.

Metal-Free Ring-Opening Metathesis Polymerization with Hydrazonium Initiators.

The ring-opening metathesis polymerization (ROMP) of cyclopropenes using hydrazonium initiators is described. The initiators, which are formed by the condensation of 2,3-diazabicyclo[2.2.2]octane and an aldehyde, polymerize cyclopropene monomers by a sequence of [3+2] cycloaddition and cycloreversion reactions. This process generates short chain polyolefins (Mn ≤9.4 kg mol-1 ) with relatively low dispersities (Đ≤1.4). The optimized conditions showed efficiency comparable to that achieved with Grubbs' 2nd generation catalyst for the polymerization of 3-methyl-3-phenylcyclopropene. A positive correlation between monomer to initiator ratio and degree of polymerization was revealed through NMR spectroscopy.

Metal‐Free Ring‐Opening Metathesis Polymerization with Hydrazonium Initiators**

AbstractThe ring‐opening metathesis polymerization (ROMP) of cyclopropenes using hydrazonium initiators is described. The initiators, which are formed by the condensation of 2,3‐diazabicyclo[2.2.2]octane and an aldehyde, polymerize cyclopropene monomers by a sequence of [3+2] cycloaddition and cycloreversion reactions. This process generates short chain polyolefins (Mn≤9.4 kg mol−1) with relatively low dispersities (Đ≤1.4). The optimized conditions showed efficiency comparable to that achieved with Grubbs’ 2nd generation catalyst for the polymerization of 3‐methyl‐3‐phenylcyclopropene. A positive correlation between monomer to initiator ratio and degree of polymerization was revealed through NMR spectroscopy.

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.

Plasticizers: Synthesis of phthalate esters via FeCl3-catalyzed nucleophilic addition of alcohols to phthalic anhydride

Phthalates are esters of phthalic anhydride. Phthalic anhydride (1) has been reacted with alcohols 2 to synthesize phthalate monoesters 3 and diesters 4 with the favor of latter compound that primarily used as plasticizers worldwide. This two-steps process operates in single pot, in the presence of 10 mol% of FeCl3 as a catalyst. Mechanistically, the first step is the formation of phthalate monoesters 3 that involves a facile addition-displacement pathway, and the second step is essentially underwent a Lewis acid catalysis providing phthalate diesters 4 with very good yields. Application of the present reaction is demonstrated by synthesizing a macrolide 5 through the ring-closing metathesis of diallyl phthalate (4b) using the Grubb’s 2nd generation catalyst.

Ion-Functionalized Silver(I) Carboxylates: Synthesis and Application in Ru-Catalyzed Olefin Metathesis Reaction

The Grubbs–Hoveyda catalysts have a wide range of applications in catalyzed formation of the carbon-carbon double bonds. In this study, several imidazolium- functionalized or pyridinium-functionalized silver carboxylates have been prepared, and their reaction with Grubbs–Hoveyda 2nd generation (G–H 2nd) catalyst leads a new type of processes. Activity and selectivity of the catalysts have been preliminarily evaluated using cross olefin metathesis reactions.

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 of high-molecular weight poly(1,1-dimethyl-1-silapentene) by olefin metathesis polymerization in the presence of Grubbs catalysts

Heterochain polycarbosilanes are well-known materials possessed important properties. Some of their applications, such as gas separation membranes, require polymers with high molecular weight that provide good film-forming and mechanical properties. In this research, the synthesis of poly(1,1-dimethyl-1-silapentene) via the ring-opening metathesis polymerization (ROMP) of 1,1-dimethyl-1-silacyclopentene and the acyclic dienes metathesis (ADMET) of diallyldimethylsilane mediated by Ru-carbene Grubbs complexes 1st - 3rd generations as well as Hoveyda-Grubbs 2nd generation catalyst were studied for the first time. High molecular weight poly(1,1-dimethyl-1-silapentene) was synthesized by ROMP of 1,1-dimethyl-1-silacyclopentene. Varying the type and loading catalyst, temperature and monomer concentration, we obtained poly(1,1-dimethyl-1-silapentene) with Mw = 100–143 kDa, which is significantly higher (5–7 times) than that reached previously by olefin metathesis polymerization. The activities of 1,1-dimethyl-1-silacyclopentene and cyclopentene in ROMP were compared using 1H NMR monitoring the conversion of their double bonds. The ADMET polymerization of diallyldimethylsilane led to oligomers with the average polymerization degree not exceeded 4.4.

Ligand Substitution of RuII -Alkylidenes to Ru(bpy)3 2+ : Sequential Olefin Metathesis/Photoredox Catalysis.

Ruthenium(II) alkylidene complexes such as the Grubbs’ 1st and 2nd generation catalysts undergo a ligand substitution with 2,2′‐bipyridine, which readily leads to the common photoredox catalyst Ru(bpy)3 2+. The application of this catalyst transformation in sequential olefin metathesis/photoredox catalysis is demonstrated by way of ring‐closing metathesis (RCM)/photoredox ATRA reactions.

First total synthesis of 5(S)-hydroxyrecifeiolide

The first total synthesis of recently isolated 5(S)-hydroxyrecifeiolide has been described in ten straight forward linear steps with 14% of overall yield. The key reaction involves Jacobsen’s hydrolytic kinetic resolution, Copper catalysed Grignard reaction, Steglich esterification and ring closing metathesis reaction using Grubb's 2nd generation catalyst making the synthesis very elegant and simple. The stereogenic center at C5 was generated via Jacobsen's HKR which was confirmed by the Mandelate ester strategy as well as HPLC purity.

Investigating the effects of bulky allylic substituents on the regioregularity and thermodynamics of ROMP on cyclopentene

The interplay between equilibrium ROMP thermodynamics and the regioregular insertion of allylic trialkylsiloxy-substituted cyclopentenes during propagation with Hoveyda-Grubbs 2nd generation catalyst at varying temperatures is investigated. In general, bulkier substituents reduce monomer conversion and increase regioregular insertion. However, polymerization entropy (ΔSp) also appears to play an important role on ROMP thermodynamics when compared to ring strain (ΔHp) which is typically the parameter of focus for the efficacy of low-strain monomer conversion. This analysis has allowed for the determination of a “Goldilocks” monomer (i.e. one that provides the best compromise of monomer conversion (56% conversion at −10 °C) and regioregularity (97% HT insertion) to be 3-(tert-butyldimethylsiloxy)cyclopentene which has never before been explored or reported. Due to this study, this monomer has now been identified as the ideal choice for isotactic polypentenamer studies moving forward.

Strong Interaction with Carbon Filler of Polymers Obtained by Pyrene Functionalized Hoveyda-Grubbs 2nd Generation Catalyst.

Hoveyda-Grubbs 2nd generation catalyst that has the alkylidene functionalized with pyrene (HG2pyrene) was synthesized and characterized. This catalyst can be bound to carbonaceous filler (graphite, graphene or carbon nanotubes) by π-stacking interaction, but, since the catalytic site become poorly accessible to the incoming monomer, its activity in the ROMP (Ring Opening Metathesis Polymerization) is reduced. This is due to the fact that the above interaction also occurs with the aryl groups of NHC ligand of the ruthenium, as demonstrated by nuclear magnetic resonance and by fluorescence analysis of a solution of the catalyst with a molecule that simulated the structure of graphene. Very interesting results were obtained using HG2pyrene as a catalyst in the ROMP of 2-norbornene and 1,5-cyclooctadiene. The activity of this catalyst was the same as that obtained with the classical commercial HG2. Obviously, the polymers obtained with catalyst HG2pyrene have a pyrene as a chain end group. This group can give a strong π-stacking interaction with carbonaceous filler, producing a material that is able to promote the dispersion of other materials such as graphite in the polymer matrix.

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.

Synthesis of Cinchona Alkaloid Derived Chiral Squaramide Polymers by ADMET Polymerization and Their Application to Asymmetric Catalysis

The synthesis of cinchona alkaloid-derived chiral squaramide polymers using acyclic diene metathesis (ADMET) polymerization over Hoveyda-Grubbs 2nd generation catalysts (HG2) is reported herein. Th...