First-generation Catalyst Research Articles

Stereocontrolled Synthesis of Phosphoproline Analogues Containing a trans-Fused Octahydroindole Bicyclic System.

Herein we report for the first time the diastereoselective synthesis of (2R,3aR,7aS)- and (2S,3aS,7aR)-octahydroindole-2-phosphonic acid (OicP trans-fused stereoisomers) from diethyl (R)- and (S)-phosphopyroglutamate derivative. The key steps of this procedure are the ruthenium tetroxide oxidation of enantiomerically pure diethyl (R)- and (S)-phosphoprolinate obtained through Katritzky's benzotriazole-oxazolidine methodology, a highly diastereoselective successive double 4,5-diallylation of diethyl (R)- and (S)-phosphopyroglutamate with allyl bromide and allyltrimethylsilane with a trans-addition mode, and a ring-closing metathesis with Grubbs' first-generation ruthenium catalyst.

Influence of the Norbornene Anchor Group in Ru-Mediated Ring-Opening Metathesis Polymerization: Synthesis of Linear Polymers

Ring-opening metathesis polymerization (ROMP) mediated by Grubbs’ first-generation catalyst [G1, (PCy3)2(Cl)2RuCHPh] and Grubbs’ third-generation catalyst [G3, (H2IMes)(Cl)2(pyr)2RuCHPh] can exhibit living characteristics for some monomer classes, most commonly substituted norbornenes. Here, we studied how various anchor groups, the series of atoms connecting the polymerizable norbornene unit to a functional group, affect livingness in ROMP in a series of small-molecule exo-norbornene monomers. We first designed and calculated the HOMO energy of 61 monomers using density functional theory methods, finding that these energies spanned a range of 25 kcal/mol. We then performed kinetics experiments using 1H NMR spectroscopy to measure the propagation rate constant (kp,obs) under identical conditions for eight selected monomers with different anchor groups across the range of HOMO energies. We observed a positive correlation between the HOMO energy or the HOMO/LUMO energy gap and measured kp,obs values for both catalysts, revealing a 30-fold and a 10-fold variation in kp,obs values across the series for G1 and G3, respectively. Interestingly, we observed a plateau for the three monomers with the highest HOMO energies for G3 catalyst, suggesting that above a certain level, the HOMO energy no longer influenced the rate-determining step under the conditions studied here. Chelation studies revealed that only one of the eight monomers showed measurable binding of electron-rich groups on the monomer to the catalyst, but with no apparent effect on kp. Finally, we utilized 1H NMR spectroscopy to measure the rate of catalyst decomposition in the presence of each monomer, a key termination pathway in ROMP. Ultimately, we determined that the anchor group did not substantially affect catalyst decomposition, a proxy for the termination rate constant (kt). In sum, these combined computational and experimental studies collectively demonstrate that livingness in ROMP of exo-norbornene monomers using G1 and G3 catalysts, as measured by relative kp/kt ratios, is primarily controlled by the kp of the anchor group, which is correlated with the HOMO energy.

Design and Preparation of Ethylene Fluorescence Probes Based on Arylolefins and Grubbs Catalysts.

To detect the plant hormone ethylene, three arylolefins were employed to react with ethylene based on olefin metathesis. In this study, three fluorescence probes were successfully prepared using a first-generation Grubbs catalyst (G-1) and arylolefin with terminal vinyl groups. The probes were characterized using various techniques, including UV-vis, fluorescence, FT-IR, 1H NMR, 13C NMR, and 31P NMR spectroscopies and HRMS. The probes exhibited an emission maximum at 394 nm and showed excellent ethylene response. The detection limits for the probes were calculated to be 0.128, 0.074, and 0.188 μL/mL (3σ), respectively, based on fluorescence stimulation by ethylene gas. Additionally, the YGTZ-2 probe was used to detect ethylene gas during the storage process of tomatoes. This work expands the application of arylolefin in ethylene detection and provides a foundation for the development of economic, rapid, and convenient photosensitive sensors for ethylene in the future.

Synthesis and Cytotoxicity Evaluation of Betulin Cycloolefin Derivatives by Ruthenium-Catalyzed Ring-Closing Metathesis.

The combination of ring-closing metathesis with betulin enables the design and synthesis of novel biomolecules representing a library of triterpenoid derivatives for potential pharmacological research. In this work, cyclic olefin betulin derivatives were attempted to be prepared by the combination of ring-closing metathesis with betulin. Dicyclohexyl carbodiimide coupling reaction allowed the transformation of betulin into two types of linear olefin derivatives that have different methylene spacer lengths between the olefin and ester groups. Subsequently, betulin-based cycloolefins were synthesized by ring-closing metathesis using Grubbs first-generation catalyst. The influence of different parameters including solvents, temperature, catalysts, and catalyst loading on ring-closing metathesis was investigated. Cytotoxicity results indicated that these betulin-based olefin derivatives, derived from renewable bioresources, have potential applications in the biomedical field.

Rational Design of a Facially Coordinating P,N,N Ligand for Manganese-Catalysed Enantioselective Hydrogenation of Cyclic Ketones.

DFT calculations on the full catalytic cycle for manganese catalysed enantioselective hydrogenation of a selection of ketones have been carried out at the PBE0-D3PCM //RI-BP86PCM level. Mn complexes of an enantiomerically pure chiral P,N,N ligand have been found to be most reactive when adopting a facial coordination mode. The use of a new ligand with an ortho-substituted dimethylamino-pyridine motif has been calculated to completely transform the levels of enantioselectivity possible for the hydrogenation of cyclic ketones relative to the first-generation Mn catalysts. In silico evaluation of substrates has been used to identify those likely to be reduced with high enantiomer ratios (er), and others that would exhibit less selectivity; good agreements were then found in experiments. Various cyclic ketones and some acetophenone derivatives were hydrogenated with er's up to 99 : 1.

Synthesis of pyrrole derivatives via ring closing metathesis, Clauson‐Kaas reaction and Paal‐Knorr condensation as key steps

Herein, we report three simple methods for the synthesis of pyrrole derivatives starting with commercially available amines. Using Grubbs first-generation catalyst (G-I) one pot ring closing metathesis (RCM) and aromatization sequence was realized to assemble pyrrole deivatives without the use of any additional reagents. The second and third methods rely on, the condensation of 2,5-hexanedione/2,5-dimethoxy tetrahydrofuran in the presence of a low melting mixture of N, N'-dimethylurea (DMU) and L-(+)-tartaric acid (TA) and glacial acetic acid to produce substituted pyrroles in excellent yield. We also studied the photophysical properties of these molecules by fluorescence spectroscopic data which possess good quantum yield (ΦF).

A Single Functionalization Agent for Heterotelechelic ROMP Polymers.

Heterotelechelic polymers are an important class of materials finding applications in bioconjugation, imaging, sensing, and synthesis of organic/inorganic hybrid systems with interesting features. However, the synthesis of such polymers is challenging. Here, we report a mechanistically unique and most efficient method based on a single functionalization agent to prepare heterotelechelic polymers by a ring-opening metathesis polymerization. Different functionalization agents can be synthesized in one simple step from inexpensive commercial starting materials. The functionalization agents initially generate a functional initiator from commercial Grubbs' first-generation ruthenium benzylidene catalyst. During this process, a functional dihydrofuran derivative is produced. After functional initiation and propagation of a suitable monomer, the dihydrofuran derivative functionally terminates the polymerization yielding a primary alcohol-terminated heterotelechelic polymer. Molecular weight control is achieved by varying the ratio between monomer and Grubbs' first-generation catalyst. This method may emerge as a popular choice to prepare heterotelechelic polymers due to its simplicity and efficiency.

ESTUDO ONE-POT DA APLICAÇÃO DO CATALISADOR DE GRUBBS DE PRIMEIRA GERAÇÃO EM REAÇÕES DE METÁTESE DA PIPERINA E EUGENOL: A INFLUÊNCIA DA LIGAÇÃO DUPLA TERMINAL

ONE-POT STUDY OF THE APPLICATION OF CATALYST FIRST-GENERATION GRUBBS IN METATHESIS REACTIONS OF PIPERINE AND EUGENOL: THE INFLUENCE OF THE DOUBLE- BOND TERMINAL. In this paper, the piperine (PIP) and eugenol (EUG) organic compounds were used as substrates in olefin metathesis reactions catalyzed by first-generation Grubbs catalyst (G1) – [RuCl2(PCy3)2(=CHPh)], Cy is cyclohexyl and Ph is phenyl, in a one-pot system. The reactions occurred at 50 ºC, for 24, 48, or 96 h using the two substrates simultaneously in the ratio Ru:PIP:EUG of 1:1:1 and 1:10:10 mol. The results were evaluated by GC-MS, discussed in terms of the electronic and steric characteristics of the G1, and the structural proprieties of the substrates. In the Ru:PIP:EUG ratio of 1:1:1 mol, a dimeric species was observed for the olefin metathesis of EUG, in all time studied and in an additional experiment at 70 ºC for 48 h. When the Ru:PIP:EUG ratio was 1:10:10 mol, this dimer was not observed. Isomerization processes also were observed at all temperatures and catalyst:substrates ratio. The reaction yield increased with the raise of substrates amount. There was no cross-metathesis reaction. This fact was attributed to the chelating effect of the double coordination of the PIP to the catalyst.

Imprinted Glass Fiber-Reinforced Polymer Vascular Networks for Creating Self-Healing Wind Turbine Blades

Abstract Self-healing wind turbine blades can reduce costs associated with maintenance, repair, and energy compensation. Self-healing is the ability to sustain and recover from damage autonomously. We discuss the efforts made to optimize the self-healing properties of wind turbine blades and provide a new system to maximize this offset. This system utilizes vacuum-assisted resin transfer molding (VARTM), and 3D printed templates to imprint a vascular network onto a single glass fiber-reinforced polymer (FRP) sheet. This imprinted layer is infused with Grubbs first-generation catalyst and filled with dicyclopentadiene (DCPD) which is then sealed using plastic sheeting. The sealed imprint layer is embedded into a larger multilayer FRP prior to VARTM. After VARTM, the completed multilayer FRP is fully capable of self-healing microcracks. Three-dimensional printed templates with square grid and hexagonal patterns were used to evaluate how differences in DCPD distribution affect overall recovery. Three-point bending tests were performed to obtain the maximum flexural strengths of the FRP samples before and after self-healing to evaluate recovery. Overall, with the imprint layer method, the catalyst was focused in one area of the complete FRP, reducing the amount of unused catalyst present in the FRP. Also, the samples created using the imprint method were able to achieve a maximum average recovery of over 200% and a storage efficiency of 100%.

Routes to High-Performing Ruthenium-Iodide Catalysts for Olefin Metathesis: Ligand Lability Is Key to Efficient Halide Exchange.

Clean, high-yielding routes are described to ruthenium–diiodide catalysts that were recently shown to enable high productivity in olefin metathesis. For the second-generation Grubbs and Hoveyda catalysts (GII: RuCl2(H2IMes)(PCy3)(=CHPh); HII: RuCl2(H2IMes)(=CHAr), Ar = C6H4-2-OiPr), slow salt metathesis is shown to arise from the low lability of the ancillary PCy3 or ether ligands, which retards access to the four-coordinate intermediate required for efficient halide exchange. To exploit the lability of the first-generation catalysts, the diiodide complex RuI2(PCy3)(=CHAr) HI-I2 was prepared by treating “Grubbs I” (RuCl2(PCy3)2(=CHPh), GI) with NaI, H2C=CHAr (1a), and a phosphine-scavenging Merrifield iodide (MF-I) resin. Subsequent installation of H2IMes or cyclic (alkyl)(amino)carbene (CAAC) ligands afforded the second-generation iodide catalysts in good to excellent yields. Given the incompatibility of the nitro group with a free carbene, the iodo-Grela catalyst RuI2(H2IMes)(=CHAr′) (nG-I2: Ar′ = C6H3-2-OiPr-4-NO2) was instead accessed by sequential salt metathesis of GI with NaI, installation of H2IMes, and finally cross-metathesis with the nitrostyrenyl ether H2C=CHAr′ (1b), with MF-I as the phosphine scavenger. The bulky iodide ligands improve the selectivity for macrocyclization in ring-closing metathesis.

Multiblock Copolymers of Norbornene and Cyclododecene: Chain Structure and Properties.

We investigate the structure–property relations of the multiblock copolymers of norbornene with cyclododecene synthesized via the macromolecular cross-metathesis reaction between amorphous polynorbornene and semicrystalline polydodecenamer in the presence of the first-generation Grubbs catalyst. By adjusting the reaction time, catalyst amount, and composition of the initial system, we obtain a set of statistical multiblock copolymers that differ in the composition and average length of norbornene and dodecenylene unit sequences. Structural, thermal, and mechanical characterization of the copolymers with NMR, XRD, DSC (including thermal fractionation by successive self-nucleation and annealing), and rotational rheology allows us to relate the reaction conditions to the average length of crystallizable unit sequences, thicknesses of corresponding lamellas, and temperatures of their melting. We demonstrate that isolated dodecenylene units can be incorporated into crystalline lamellas so that even nearly random copolymers should retain crystallinity. Weak high-temperature endotherms observed in the multiblock copolymers of norbornene with cyclododecene and other cycloolefins could indicate that the corresponding systems are microphase-separated in the melt state.

Selective Ring-Opening Allene Metathesis: Polymerization or Ruthenium Vinylidene Formation.

Selective ring-opening allene metathesis polymerization (ROAlMP) and ruthenium vinylidene formation from 1,2-cyclononadiene (1) by simple catalyst selection are discussed. Grubbs second-generation catalyst (G2) favors the formation of an alkylidene leading to the ROAlMP of (1). Grubbs first-generation catalyst (G1) favors vinylidene formation and prevents the homopolymerization of (1) even at elevated temperatures. Isolation and characterization of poly(1) by NMR analysis and MALDI-TOF confirms the generation of a well-defined polyallene that exhibits good thermal stability (TD ca. 390 °C) and fluorescent properties. Ring-opening metathesis polymerization (ROMP) of a highly strained norbornene derivative (NBE-iPr) at 80 °C using the ruthenium vinylidene generated from (1) is also investigated. The discovery of ROAlMP allows for the simple access of well-defined polyallenes from commercially available catalysts and will ultimately guide structure-property determinations of polyallenes.

Sputtered highly effective iridium catalysts: a new approach for green satellite propulsion

This work demonstrated the large potential of sputtered iridium metal for catalytic reactions shown by the example of decomposition of hydrogen peroxide (H2O2) for space propulsion systems. For this purpose, iridium was coated onto Al2O3 pellets by a sputter process under varied process parameters. Depending on previously selected parameters, the obtained metal-loaded pellets offer closed- and/or open-shell structures. Catalytic productivity of these first-generation iridium-sputtered catalysts was estimated in laboratory experiments and compared to platinum-loaded pellets. Under optimized sputter-process conditions, the reactivity is significantly improved compared to the platinum-impregnated pellets. The better catalytic productivity can be explained by the increased active surface area of the iridium layers on the pellets. The surface morphology and the microstructure of the iridium coating can be actively controlled by the sputter pressure. The results are in accordance with the sputtering process pressure tendency described by the Thornton Structure–Zone Model.Graphical abstract

Formation of Supramolecular Polymer Network and Single-Chain Polymer Nanoparticles via Host–Guest Complexation from Pillar[5]arene Pendant Polymer

A pillar[5]arene pendant polymer was synthesized by ring-opening metathesis polymerization using the Grubbs first-generation catalyst and cross-linked using a bis(imidazolium) cross-linker via host...

Sixth-generation of ziegler-natta catalyst for homopolymer polypropylene polymerization: Effect to product properties and regulation

The development of catalysts for polypropylene (PP) polymerization has begun since Ziegler-Natta (Z-N) discovered the catalyst for polyethylene polymerization. However, the first-generation catalyst which was a combination of TiCl3-AlEt2Cl (catalyst-co-catalyst) has low productivity and isotacticity. The modifications continue to be made to increase the productivity and isotacticity by combining the Z-N catalyst with MgCl2, internal donors, and external donors. The fourth-generation Z-N catalyst, TiCl4/Phthalate/MgCl2-AlEt3/Silane, has given satisfactory results with high productivity and isotacticity. Another concern arose when phthalate derivatives turned out to be able to initiate cancer formation. This problem has led catalyst development to the sixth-generation Z-N catalyst with a phthalate-free internal donor. This research intends to study the effects of sixth-generation catalysts to polypropylene properties when compared to the fourth-generation catalysts. We produced homopolymer polypropylene (HPP) by fourth- and sixth-generation of Z-N catalyst with the same polymerization technology. Then, the effects on product properties, namely melt flow rate (MFR), xylene soluble, residual catalyst, physical properties, optical properties, and rheological properties were observed. Sixth-generation catalyst exhibited a better stereoregularity and it made a better flexural modulus. The rheological properties showed the sixth-generation catalyst products have lower molecular weight and it generates fewer gels and lower impact strength. Sixth-generation catalyst also exhibited lower catalyst residue which allows lower dosage of an acid scavenger with comparable color performance. With increasingly strict restrictions on the use of phthalates, the sixth-generation catalyst is more convenient to use. In terms of the effect on the polypropylene properties, fourth-and sixth-generation catalysts have their respective advantages.

Stereospecific Synthesis of Poly(methylene-E-vinylene) by Ring Opening Metathesis Polymerization of Substituted Cyclopropene Using Grubbs Catalysts

A first-generation Grubbs catalyst has been shown to not only catalyze the ring opening metathesis polymerization (ROMP) of cyclopropene derivatives but also differentiate E- and Z-double bonds in ...

Cross-Metathesis between Polynorbornene and Poly(5,6-epoxy-1-octenamer)

The macromolecular reaction of interchain cross-metathesis between polynorbornene and poly(5,6-epoxy-1-octenamer) in the presence of the first-generation Grubbs catalyst is studied. Chemically stable poly(5,6-epoxy-1-octenamer) is obtained through metathesis polymerization of 5,6-epoxycyclooct-1-ene with the second-generation Grubbs ruthenium catalyst. New random multiblock copolymers of norbornene and 5,6-epoxycyclooct-1-ene with different average block lengths determined by the reaction time, solvent type, and concentrations of the catalyst and initial homopolymers are synthesized and characterized by NMR, GPC, and DSC. Despite a distance between the epoxy substituent and the reaction center (double bond), poly(5,6-epoxy-1-octenamer) shows a lower activity in the cross-metathesis reaction with polynorbornene compared to unsubstituted polyoctenamer. The influence of epoxy groups present in the backbones of homopolymer and norbornene–cyclooctene multiblock copolymers on their thermal characteristics is studied. It is shown that the glass transition and melting temperatures increase with the concentration of epoxy groups upon the incorporation of an oxirane fragment into both homopolymers and copolymers. The crystallinity of poly(5,6-epoxy-1-octenamer) increases with the content of trans-С=С bonds in the polymer.

Synthesis and Gas-Separation Properties of New Silacyclopentane-Containing Polynorbornenes

Previously, it was shown that the presence of bulky silicon-containing substituents in the monomer unit of metathesis polynorbornenes hinders the postmodification and, in particular, exhaustive gem-difluorocyclopropanation of main-chain double bonds. In order to reduce the double bonds shielding by substituents, a new polynorbornene with a dimethylsilacyclopentane fragment in the monomer unit, poly(4,4-dimethyltricyclo[5.2.1.02,6]-4-siladec-8-ene) (PNBCP), is synthesized, in which the silylmethyl group is moved further from the double bonds. In order to achieve this, the monomer 4,4-dimethyltricyclo[5.2.1.02,6]-4-siladec-8-ene (NBCP) is first obtained via the diene condensation of 1,3-cyclopentadiene and 1,1-dichlorosilacyclopent-3-ene with following methylation of Si-Cl bonds. NBCP is polymerized by the ring-opening metathesis scheme in the presence of the first-generation Grubbs catalyst, Cl2(PCy3)2Ru=CHPh. The new polymer PNBCP is obtained in a yield of 99–100% and characterized. The gem-difluorocyclopropanation of PNBCP with difluorocarbene, generated during the thermolysis of sodium chlorofluoroacetate, is studied; the conditions for exhaustive replacement of double bonds by gem-difluorocyclopropane are found. It is shown that PNBCP is more active in postmodification compared to poly(5-trimethylsilyl)norbornene but is less active than unsubstituted polynorbornene. It is demonstrated that the introduction of the silacyclopentane fragment into the monomer unit of the metathesis polynorbornene and its subsequent difluorocyclopropanation lead to increase in gas permeability and diffusion and cause a slight decrease in ideal separation selectivities. It is found that gem-difluorocyclopropanation increases the glass transition temperature of PNBCP by 60°C and makes its films stable when stored in air.

Palladium- and Ruthenium-Catalyzed Intramolecular Carbene CAr -H Functionalization of γ-Amino-α-diazoesters for the Synthesis of Tetrahydroquinolines.

A synthetic method to prepare tetrahydroquinoline-4-carboxylic acid esters has been developed through the transition-metal-catalyzed intramolecular aromatic C-H functionalization of α-diazoesters. Both [{Pd(IMes)(NQ)}2 ] (IMes=1,3-dimesitylimidazol-2-ylidene, NQ=1,4-naphthoquinone) and the first-generation Grubbs catalyst proved effective for this purpose. The ruthenium catalyst was found to be the most versatile, although in a few cases the palladium complex afforded better yields or selectivities. According to DFT calculations, Pd0 - and RuII -catalyzed sp2 -CAr -H functionalization proceeds through different reaction mechanisms. Thus, the Pd0 -catalyzed reaction involves a Pd-mediated 1,6-H migration from the sp2 -CAr -H bond to the carbene carbon atom, followed by a reductive elimination process. In contrast, electrophilic addition of the ruthenacarbene intermediate to the aromatic ring and subsequent 1,2-proton migration are operative in the Grubbs catalyst promoted reaction.

Elucidation of the Reaction Mechanism of C2 + N1 Aziridination from Tetracarbene Iron Catalysts.

A combined computational and experimental study was undertaken to elucidate the mechanism of catalytic C2 + N1 aziridination supported by tetracarbene iron complexes. Three specific aspects of the catalytic cycle were addressed. First, how do organic azides react with different iron catalysts and why are alkyl azides ineffective for some catalysts? Computation of the catalytic pathway using density functional theory (DFT) revealed that an alkyl azide needs to overcome a higher activation barrier than an aryl azide to form an iron imide, and the activation barrier with the first-generation catalyst is higher than the activation barrier with the second-generation variant. Second, does the aziridination from the imide complex proceed through an open-chain radical intermediate that can change stereochemistry or, instead, via an azametallacyclobutane intermediate that retains stereochemistry? DFT calculations show that the formation of aziridine proceeds via the open-chain radical intermediate, which qualitatively explains the formation of both aziridine diastereomers as seen in experiments. Third, how can the formation of the side product, a metallotetrazene, be prevented, which would improve the yield of aziridine at lower alkene loading? DFT and experimental results demonstrate that sterically bulky organic azides prohibit formation of the metallotetrazene and, thus, allow lower alkene loading for effective catalysis. These multiple insights of different aspects of the catalytic cycle are critical for developing improved catalysts for C2 + N1 aziridination.