Hybrid Organic‐Inorganic Materials Derived from a Monosilylated Hoveyda‐type Ligand as Recyclable Diene and Enyne Metathesis Catalysts

The synthesis of a monosilylated Hoveyda‐type monomer is described as well as the preparation of several organic‐inorganic hybrid materials derived from it by sol‐gel processes and by anchoring to commercial silica gel and MCM‐41. The resulting materials were treated with first and/or second generation Grubbs’ catalyst to generate Hoveyda–Grubbs’ type alkylidene ruthenium complexes covalently bonded to the silica matrix. These materials are efficient recyclable catalysts for the ring‐closing metathesis reaction of dienes and enynes, even for the formation of tri‐ and tetrasubstituted olefins.     

New Indenylidene‐Schiff Base‐Ruthenium Complexes for Cross‐Metathesis and Ring‐Closing Metathesis

We here report on the stability and catalytic activity of new indenylidene‐Schiff base‐ruthenium complexes 3a – f through representative cross‐metathesis (CM) and ring‐closing metathesis (RCM) reactions. Excellent activity of the new complexes was found for the two selected RCM reactions; prominent conversion was obtained compared to the commercial Hoveyda–Grubbs catalyst 2 . Moreover, excellent results were obtained for a standard CM reaction. Higher conversions were achieved with one of the indenylidene catalysts compared with Hoveyda–Grubbs catalyst. Unexpectedly, an isomerization reaction was observed during the CM reaction of allylbenzene. To the best of our knowledge, isomerization reactions in this model CM reaction in closed systems have never been described using first generation catalysts, including the Hoveyda–Grubbs catalyst. The first model CM reactions as well as the RCM reactions have been monitored using ¹H NMR. The course of the CM reaction of 3‐phenylprop‐1‐ene ( 8 ) and cis‐1,4‐diacetoxybut‐2‐ene ( 9 ) was monitored by GC. The isomerization reaction was studied by means of GC‐mass spectrometry and in situ IR spectroscopy. All catalysts were structurally characterized by means of ¹H, ¹³C, and ³¹P NMR spectroscopy.     

Silica Immobilized Second Generation Hoveyda‐Grubbs: A Convenient,Recyclable and Storageable Heterogeneous Solid Catalyst

The second generation Hoveyda–Grubbs metathesis catalyst was successfully immobilized on silica in pellet and powder form following a practical and fast synthesis procedure. The activity of the solid system is truly heterogeneous, efficient in various metathesis reaction types and stable for at least 4000 TON. Ru contamination of the products was very low (ppb levels). The successful use of the robust system has been demonstrated in a continuous reactor set‐up.     

Mesocellular Foam‐Supported Catalysts: Enhanced Activity and Recyclability for Ring‐Closing Metathesis

Although ring‐closing metathesis (RCM) has been one of the most powerful methodologies for creating cyclic compounds, the pharmaceutical industry has not yet widely adopted this process commercially due to the high costs and leaching problems of homogeneous ruthenium catalysts. To circumvent these problems, we have immobilized the second‐generation Hoveyda–Grubbs catalyst effectively onto siliceous mesocellular foam (MCF). The open and interconnected pores of MCF facilitated ligand immobilization and substrate diffusion. We have observed that the ligand and metal loadings significantly affected the catalytic activity and recyclability. Enhanced recyclability by suppression of ruthenium leaching was achieved by using excess immobilized ligands. The resulting novel heterogenized catalysts demonstrated excellent activity and reusability for the RCM of various types of substrates.     

Unexpected Results of a Turnover Number (TON) Study Utilising Ruthenium‐Based Olefin Metathesis Catalysts

A turnover number (TON) study of ruthenium‐based metathesis catalysts has been conducted for ring‐closing metathesis (RCM) in dilute solution. Unexpectedly the results indicate that 1^st generation metathesis catalysts can give higher TON in RCM of simple unsubstituted terminal olefins than their second generation counterparts. In particular, the 1^st generation Hoveyda–Grubbs catalyst showed unexpectedly high activity, particularly when compared to the 2^nd generation catalysts.     

Self‐healing materials for structural applications

Self‐healing materials for structural applications offer considerable practical benefits because they would allow to overcome the difficulties connected to damage diagnosis and repair. In this article, a process active at very low temperature for the repair of damaged structural material is shown. The self‐repair function is based on the metathesis polymerization of ENB activated by Hoveyda–Grubbs' first generation catalyst. The self‐healing epoxy mixture, containing the catalyst powder allows a cure temperature up to 180°C. Dynamic mechanical analysis was used to determine mechanical parameters. The autorepair composite shows a high modulus in a wide temperature range, a glass transition temperature at about 100°C and a self‐healing efficiency of about 95%. POLYM. ENG. SCI., 54:777–784, 2014. © 2013 Society of Plastics Engineers     

Site‐Directed and Global Incorporation of Orthogonal and Isostructural Noncanonical Amino Acids into the Ribosomal Lasso Peptide Capistruin

Expansion of the structural diversity of peptide antibiotics was performed through two different methods. Supplementation‐based incorporation (SPI) and stop‐codon suppression (SCS) approaches were used for co‐translational incorporation of isostructural and orthogonal noncanonical amino acids (ncAAs) into the lasso peptide capistruin. Two ncAAs were employed for the SPI method and five for the SCS method; each of them probing the incorporation of ncAAs in strategic positions of the molecule. Evaluation of the assembly by HR‐ESI‐MS proved more successful for the SCS method. Bio‐orthogonal chemistry was used for post‐biosynthetic modification of capistruin congener Cap_Alk10 containing the ncAA Alk (Nε‐Alloc‐L ‐lysine) instead of Ala. A second‐generation Hoveyda–Grubbs catalyst was used for an in vitro metathesis reaction with Cap_Alk10 and an allyl alcohol, which offers options for post‐biosynthetic modifications. The use of synthetic biology allows for the in vivo production of new peptide‐based antibiotics from an expanded amino acid repertoire.     

Highly Active Silica Gel‐Supported Metathesis (Pre)Catalysts

Highly active Hoveyda–Grubbs and Hoveyda–Blechert type (pre)catalysts, immobilized on silica gel, are presented. These (pre)catalysts are synthesized in a few steps from readily available precursors and demonstrate high activity in a number of test metathesis reactions. The catalyst is easily separated by simple filtration of the non‐swelling material.     

Synthesis and characterization of accordion main‐chain azo‐dye polymers for second‐order optical non‐linearity

New type accordion polymers with azo‐dye chromophores as the major segments (up to 70% by weight) of the main chain for second optical non‐linearity (NLO) are designed and synthesized by the Knoevenagel polycondensation between bis(carboxaldehyde) containing azobenzene and bis(cyanoacetate) comonomers. Several important properties for NLO application, such as solubility and thermal stability, are investigated, and the effects of linkage groups on the physical properties of polymers are also discussed in some detail. Poled films of one of these polymers show a relatively high resonant d₃₃ value of 33 pm V⁻¹ by second harmonic generation (SHG) measurement, and their order parameter, which is determined to be 0.20 by UV–vis measurement, keep almost constant for 240 h at ambient temperature. © 2000 Society of Chemical Industry     

A viable technology to generate third‐generation biofuel

First generation biofuels are widely available because the production technologies are well developed. However, growth of the raw materials conflicts with food security, so that first‐ generation biofuels are not so promising. The second generation of biofuels will not compete directly with food but requires several energy intensive processes to produce them, and also increases land‐use change, which reduces its environmental and economic feasibility. The production of third‐generation biofuels avoids the issues met with first‐ and second‐ generation biofuels, namely food–fuel competition, land‐use change, etc., and is thus considered a viable alternative energy resource. On all dimensions of sustainability (environmental, social and economical), a life cycle assessment approach is most relevant to avoid issues in problem shifting. The utilization of organic waste and carbon dioxide in flue gases for the production of biomass further increases the sustainability of third generation biofuels, as it minimizes greenhouse gas emissions and disposal problems. Copyright © 2011 Society of Chemical Industry     

Electric‐field‐induced layer‐by‐layer fabrication of stable second‐order nonlinear optical films

BACKGROUND: Second‐order nonlinear optical (NLO) films have been made using electric field poling polymer and Langmuir–Blodgett techniques with non‐centrosymmetric structures that exhibit relatively high values of nonlinear susceptibility (χ²), but the shortcomings of insufficient temporal or mechanical stability have restricted their potential applications. In this study, electric‐field‐induced layer‐by‐layer assembly was investigated as an effective technique to prepare low molecular weight chromophoric (LMWC) molecules of high degree of self‐ordering and density in NLO films. RESULTS: A new and stable LMWC molecule, 2‐({4‐[4‐(2‐carboxy‐2‐cyanovinyl)‐Z‐phenylazo]‐phenyl}‐methylamino)‐ethyl acid (DRCB), was first designed and synthesized successfully. The chromophore possesses two negative groups, one at each end, and still retains molecular polarity after ionization. DRCB was successfully assembled with polycationic diazoresin using the electric‐field‐induced layer‐by‐layer assembly method to construct stable organic second‐order NLO multilayer films. Upon UV irradiation, the interaction between multilayers was converted from an electrostatic interaction to covalent bonds. CONCLUSION: Due to the DC electric field effect in the assembly process, in addition to introducing the stable chromophore molecule and the covalent crosslinking structure in the films, the second‐order NLO films fabricated using the method described have large second harmonic generation response, good thermal stability and excellent chemical stability, which offer potential advantages for device applications. Copyright © 2009 Society of Chemical Industry     

Specific interactions in poly(styrene‐co‐2‐hydroxyethyl acrylate)/poly(styrene‐co‐N,N‐dimethylacrylamide) systems

Amphiphilic copolymers of poly(styrene‐co‐2‐hydroxyethyl acrylate) (SHEA) and poly(styrene‐co‐N, N‐dimethylacrylamide) (SAD) of different compositions were prepared by free radical copolymerization and characterized by different techniques. Depending on the nature of the solvent and the densities of interacting species incorporated within the polystyrene matrices, novel materials as blends or interpolymer complexes with properties different from those of their constituents were elaborated when these copolymers are mixed together. The specific interpolymer interactions of hydrogen bonding type and the phase behavior of the elaborated materials were investigated by differential scanning calorimetry (DSC) and Fourier transform infra red spectroscopy (FTIR). The specific interactions of hydrogen bonding type that occurred within the SHEA and within their blends with the SAD were evidenced by FTIR qualitatively by the appearance of a new band at 1626 cm^?1 and quantitatively using appropriate spectral curve fitting in the carbonyl and amide regions. The variation of the glass transition temperature with the blend composition behaved differently with the densities of interacting species. The thermal degradation behavior of the materials was studied by thermogravimetry. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

3D‐Printing of High‐κ Thiol‐Ene Resins with Spiro‐Orthoesters as Anti‐Shrinkage Additive

Tri(ethylene glycol) divinyl ether and the spiro‐orthoester 2‐((allyloxy)methy)‐1,4,6‐trioxospiro[4.4]nonane can be formulated in different ratios and crosslinked by thiol‐ene reactions. The spiro‐orthoester is used as anti‐shrinkage additive, enabling shrinkage reduction of up to 39%. Addition of a radical photoinitiator for the thiol‐ene reaction and a cationic photoinitiator for the double ring‐opening of the spiro‐orthoester enables dual‐curing for application in 3D‐printing. The formulation free of the spiro‐orthoester shows gelation during the printing process and, correspondingly, low resolution. The formulations containing the spiro‐orthoester exhibit higher resolutions in the range of 50 µm. The resins containing mixtures of tri(ethylene glycol) divinyl ether and the spiro‐orthoester show permittivities as high as 10⁴. The dielectric loss factor of the resins is in the range of 0.5–7.6, and the conductivity in the range of 1.3?10^?11 to 2.0?10^?11 S cm^?1. These high‐κ materials can be 3D‐printed by digital light processing for the next generation of electronic materials.     

A study on the preparation of polymer/montmorillonite nano‐composite materials by photo‐polymerization

The preparation of polymer/montmorillonite intercalation composite materials was studied by two kinds of photo‐polymerization reaction (photo‐acid generation and photo‐radical generation). Small‐angle X‐ray diffraction was used for the structural characterization of montmorillonite contained in the products. Results indicated that, after chemical modification of montmorillonite, the monomer (methyl methacrylate) and the prepolymer (m‐cresol/HMMM) were able to intercalate into the layers of clay and to polymerize ‘in situ’, thus producing photo‐polymerized composite materials. The advantages and shortcomings of the method of photo‐polymerization for the preparation of these composite materials are discussed. © 2001 Society of Chemical Industry     

Microwave‐Assisted Reversible Coordination‐Mediated Polymerization for Self‐Healing Hybrid Materials: RGO@PDA Simultaneous as Catalyst and Nanocomposites in One‐Pot

In this article, polydopamine (PDA) is efficiently adhered on the surface of graphene oxide (GO) by mussel‐inspired chemistry. The obtained reduced GO/PDA (RGO@PDA) nanocomposites are used for catalyzing reversible coordination‐mediated polymerization under microwave radiation. Well‐defined and iodine‐terminated polyacrylonitrile‐co‐poly(n‐butyl acrylate) (PAN‐co‐PnBA) is successfully fabricated by using RGO@PDA nanocomposites as catalysts. Importantly, green and novel strategy of PAN‐co‐PnBA‐type self‐healing nanocomposite materials is further fabricated with RGO@PDA as additive after polymerization as catalyst in one‐pot. As a reinforcement agent, RGO@PDA can also improve the mechanical and self‐healing properties of hybrid materials, which opens up a novel and green methodology for the preparation of self‐healing hybrid materials.     

Hydrogen‐bonded supramolecular polyurethanes

As a class of materials, supramolecular polymers represent an exciting area of advanced materials research. The combination of unique properties, easy synthesis and response to the environment or external and temporal stimuli makes them important as a focus for the next generation of materials. Understanding and manipulating the non‐covalent interactions leading to polymer assembly allows control over properties by selecting specific building blocks with well‐understood non‐covalent chemistry from an established toolkit. This allows assembly of defined and easily manipulated architectures, where physical characteristics similar to conventional high‐molecular‐weight polymers can be realized. Herein, we describe recent studies of the self‐assembly of polyurethane‐based supramolecular materials. © 2014 Society of Chemical Industry     

One‐Pot Olefin Isomerization/Aliphatic Enamine Ring‐Closing Metathesis/Oxidation/1,3‐Dipolar Cycloaddition for the Synthesis of Isoindolo[1,2‐a]isoquinolines

N‐Alkyl‐N‐(2‐vinylbenzyl)prop‐2‐en‐1‐amine derivatives undergo a one‐pot olefin isomerization/aliphatic enamine ring‐closing metathesis (RCM)/oxidation/1,3‐dipolar cycloaddition sequence with the ruthenium complex, Ru(CO)HCl(PPh₃)₃, a second generation Hoveyda–Grubbs catalyst, and a 1,3‐dipolarophile. Overall, in a single operation the reaction sequence converts simple benzylamine derivatives into isoindolo[1,2‐a]isoquinolines with a π‐conjugated four‐ring system, through three unique ruthenium‐catalyzed transformations.

     

Study of Antioxidative Properties of Some Mono Amino‐Acid‐Type and Dipeptide‐Type Surfactants

Surfactants of tryptophan, tyrosine, and histidine were successfully synthesized. They were then modified to obtain dipeptide‐type surfactants with better solubility in both polar and nonpolar solvents, giving more emphasis to the development of water‐soluble amino‐acid‐type surfactants. All developed materials were designed to have functionality as antioxidants (AOX). The investigation of free radical scavenging capacity at pre‐micellar concentrations revealed greater Trolox equivalent (TE, relative scavenging capacity to Trolox) results for Trp‐type surfactants followed by Tyr‐type and His‐type. As expected, the synthesized surfactants exhibited comparable AOX properties to their parent amino acids. The AOX behavior of these surfactants was also checked in micellar concentrations, and the trend was found to be analogous: Trp‐type > Tyr‐type > His‐type surfactants. However, all of them were acting as better AOX in the micellar state than in the monomeric state. Investigating the synergistic effect found no interaction between the “amino acid–surfactant” pairs or the “surfactant–surfactant” pairs with varying ratios. They showed total AOX activity with respect to that of each material. This work opens up the door to the application of some new oil and water‐soluble amino‐acid‐type surfactants having auspicious AOX activity.     

Metathesis of 1‐Octene in Ionic Liquids and Other Solvents: Effects of Substrate Solubility,Solvent Polarity and Impurities

With the self‐metathesis of 1‐octene to 7‐tetradecene catalyzed by Grubbs 1^st generation [benzylidene‐bis(tricyclohexylphosphine)dichlororuthenium, ( 1 )] precursor at low concentrations (0.02 mol %) as basis, the effects of the solubility of the substrate in ionic liquids, the solvent polarity, as well as the influence of various impurities stemming from the preparation of ionic liquids have been investigated. The solubility of the substrate in the ionic liquid has little effect on the conversion, and the reaction is not mass‐transfer limited. While a higher polarity of an organic solvent increases the rate, it is independent of the polarity excerted by the cation of an ionic liquid. Of paramount importance for reproducible results is the purity of ionic liquids. An extensive study shows that catalyst deactivation by impurities increases in the order of water<halide<1‐methylimidazole. In the presence of water or 1‐methylimidazole impurities, the Grubbs‐Hoveyda precursor ( 3 ) is superior to both the 1^st ( 1 ) and 2^nd ( 2 ) generation Grubbs complexes. Under impurity‐free conditions or in the presence of chloride, the performance of 2 is equivalent to that of 3 .     

Organically modified inorganic sol‐gel materials for second‐order nonlinear optics

A series of the organically modified inorganic NLO sol‐gel materials based on the prepolymer of alkoxysilanes and an alkoxysilane dye (ASD) have been investigated. Optically clear samples exhibit large second‐order optical nonlinearity (d₃₃ = ∼10.8–54.0 pm/V at 1064 nm) after poling and curing at 220°C for 1 h. The thermal behavior of these NLO sol‐gel materials was studied by temperature‐dependent dielectric relaxation. The results indicate that the crosslinking density of cured NLO sol‐gel materials was increased with increasing alkoxysilane content. Subsequently, better temporal stabilities were obtained for the poled/cured NLO sol‐gel materials with a higher alkoxysilane content. Moreover, the structural influence of alkoxysilanes on the thermal behavior and second‐order nonlinearity was also studied for these NLO sol‐gel materials. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1852–1859, 2001