Terminal Vinyl Research Articles

Template synthesis and X-ray structure of the tris-glyoximate iron(II) clathrochelates with terminal reactive groups

One-pot template condensation of glyoxime with the corresponding functionalized phenylboronic acids on an iron(II) ion as a matrix afforded 3- and 4-substituted phenylboron-capped tris-glyoximate iron(II) clathrochelates with terminal amine, formyl (acetal) and vinyl groups; those with acetal groups were converted into the formyl-terminated cage complexes using H+-catalyzed hydrolysis. The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV–Vis, 1H and 13C NMR spectroscopies, and by single crystal X-ray diffraction (for three of these clathrochelates). Their molecules possess a geometry intermediate between a trigonal prism (TP) and a trigonal antiprism (TAP) and the bite angles α remain almost constant being in the range 77–79°, whereas the heights h of FeN6-coordination polyhedra depend on the distortion angle φ values (from 12.2 to 20.7°) thus being in the range 2.36–2.37Å. An encapsulated iron(II) ion is situated almost in the centre of cage frameworks and the average chelate CC bonds in these tris-glyoximate frameworks are substantially shorter than those for their aliphatic and aromatic analogs. The crystal packings are governed by weak supramolecular hydrophobic interactions and an absence of the steric hindrances between the ribbed substituents (hydrogen atoms) allowed to form intermolecular π…π interactions.As follows from single crystal X-ray diffraction data, the synthesized macrobicyclic tris-glyoximates with reactive terminal groups, which the macrobicyclic molecules contain no bulky ribbed substituents, have large ligand aspect ratio and, therefore, they seem to be promising syntones and building blocks for preparation of covalent (including imine and amine) and coordination metallomacrocycles, MOFs and cages (capsules) with big voids and cavities as hosts, suitable for inclusion of various organic and inorganic guests.

Preparation and application of magnetic molecularly imprinted nanoparticles for the selective extraction of osthole in Libanotis Buchtomensis herbal extract.

In this work, novel magnetic molecularly imprinted polymers were prepared for the selective extraction of osthole from Libanotis Buchtomensis herbal extract. During the synthesis process, double bonds grafted on the surface of Fe3 O4 nanoparticles could not only drive the temple molecules to locate onto the surface of vinyl-functionalized magnetic nanoparticles by π-π conjugation, which makes the distribution of binding sites ordered, but also direct the occurrence of imprinting polymerization at the surface of magnetic nanoparticles by the copolymerization of vinyl terminal groups with functional monomers and cross-linking agent. The characteristics of the resulting polymers were evaluated by transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and vibrating sample magnetometry. Adsorption kinetics, isotherms, selectivity, reproducibility, and reusability were discussed, which suggest that the obtained nanomaterials possess rapid binding kinetics, high adsorption capacity of 17.65 mg/g, and favorable selectivity for the target molecule. Satisfactory reproducibility and reusability were verified as well. Meanwhile, the resultant imprinted nanoparticles were successfully applied to selectively separate osthole from the herbal extract, which show great potential in extracting active ingredients from traditional Chinese medicine.

Addition-curable type liquid silicone rubbers based on phenyl-containing organopolysiloxanes with terminal vinyl groups

A series of organosilicon rubbers of the addition-curable type containing dimethyland methylphenylsiloxy, or diphenylsiloxy units with terminal vinyl groups were synthesized and used for manufacturing liquid silicone rubbers (LSRs) by addition-curable vulcanization. The physical mechanical characteristics of the LSRs were studied. The obtained LSRs can find use at lower temperatures, since they have low glass transition temperatures, and dimethylsiloxane component crystallization is suppressed in them.

An efficient and straightforward route to terminal vinyl sulfones via palladium-catalyzed Suzuki reactions of α-bromo ethenylsulfones

A general and simple protocol for the synthesis of α-substituted alkenylsulfones has been developed firstly via palladium-catalyzed Suzuki reactions between α-bromo ethenylsulfones and organoborons. Using a catalyst composed of Pd(OAc)2 and SPhos, a variety of aryl, heteroaryl, and alkylboron reagents could efficiently couple with α-bromo ethenylsulfones under mild conditions. Moreover, it has been demonstrated for the first time that vinyl sulfones underwent smooth reduction by diimide generated from 2-nitrobenzenesulfonylhydrazide.

Highly Cis-1,4-Selective Living Polymerization of 3-Methylenehepta-1,6-diene and Its Subsequent Thiol–Ene Reaction: An Efficient Approach to Functionalized Diene-Based Elastomer

Living polymerization of 3-methylenehepta-1,6-diene (MHD) catalyzed by bis(phosphino)carbazoleide-ligated yttrium alkyl complex afforded a new product bearing pendant terminal vinyl groups with high stereotacticity (cis-1,4-selectivity up to 98.5%), proved by the NMR (1H, 13C, and 1D ROESY) spectroscopic analyses, which demonstrates overwhelmingly favorable chemoselectivity toward conjugated diene over α-olefin moieties. High cis-1,4 random copolymers of MHD and isoprene could also be obtained with pendant vinyl groups ranging from 10% to 90%. These vinyl groups in every chain unit can be cleanly and quantitatively converted into various functionalities via light-mediated thiol–ene reaction, resulting in homo- and copolymers of various functional butadiene derivatives, which display versatile thermal properties.

New synthesis of artepillin C, a prenylated phenol, utilizing lipase-catalyzed regioselective deacetylation as the key step.

We have synthesized artepillin C, a diprenylated p-hydroxycinnamate originally isolated from Brazilian propolis and exhibiting antioxidant and antitumor activities, from 2,6-diallylphenol. Replacement of the terminal vinyl with 2,2-dimethylvinyl group by olefin cross-metathesis and subsequent transformation yielded 2,6-diprenyl-1,4-hydroquinone diacetate. Candida antarctica lipase B-catalyzed deacetylation in 2-propanol regioselectively removed the less hindered acetyl group to give 2,6-diprenyl-1,4-hydroquinone 1-monoacetate. After triflation of the liberated 4-hydroxy group, a three-carbon side chain was introduced by palladium-mediated alkenylation with methyl acrylate. Final hydrolysis of the esters furnished artepillin C.

ON THE PROTECTIVE NATURE OF WAX COATINGS FOR CULTURALLY SIGNIFICANT OUTDOOR METALWORKS: MICROSTRUCTURAL FLAWS, OXIDATIVE CHANGES, AND BARRIER PROPERTIES

Changes in chemical, microstructural, and barrier properties of two commonly used and commercially available waxes – a microcrystalline wax (Renaissance wax) and a microcrystalline and carnauba blended wax (Butcher's Boston Polish Amber Paste Wax) – for the prevention of corrosion on outdoor metalwork were investigated. The waxes were applied to both plain and patinated substrates of bronze and steel, and properties of the films were measured before and after weathering. Accelerated weathering was performed by accelerated UV-B illumination/condensation and outdoor weathering under standard South Florida exposures and in Portland, OR.Comparison of Fourier transformed micro-infrared and nuclear magnetic resonance spectra enabled characterization of chemical functional groups of these waxes as they weathered and showed relative increases in methylene character suggestive of cross-linking, appearance of terminal vinyl bands suggestive of chain-scission, and evidence of oxidative film damage. After annealing, microstructural changes were observed by thin-film X-ray diffraction and showed a decrease in crystallinity, which indicates a decrease in barrier properties. The barrier properties of the wax films after weathering were studied by electrochemical impedance spectroscopy and equivalent electrical circuits provided insights into the physical state of the films. The electrochemical impedance spectroscopy data showed that the permittivity of the weathered waxed panels increased, which was observed as a decrease in coating resistance and an increase in coating capacitance. Photographic documentation of the substrates showed extensive visible corrosion upon weathering. Our results demonstrate that waxed metal panels exposed outdoors do not have a period of stability when the protective qualities of the film do not change. This suggests that while waxes are commonly used to protect against corrosion, their barrier properties are affected by flaws in the microstructure and their susceptibility to chemical alteration during weathering. Results from a blind study with professional conservators as the participants are presented, to elucidate how they rank the importance of such factors as gloss and working lifetime when selecting protective coatings.

The role of unsaturations in the Gamma irradiation of crosslinkable polymers

Abstract Nowadays, the understanding of the interaction of ionizing radiations with polymeric materials is becoming increasingly important. It is well known that many parameters regarding the synthesis of the polymers noticeably affect the irradiation process. In this work, an analysis of the effect of the type and the position of unsaturations in the molecular structure of crosslinkable polymers is performed. For such purpose, two solid semycristalline metallocenic ethylene 1-olefin copolymers (mEOC) which contain a low concentration of unsaturations from the synthesis, and their hydrogenated samples, were irradiated along with liquid poly(dimethylsiloxane) (PDMS) homo and copolymers containing different location and concentration of vinyl groups, which were structurally tailored through anionic synthesis. The source of irradiation was 60Co, under vacuum at room temperature, in all the cases. The results indicated that terminal vinyls drastically accelerate the crosslinking to lower doses, even at much lower concentrations than other type and location of unsaturations for both, mEOC and PDMS, type of polymers.

ChemInform Abstract: Pd‐Catalyzed Three‐Component Coupling of Terminal Alkynes, Arynes, and Vinyl Cyclopropane Dicarboxylate.

AbstractThe efficient protocol provides access to 1‐allyl‐2‐alkynylbenzenes.

Comparative DFT study of structure, reactivity and IR spectra of phosphorus-containing dendrons with P[dbnd]N[sbnd]P[dbnd]S linkages, vinyl and azide functional groups

Fourier transform IR spectra of the first generation dendrons built from thiophosphoryl core with terminal PCl groups, vinyl (G1) and azide (G2) functional group at the level of the core have been recorded. The optimized geometries of low energy isomers of G1 and G2 have been calculated by density functional (DFT) method at the PBE/TZ2P level of theory. DFT is used for analyzing the properties of each structural part (core, branches, surface). It was found that the repeated branching units of G1 and G2 contain planar OC6H4CHNN(CH3)P fragments. DFT results for the structure of G1 and G2 are in good agreement with X-ray diffraction measurements. A complete vibrational assignment is proposed for different parts of G1 and G2. The global and local reactivity descriptors have been used to characterize the reactivity pattern of the core functional and terminal groups. Natural bond orbital (NBO) analysis has been applied to comparative study of charge delocalization. Our study reveals why azide group linked to phosphorus has a different reactivity when compared to organic azides.

Synthesis of Two Subunits of the Macrolide Domain of the Immunosuppressive Agent Sanglifehrin A and Assembly of a Macrolactone Precursor. Application of Masamune anti-Aldol Condensation

Asymmetric anti-aldol coupling of a norephedrine-derived ester with an α-chiral aldehyde was used to synthesize a carboxylic acid representing the C13-C19 segment of the macrocyclic domain present in the immunosuppressive agent sanglifehrin A. Felkin addition set configuration at the C14-C17 stereotetrad in this unit in which hydroxyl functions at C15 and C17 were masked as an internal ketal. The carboxyl group of this segment was coupled to the N-terminus of the tripeptide portion (C1-N12) of sanglifehrin A macrolactone to assemble the C1-C19 domain. Synthesis of the C20-C25 subunit of sanglifehrin A containing a (23S) alcohol was completed via asymmetric allylation of (E)-3-iodo-2-methylprop-2-enal followed by oxidative cleavage of the terminal vinyl appendage and a Takai olefination with pinacol dichloromethylboronate. Esterification of this alcohol with a C1-C19 carboxylic acid furnished an open C1-C25 macrolactone precursor, but this substance failed to undergo macrocyclization via intramolecular Suzuki-Miyaura coupling.

Pd-Catalyzed Three-Component Coupling of Terminal Alkynes, Arynes, and Vinyl Cyclopropane Dicarboxylate

A palladium-catalyzed three-component coupling involving in situ generated arynes, terminal alkynes, and vinyl cyclopropane dicarboxylate has been developed. The process demonstrates the first example of aryne chemistry combined with the ring opening of vinyl cyclopropanes. This efficient method using readily available starting materials generates two new carbon-carbon bonds in one pot.

A combined crossed molecular beam and theoretical investigation of the reaction of the meta-tolyl radical with vinylacetylene--toward the formation of methylnaphthalenes.

Crossed molecular beam experiments and electronic structure calculations on the reaction of the meta-tolyl radical with vinylacetylene were conducted to probe the formation of methyl-substituted naphthalene isomers. We present the compelling evidence that under single collision conditions 1- and 2-methylnaphthalene can be formed without an entrance barrier via indirect scattering dynamics through a bimolecular collision of two non-PAH reactants: the meta-tolyl radical and vinylacetylene. The electronic structure calculations, conducted at the UCCSD(T)-F12b/cc-pVDZ//UM06-2x/cc-pVTZ + ZPE(UM06-2x/cc-pVTZ) level of theory, reveal that this reaction is initiated by the barrierless addition of the meta-tolyl radical to the terminal vinyl carbon (C1) of vinylacetylene, via a van-der-Waals complex implying that this mechanism can play a key role in forming methyl-substituted PAHs in low temperature extreme environments such as the low temperature interstellar medium and hydrocarbon-rich atmospheres of planets and their moons in the outer solar system. The reaction mechanism, proposed from the C11H11 potential energy surface, involves a sequence of isomerizations involving hydrogen transfer and ring closure, followed by hydrogen dissociation, which eventually leads to 1- and 2-methylnaphthalene in an overall exoergic process.

Computational evaluation of unsaturated carbonitriles as neutral receptor model for beryllium(II) recognition.

Design of neutral receptor molecules (ionophores) for beryllium(II) using unsaturated carbonitrile models has been carried out via density functional theory, G3, and G4 calculations. The first part of this work focuses on gas phase binding energies between beryllium(II) and 2-cyano butadiene (2-CN BD), 3-cyano propene (3-CN P), and simpler models with two separate fragments; acrylonitrile and ethylene. Interactions between beryllium(II) and cyano nitrogen and terminal olefin in the models have been examined in terms of geometrical changes, distribution of charge over the entire π-system, and rehybridization of vinyl carbon orbitals. NMR shieldings and vibrational frequencies probed charge centers and strength of interactions. The six-membered cyclic complexes have planar structures with the rehybridized carbon slightly out of plane (16° in 2-CN BD). G3 results show that in 2-CN BD complex participation of vinyl carbon further stabilizes the cyclic adduct by 16.3kcal mol(-1), whereas, in simpler models, interaction between beryllium(II) and acetonitrile is favorable by 46.4kcal mol(-1) compared with that of ethylene. The terminal vinyl carbon in 2-CN BD rehybridizes to sp (3) with an increase of 7% of s character to allow interaction with beryllium(II). G4 calculations show that the Be(II) and 2-CN BD complex is more strongly bound than those with Mg(II) and Ca(II) by 98.5 and 139.2kcal mol(-1) (-1), respectively. QST2 method shows that the cyclic and acyclic forms of Be(II)-2-CN BD complexes are separated by 12.3kcal mol(-1) barrier height. Overlap population analysis reveals that Ca(II) can be discriminated based on its tendency to form ionic interaction with the receptor models.

Crystal structure of bis-(4-allyl-2-meth-oxy-phen-yl) terephthalate.

The asymmetric unit of the title compound, C28H26O6, contains one half-mol­ecule, with the complete molecule generated by a crystallographic inversion center. The central terephthalate and meth­oxy­benzene rings are approximately perpendicular, making a dihedral angle of 80.31 (5)°. No specific directional contacts are noted in the crystal packing. The terminal vinyl group is disordered over two orientations with an occupancy ratio of 0.796 (4):0.204 (4).

Poly(vinyl alcohol) and poly(dimethylsiloxane)-based interpenetrating polymer networks via radical polymerisation

In this paper, interpenetrating polymer networks (IPNs) based on poly(vinyl alcohol) (PVA) and poly(dimethylsiloxane) with terminal vinyl groups (PDMS-vinyl) with both hydrophilic and hydrophobic features were prepared by radical reticulation. Specifically, an aqueous PVA solution was mixed with an alcoholic PDMS-vinyl solution in the presence of 2,2-dimethoxy-2-phenylacetophenone (DMPAP) and N’,N-methylenebisacrylamide (MBA) as initiating and reticulating agents, respectively, to obtain samples with the following PVA/PDMS-vinyl (w/w) compositions: 100/0, 75/25, 50/50, and 25/75. Confirmation of the IPN formation was done by a set of techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TG), differential scanning calorimetry (DSC), as well as theoretical calculations. The techniques used showed evidence of cross-linking reactions occurring in both PVA and PDMS-vinyl. Swelling experiments showed a proper balance of the resulting IPNs in swelling polar and apolar solvents, according to their composition and cross-linking. Tools of Theoretical Chemistry (Methods of Molecular Mechanics and Quantum Mechanics) were employed for the first time to investigate the cross-linking reaction between PVA and MBA and corroborate the experimental results. The PVA/PDMS IPNs showed a high capacity (up to 80 wt.%) to absorb water and may be characterised as hydrogels.

Design of a surface-immobilized 4-nitrophenol molecularly imprinted polymer via pre-grafting amino functional materials on magnetic nanoparticles

In order to resolve the low adsorption capacity of the surface molecularly imprinting methods, an approach was developed for the preparation of magnetic imprinted polymers by pre-grafting the amino functional material, 3-aminopropyltriethoxysilane (APTES), on the surface of the silica coated magnetic substrate. APTES was used for amino functionalization of the silica coated Fe3O4 nanoparticles. Amino groups were used for immobilization of the template molecules on the magnetic surface and additionally to react with the terminal vinyl groups of cross-linker, ethylene glycol dimethacrylate (EGDMA), by the Michael addition reaction. In this way, the imprinting sites of the analytes formed on the substrate were increased. The sorbent was synthesized in the presence of 4-nitrophenol (4-NP) and EGDMA as the template and cross-linker, respectively. Different parameters affecting the adsorption, such as pH, desorption solvent type and adsorption time were evaluated and optimized. The prepared magnetic molecularly imprinted polymer (MMIP) showed high adsorption capacity and proper selectivity for the template molecule. The kinetic adsorption curve indicated that 90min was sufficient to achieve the adsorption equilibrium for MMIP. The maximum adsorption capacity was 129.1mgg−1. The experiments exhibited a linear range of 10–3000μgL−1 for 4-NP with the correlation coefficient (R2) of 0.997. The results of the real sample analysis confirmed the applicability of the proposed MMIP for quantitative analysis of 4-NP in the aqueous samples.

Widely applicable metallacarborane reagents for π-conjugated systems.

The compounds [N(CH3)4][3,3'-Co(8-(p-C6H4C2H3)-1,2-C2B9H10)(1',2'-C2B9H11)], [N(CH3)4][3,3'-Co(8-(p-C6H4CHO)-1,2-C2B9H10)(1',2'-C2B9H11)], and [N(CH3)4][3,3'-Co(8-(m-C6H4CHO)-1,2-C2B9H10)(1',2'-C2B9H11)] were synthesized using an easy methodology, in very good yields and large quantities, which are important requisites to be employed as starting reagents. They have been fully characterized by elemental analysis, IR, NMR, and MALDI-TOF-MS, and the crystal structures of [N(CH3)4][3,3'-Co(8-(p-C6H4C2H3)-1,2-C2B9H10)(1',2'-C2B9H11)] and [N(CH3)4][3,3'-Co(8-(p-C6H4CHO)-1,2-C2B9H10)(1',2'-C2B9H11)] were elucidated by single-crystal X-ray diffraction. These compounds, having terminal formyl and vinyl functional groups, are suitable platforms to involve the aromatic cobaltabisdicarbollide unit into extended π-conjugated systems. It is expected that these synthons will facilitate the applicability of metallacarboranes in a wide variety of different fields, where π-conjugated systems are needed to keep electronic communication.

Synthesis, characterization, and cure kinetics analysis of high refractive index copolysiloxanes

Two kinds of high refractive index of polysiloxane compounds containing both pendent and terminal vinyl groups were successfully synthesized through a cohydrolysis-condensation method based on alkoxy silanes in the presence of acids and anionic ring-opening copolymerization of methylphenycyclosiloxane (Dn) and octamethylcyclotetrasiloxane (D4), respectively. Their structures were confirmed by Fourier-transformed infrared and nuclear magnetic resonance spectra (1H NMR and 29Si NMR). The curing kinetics of the silicone resin (MPSR) in the presence of phenylvinyl silicone oil (MPSO) as reactive diluent and T-shaped hydrosiloxane (TPHS) as crosslinking agent was studied by non-isothermal differential scanning calorimeter at different heating rates. The kinetic parameters of the curing process were determined by Friedman and Sestak–Berggren method. A comparison of the results calculated with the experimental data showed that Sestak–Berggren equation was found to be the most adequately selected to describe the cure kinetics of the studied silicone resin, and the experimental data had a great coherence with that theoretically calculated. It would give a valuable guide for the curing process of silicone resin. In addition, TG curves showed that the cured MPSR/MPSO/TPHS system exhibited much higher heat resistance and thermal stability compared to MQ resin/PMVS/PHVS blends.

Synthesis of telechelic vinyl/allyl functional siloxane copolymers with structural control

Multifunctional siloxane copolymers with terminal vinyl or allyl functional groups are synthesised through the borane-catalysed polycondensation of hydrosilanes and alkoxysilanes. Copolymers of varying molecular weights (w = 13 200–70 300 g mol−1), spatially well-distributed functional groups and high end-group fidelity are obtained in a facile and robust synthetic scheme involving polycondensation, end-group transformation and different functionalisation reactions such as Cu(I)-mediated azide–alkyne cycloaddition. Pendant alkyl chloride, alkyl azide, bromoisobutyryl, 4-nitrobenzene and 1-ethyl-imidazolium chloride fragments with programmable spatial distributions are incorporated in the copolymer backbones. NMR and FTIR spectroscopy as well as size exclusion chromatography corroborate the efficacy and versatility of this modular approach.