Electrochemically reduced tungsten‐based active species as catalysts for cross‐metathesis reactions: cross‐metathesis of non‐functionalized olefins

The electrochemical reduction of WCl₆ results in the formation of an active olefin (alkene) metathesis catalyst. The application of the WCl₆–e^?–Al–CH₂Cl₂ catalyst system to cross‐metathesis reactions of non‐functionalized acyclic olefins is reported. Undesirable reactions, such as double‐bond shift isomerization and subsequent metathesis, were not observed in these reactions. Cross‐metathesis of 7‐tetradecene with an equimolar amount of 4‐octene generated the desired cross‐product, 4‐undecene, in good yield. The reaction of 7‐tetradecene with 2‐octene, catalyzed by electrochemically reduced tungsten hexachloride, resulted in both self‐ and cross‐metathesis products. The cross‐metathesis products, 2‐nonene and 6‐tridecene, were formed in larger amounts than the self‐metathesis products of 2‐octene. The optimum catalyst/olefin ratio and reaction time were found to be 1 : 60 and 24 h, respectively. The cross‐metathesis of symmetrical olefins with α‐olefins was also studied under the predetermined conditions. Copyright © 2003 John Wiley & Sons, Ltd.     

Electrochemically reduced tungsten‐based active species as catalysts for metathesis‐related reactions: ring‐opening metathesis copolymerization of cyclopentene with cyclooctene

The ring‐opened metathesis copolymerization of cyclopentene with cyclooctene by an electrochemically generated WCl₆‐based catalyst has been prepared and ¹³C NMR spectroscopy used to analyse in detail the nature of the homo‐ and hetero‐dyad units. This copolymer was characterized by gel‐permeation chromatography (M_n = 12 900, PDI= 2.2) and differential scanning calorimetry analysis. The glass‐transition temperature T_g of the copolymer was ?18.7 °C. Homopolymerization of cyclopentene is also reported to compare with copolymers produced in this work. Copyright © 2005 John Wiley & Sons, Ltd.     

Electrochemically generated tungsten‐based active species as catalysts for metathesis‐related reactions: 1. Acyclic diene metathesis polymerization of 1,9‐decadiene

The application of the WCl₆–e^?–Al–CH₂Cl₂ system to acyclic diene metathesis polymerization of 1,9‐decadiene is reported. The polyoctenamer formed is of a weight‐average molecular weight of 9000 with a polydispersity of 1.92. IR and NMR spectral analyses indicate the retention of the double bonds in the polymer structure with high trans content as expected from a step condensation reaction. This relatively stable catalytic system, however, also activates the competing vinyl addition reactions while being inactive in ring‐closure metathesis reactions. Copyright © 2002 John Wiley & Sons, Ltd.     

Electrochemically generated tungsten‐based active species as catalysts for metathesis‐related reactions: 2. Ring‐opening metathesis polymerization of norbornene

The present work reports the application of the WCl₆–e^?–Al–CH₂Cl₂ catalyst system to the ring‐opening metathesis polymerization of norbornene. Analysis of the polynorbornene microstructure by means of ¹H and ¹³C NMR spectroscopy indicates that the polymer contains a mainly cis stereoconfiguration of the double bonds (σ_c = 0.61) and a blocky distribution (r_tr_c > 1) of cis and trans double bonds (r_tr_c = 3.37). This catalytic system is reluctant to facilitate the competing addition reactions of cycloalkenes while proceeding with the polymerization reactions with good conversions and at short periods. Copyright © 2004 John Wiley & Sons, Ltd.     

Oxygen‐chelated indenylidene ruthenium catalysts for olefin metathesis

Olefin metathesis is a transition metal‐mediated transformation that rearranges the carbon atoms of the carbon–carbon double bond of olefins. This reaction has become one of the most important and powerful reactions. Therefore development of new, well‐defined, highly active and selective catalysts is very desirable and a valuable goal. This mini‐review mainly introduces the development of ruthenium catalysts in olefin metathesis highlighting oxygen‐chelated indenylidene ruthenium catalysts. Applying an alkoxyl group on the indenylidene ligand fragment can generate the Ru ? O chelating bond. Additionally, various modifications of the ligand as well as the catalytic activity for ring‐closing metathesis reaction and selectivity of cross metathesis reaction are overviewed. Finally, the perspectives on the development of new catalysts are summarized. Copyright © 2015 John Wiley & Sons, Ltd.     

Ring‐opening metathesis polymerization of cyclododecene using an electrochemically reduced tungsten‐based catalyst

The ring‐opening metathesis polymerization of cyclododecene using an electrochemically reduced tungsten‐based catalyst (WCl₆? e^?? Al? CH₂Cl₂) is described. In addition, the influence of reaction conditions on the polymerization yield was determined. The resulting polymer has been characterized by NMR, IR, gel permeation chromatography and differential scanning calorimetry. The glass transition temperature and melting point of the polydodecenamer are 19.6°C and 70.0°C respectively. Furthermore, cyclododecene has been polymerized into a low‐molecular‐weight polymer (12.0 × 10³) with a polydispersity of 2.06 in high yields (94%). IR and NMR analysis indicate that the polydodecenamer has a high trans content (60%). Copyright © 2004 John Wiley & Sons, Ltd.     

Cross‐metathesis functionalized exo‐olefin derivatives of lactide

Poly(lactic acid) is at the forefront of research into alternative replacements to fossil fuel derived polymers, yet preparation of derivatives of this key biodegradable polymer remain challenging. This article explores the use of two derivatives of lactide, each of which features an exocyclic olefin, and their pre‐polymerization modification by olefin cross‐metathesis. Methylenation of lactide with Tebbe's reagent generates a novel 5‐methylenated lactide monomer, (3S,6S)‐3,6‐dimethyl‐5‐methylene‐1,4‐dioxan‐2‐one, complementing the previously reported 3‐methylenated (6S)‐3‐methylene‐6‐methyl‐1,4‐dioxan‐2,5‐dione. While ring‐opening of each monomer is not productive, olefin cross‐metathesis can be used to functionalize each of the exocyclic olefins to produce a family of monomers. The ring‐opening polymerization of these new monomers, and their hydrogenated congeners, is facilitated by organo‐ and Lewis‐acid catalysts. Together, they offer a new strategy for derivatizing and altering the properties of poly(lactic acid). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 741–748     

Z‐Selective Cross Metathesis with Ruthenium Catalysts: Synthetic Applications and Mechanistic Implications

Olefin cross metathesis is a particularly powerful transformation that has been exploited extensively for the formation of complex products. Until recently, however, constructing Z‐olefins using this methodology was not possible. With the discovery and development of three families of ruthenium‐based Z‐selective catalysts, the formation of Z‐olefins using metathesis is now not only possible but becoming increasingly prevalent in the literature. In particular, ruthenium complexes containing cyclometalated NHC architectures developed in our group have been shown to catalyze various cross metathesis reactions with high activity and, in most cases, near perfect selectivity for the Z‐isomer. The types of cross metathesis reactions investigated thus far are presented here and explored in depth.     

Synthesis of bio‐based internal and external cross‐linkers based on tannic acid for preparation of antibacterial superabsorbents

Recent researches focus on the synthesis of new cross‐linkers from natural resources. In the current work, functionalized tannic acid was employed as a replacement of petroleum‐based cross‐linkers because of its outstanding biochemical properties. Alkene‐ and epoxy‐functionalized tannic acids were synthesized as internal and external cross‐linkers, respectively. Cross‐linker structures were characterized with Ft‐IR and ¹HNMR analysis. Different amounts, as well as different numbers of alkene functional group, were incorporated during the superabsorbent synthesis. Moreover, the internal cross‐linked superabsorbent was surface cross‐linked with different amounts of epoxy‐functionalized tannic acid and increased the absorbency under load about 10 g g^?1. Free absorption properties in water and saline solution, absorbency under load, and rheological properties of superabsorbents were investigated. In addition, the antibacterial activity of the internal and external cross‐linked superabsorbent was studied against Escherichia coli and Staphylococcus aureus bacteria via different methods and compared with that of conventional superabsorbent.     

Ring‐opening metathesis polymerization of amino acid‐functionalized norbornene derivatives

Amino acid‐derived novel norbornene derivatives, N,N′‐(endo‐bicyclo[2.2.1] hept‐5‐en‐2,3‐diyldicarbonyl) bis‐L ‐alanine methyl ester (NBA), N,N′‐(endo‐bicyclo[2.2.1]hept‐5‐en‐2,3‐diyldicarbonyl) bis‐L ‐leucine methyl ester (NBL), N,N′‐(endo‐bicyclo[2.2.1]hept‐5‐en‐2,3‐diyldicarbonyl) bis‐L ‐phenylalanine methyl ester (NBF) were synthesized and polymerized using the Grubbs 2nd generation ruthenium (Ru) catalyst. Although NBA, NBL, and NBF did not undergo homopolymerization, they underwent copolymerization with norbornene (NB) to give the copolymers with M_n ranging from 5200 to 38,100. The maximum incorporation ratio of the amino acid‐based unit was 9%, and the cis contents of the main chain were 54–66%. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5337–5343, 2006     

Total Synthesis of (+)‐Cryptocaryalactone and of a Diastereoisomer of (+)‐Strictifolione via Ring‐Closing Metathesis (RCM) and Olefin Cross‐Metathesis (CM)

Ring‐closing metathesis (RCM) and olefin cross‐metathesis (CM) reactions were used as the key steps for the synthesis of (+)‐cryptocaryalactone ( 1 ) and the first synthesis of the diastereoisomer 3 of (+)‐strictifolione, starting from the commercially available L ‐malic acid (=(2S)‐2‐hydroxybutanedioic acid).     

Synthesis of high molecular weight trans‐poly(9,9‐di‐n‐octylfluorene‐2,7‐vinylene) by the acyclic diene metathesis polymerization using molybdenum catalysts

High molecular weight trans‐poly(9,9‐di‐n‐octylfluorene‐2,7‐vinylene) was prepared under reduced pressure in the presence of a well‐defined Schrock‐type catalyst, Mo(CHCMe₂Ph)(N‐2,6‐Me₂C₆H₃)[OCMe(CF₃)₂]₂, in toluene. The effect of initial monomer concentration was found to be an important factor for preparing high molecular weight polymers with unimodal molecular weight distributions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2463–2470, 2001     

Synthesis of poly(3‐hexylthiophene)‐block‐poly(ethylene)‐block‐poly(3‐hexylthiophene) via a combination of ring‐opening olefin metathesis polymerization and grignard metathesis polymerization

Novel rod–coil–rod ABA triblock copolymers, poly(3‐hexylthiophene)‐block‐poly(ethylene)‐block‐poly(3‐hexylthiophene) (P3HT‐b‐PE‐b‐P3HT) were synthesized by using a combination of a Ru‐catalyzed ring‐opening metathesis polymerization of 1,4‐cyclooctadiene in the presence of a suitable chain transfer agent (CTA) and a Ni‐catalyzed Grignard metathesis polymerization of 5‐chloromagnesio‐2‐bromo‐3‐hexylthiophene followed by hydrogenation. Using this methodology, the molecular weights of the poly(butadiene) (PBD) or the P3HT blocks were controlled by adjusting the initial monomer/CTA or the initial monomer/macroinitiator ratio, respectively. In addition, the triblock structure was confirmed by selective oxidative degradation of the PBD block found in the intermediate P3HT‐b‐PBD‐b‐P3HT copolymer produced in the aforementioned method, followed by analysis of the degradation products. Thermal analysis and atomic force microscopy of P3HT‐b‐PE‐b‐P3HT revealed that the material underwent phase separation in the solid state, a feature which may prove useful for improving charge mobilities within electronic devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3810–3817     

Synthesis of highly thermostable norbornene‐isoprene‐1‐octene terpolymer with titanium catalyst

Terpolymerization of norbornene (NB), isoprene (IP), and 1‐octene was achieved by using fluorenylamido‐ligated titanium catalyst, which showed very high activity for the copolymerization of NB and various α‐olefins. The content of IP in the terpolymer was controlled by the feed ratio and reaction temperature up to 7 mol %. The incorporated IP was mainly inserted in 1,4‐addition. The polymer was dissolved into common solvents such as toluene and chloroform, which enabled the preparation of a transparent film by solution casting process. The degradation temperature of the terpolymer was comparable with other cyclic olefin copolymers and the glass transition temperature (T_g) was higher than that of NB‐1‐octene copolymer with almost the same NB content. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2136–2140     

Synthesis and Evaluation of Ruthenium 2‐Alkyl‐6‐mercaptophenolate Catalysts for Olefin Metathesis

A series of ruthenium carbene catalysts containing 2‐sulfidophenolate bidentate ligand with an ortho‐substituent next to the oxygen atom were synthesized. The molecular structure of ruthenium carbene complex containing 2‐isopropyl‐6‐sulfidophenolate ligand was confirmed through single crystal X‐ray diffraction. An oxygen atom can be found in the opposite position of the N‐heterocyclic carbene (NHC) based on the steric hindrance and strong trans‐effects of the NHC ligand. The ruthenium carbene catalyst can catalyze ring‐opening metathesis polymerization (ROMP) reaction of norbornene with high activity and Z‐selectivity and cross metathesis (CM) reactions of terminal alkenes with (Z)‐but‐2‐ene‐1,4‐diol to give Z‐olefin products (Z/E ratios, 70:30–89:11) in low yields (13%–38%). When AlCl₃ was added into the CM reactions, yields (51%–88%) were considerably improved and process becomes highly selective for E‐olefin products (E/Z ratios, 79:21–96:4). Similar to other ruthenium carbene catalysts, these new complexes can tolerate different functional groups.     

Highly stable magnetically separable copper nanocatalyst as an efficient catalyst for C(sp2)–C(sp) and C(sp2)–C(sp2) cross‐coupling reactions

A copper catalyst has been explored as an efficient and recyclable catalyst to effect Sonogashira and Suzuki cross‐coupling reactions. After modification of 2‐(((piperazin‐1‐ylmethyl)imino)methyl)phenol (PP) on the surface of amorphous silica‐coated iron oxide (Fe₃O₄@SiO₂@Cl) magnetic core–shell nanocomposite, copper(II) chloride was employed to synthesize the Fe₃O₄@SiO₂@PP‐Cu catalyst, affording a copper loading of 1.52 mmol g⁻¹. High yield, low reaction times, non‐toxicity and recyclability of the catalyst are the main merits of this protocol. The catalyst was characterized using Fourier transform infrared, X‐ray photoelectron, energy‐dispersive X‐ray and inductively coupled plasma optical emission spectroscopies, X‐ray diffraction, scanning and transmission electron microscopies, and vibrating sample magnetometry.     

Highly selective oxidative cross‐coupling polymerization with copper(I)‐bisoxazoline catalysts

The asymmetric oxidative coupling polymerization of methyl 6,6′‐dihydroxy‐2,2′‐binaphthalene‐7‐carboxylate with the copper‐diamine catalysts under an O₂ atmosphere was carried out. As is the case with the CuCl‐2,2′‐(S)‐isopropylidenbis(4‐phenyl‐2‐oxazoline) [(S)IPhO] catalyst, a polymer with a high cross‐coupling selectivity of 96% was obtained in 71% yield, whose THF‐soluble part had a number‐average molecular weight of 4.5 × 10³. To estimate the enantioselectivity with respect to the cross‐coupling linkage in the obtained polymer, the model asymmetric oxidative cross‐coupling reaction with CuCl‐(S)IPhO was also conducted, and the products showed a 94% cross‐coupling selectivity and enantioselectivity of 31% ee (S). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6287–6294, 2005     

Methionine: a green and efficient promoter for copper‐catalyzed Sonogashira cross‐coupling reactions

In the presence of amino acids as environmentally friendly ligands, CuI‐catalyzed Sonogashira cross‐coupling of various aryl halides with phenylacetylene was conducted to afford the corresponding internal alkynes. l ‐Methionine was found to be useful for this palladium‐free and amine‐free coupling reaction. It was also found that the solvent system plays an important role in this reaction, and significantly affects the product formation and reaction rate. Sonogashira coupling of aryl iodides and aryl bromides in dimethylsulfoxide or dimethylformamide gave the coupled products in good to excellent yields. Copyright © 2015 John Wiley & Sons, Ltd.