Structurally diverse polyamides obtained from monomers derived via the ugi multicomponent reaction

The combination of the Ugi four-component reaction (Ugi-4CR) with acyclic diene metathesis (ADMET) or thiol-ene polymerization led to the formation of poly-1-(alkylcarbamoyl) carboxamides, a new class of substituted polyamides with amide moieties in the polymer backbone, as well as its side chains. 10-Undecenoic acid, obtained by pyrolysis of ricinoleic acid, the main fatty acid of castor oil, was used as the key renewable building block. The use of different primary amines, as well as isonitriles (isocyanides) for the described Ugi reactions provided monomers with high structural diversity. Furthermore, the possibility of versatile post-modification of functional groups in the side chains of the corresponding polymers should be of considerable interest in materials science. The obtained monomers were polymerized by ADMET, as well as thiol-ene, chemistry and all polymers were fully characterized. Finally, ortho-nitrobenzylamide-containing polyamides obtained by this route were shown to be photoresponsive and exhibited a dramatic change of their properties upon irradiation with light.     

Synthesis and characterization of a chlorofunctionalized unsaturated carbosilane oligomer

Acyclic diene metathesis (ADMET) polymerization offers a viable route for the synthesis of chlorofunctionalized unsaturated carbosilane oligomers. The Si Cl bond in unsaturated carbosilane monomers remains inert during metathesis and the use of a highly reactive molybdenum-based, Lewis acid-free alkylidene catalyst affords unsaturated chlorofunctionalized carbosilane oligomers with known vinyl end groups. The first synthesis of an unsaturated carbosilane oligomer functionalized with a Si Cl bond was performed. A chlorofunctionalized silacyclopentene product was also observed, due to a backbiting reaction. This new class of functionalized oligomers has a low glass transition temperature and sites of unsaturation which may be used for further reaction. ADMET chemistry now provides access to a variety of chlorofunctionalized unsaturated carbosilanes which can be used to tailor make hydrolytically stable carbosilane oligomers and polymers via nucleophilic grafting reactions.     

Graft copolymers by acyclic diene metathesis and atom transfer radical polymerization techniques

Precise graft copolymer architectures were achieved by combining the macromonomer technique with the acyclic diene metathesis (ADMET) reaction. These well‐defined copolymer structures were the result of proper monomer design before metathesis polymerization. Features such as length of the graft, nature, and concentration of the graft site along the backbone were manipulated via the combination of living atom transfer radical polymerization methods with ADMET chemistry. Furthermore, the physical behavior of these materials was altered such that they presented dissimilar thermal properties of either the homopolymers or random copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2816–2827, 2003     

Carbosilane/carbosiloxane‐based ADMET homopolymers and copolymers possessing latent reactivity

Reactive methoxy‐functionalized carbosilane and carbosiloxane dienes can be either homopolymerized or copolymerized via acyclic diene metathesis (ADMET) polycondensation chemistry to produce reactive materials with mechanical behavior dependent on the molar ratios of the comonomers. The methoxy‐functional group within the polycarbosilane repeat unit remains inert during the metathesis polymerization and can be triggered subsequently with water to generate crosslinks between polymer chains. In this way, linear, thermoplastic copolymers can be prepared with ADMET chemistry and converted into crosslinked, thermoset copolymers upon exposure to moisture. Crosslinked films containing 5–10% of the crosslinked hard segment are soft and flexible materials. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1544–1550, 2000     

ADMET: Metathesis polycondensation

Although it is well known that Acyclic Diene METathesis (ADMET) describes an olefin metathesis polymerization mode that relies on double‐bond substituent interchange of a diolefin, the story behind its discovery is not. The story is divulged here. Olefin metathesis has a rich history dating to the 1950s, but the one particular metathesis mode mentioned, ADMET, has more recent historical roots. ADMET polymerization is easy to do and highlighted here are the particular reaction details for success. Additionally, the most recent advances from the past 5 years are detailed, exemplifying this reaction's wide utility from fundamental structure–property studies to multiple advanced applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Recent developments in olefin cross-metathesis

Among the many types of transition-metal-catalyzed C-C bond-forming reactions, olefin metathesis has come to the fore in recent years owing to the wide range of transformations that are possible with commercially available and easily handled catalysts. Consequently, olefin metathesis is now widely considered as one of the most powerful synthetic tools in organic chemistry. Until recently the intermolecular variant of this reaction, cross-metathesis, had been neglected despite its potential. With the evolution of new catalysts, the selectivity, efficiency, and functional-group compatibility of this reaction have improved to a level that was unimaginable just a few years ago. These advances, together with a better understanding of the mechanism and catalyst-substrate interactions, have brought us to a stage where more and more researchers are employing cross-metathesis reactions in multistep procedures and in the synthesis of natural products. The recent inclusion of alkynes and hindered bicyclic olefins as viable substrates for bimolecular metathesis coupling, the discovery of enantioselective cross-metathesis and cross-metathesis in water, and the successful marriage of metathesis and solid-phase organic synthesis has further widened the scope of this versatile reaction.     

Transformation reactions involving metathesis polymerisation

Transformation reactions provide a facile route to synthesise block copolymers that cannot be made from a single polymerisation mode. A variety of transformation reactions involving free radical, cationic, anionic, group transfer, Ziegler–Natta and metathesis are known. In this article, transformation reaction involving metathesis polymerisation is reviewed.     

Modeling random methyl branching in ethylene/ propylene copolymers using metathesis chemistry: synthesis and thermal behavior

The structure of random ethylene/propylene (EP) copolymers has been modeled using step polymerization chemistry. Six ethylene/propylene model copolymers have been prepared via acyclic diene metathesis (ADMET) polymerization and characterized for primary and higher level structure using in-depth NMR, IR, DSC, WAXD, and GPC analysis. These copolymers possess 1.5, 7.1, 13.6, 25.0, 43.3, and 55.6 methyl branches per 1000 carbons. Examination of these macromolecules by IR and WAXD analysis has demonstrated the first hexagonal phase in EP copolymers containing high ethylene content (90%) without the influence of sample manipulation (temperature, pressure, or radiation). Thermal behavior studies have shown that the melting point and heat of fusion decrease as the branch content increases. Further, comparisons have been made between these random ADMET EP copolymers, random EP copolymers made by typical chain addition techniques, and precisely branched ADMET EP copolymers.     

Understanding the effect of allylic methyls in olefin cross-metathesis

A series of NMR spectroscopy experiments have been conducted with both the model compound, 3-methyl-1-pentene and the corresponding ADMET monomer 3,6,9-trimethylundeca-1,10-diene (11) to better understand the effect of allylic methyls during olefin metathesis chemistry. Traditional ADMET catalysts such as Schrock’s molybdenum (1), and Grubbs’ ruthenium 1st and 2nd generation (2 and 3) were examined under cross-metathesis and ADMET conditions. Regardless of catalyst selection, 50% or less metathesis conversion was observed for all reactions, especially in the case of the more sterically encumbered diene. With Schrock’s molybdenum catalyst 1, the reaction leads to an accumulation of the non-productive metallacyclobutane, trapping the catalyst in an inactive form. With Grubbs’ ruthenium catalysts 2 and 3, the substrate coordinates to the metal center primarily to yield non-productive metathesis, which results in a build-up of the methylidene complex leading to catalyst decomposition. These results are directly correlated to the orientation of the substrate’s bulk during the metallacyclobutane formation, the alkyl branch being adjacent to the metal center in the case of the molybdenum catalyst 1, and opposite to it in the case of ruthenium catalyst 2 and 3.     

A new synthetic approach to phenol derivatives: use of ring-closing olefin metathesis

Phenol derivatives, which are one of the most important classes of aromatic compounds in organic chemistry, were synthesized by ruthenium-catalyzed ring-closing olefin metathesis (RCM) of 1,4,7-trien-3-ones with versatile substitution patterns. The RCM reaction for producing phenol derivatives was also successful with 1,5,7-trien-3-one as another precursor. Most of the phenols prepared here could not be obtained easily by conventional methods.     

Alkene Metathesis – A Tool for the Synthesis of Conjugated Polymers

Alkene metathesis is a superb methodology. We report the progress using alkene metathesis in the synthesis of polymeric organic semiconductors. Three classes of polymers have been synthesized using acyclic diene metathesis (ADMET) or ring opening metathesis polymerization (ROMP), viz., poly(acetylene)s (PA), poly(arylene‐vinylene)s (PAV), and organometallic polymers. For PAs, ROMP of cyclooctatetraenes is best, whereas for PAV, both ADMET and indirect and direct ROMP are viable. Metathesis performs flawlessly with the correct monomers, as molybdenum and particularly the robust Ru carbenes demonstrate. When performing ROMP, one is often rewarded with structurally uniform polymers that can display very low polydispersities. Overall, metathesis is a powerful tool for the preparation of semiconducting polymers.     

Surface Modification Based on Diselenide Dynamic Chemistry: Towards Liquid Motion and Surface Bioconjugation

Surface modification is an important technique in fields, such as, self‐cleaning, surface patterning, sensing, and detection. The diselenide bond was shown to be a dynamic covalent bond that can undergo a diselenide metathesis reaction simply under visible light irradiation. Herein we develop this diselenide dynamic chemistry into a versatile surface modification method with a fast response and reversibility. The diselenide bond could be modified onto various substrates, such as, PDMS, quartz, and ITO conductive film glass. Different functional diselenide molecules could then be immobilized onto the surface via diselenide metathesis reaction. We demonstrated that by using this modification method we could achieve liquid motion in a capillary tube under light illumination. We also show that this approach has the potential to serve as an efficient modification method for surface bioconjugation, which has practical applications in clinical usage.     

Fatty acid derived phosphorus‐containing polyesters via acyclic diene metathesis polymerization

The acyclic diene metathesis (ADMET) polymerization of a phosphorus‐containing α,ω‐diene prepared from a plant oil derived building block is reported. Different ruthenium based metathesis catalysts and conditions were tested to optimize the ADMET polymerization of this monomer. Undecylenyl undecenoate was used as fully renewable comonomer to obtain polyesters with different phosphorus contents and to increase the renewable content of the final polymers. Copolymerization caused marked variations in the molecular weights leading to polyesters from 6 to 38 KDa. The effect of the ADMET polymerization temperature in the thermal properties of the copolymers was studied and their thermal degradation and flame retardant properties were evaluated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5760–5771, 2009     

Iron-Catalyzed Olefin Metathesis: Recent Theoretical and Experimental Advances

The “metathesis reaction” is a straightforward and often metal-catalyzed chemical reaction that transforms two hydrocarbon molecules to two new hydrocarbons by exchange of molecular fragments. Alkane, alkene and alkyne metathesis have become an important tool in synthetic chemistry and have provided access to complex organic structures. Since the discovery of industrial olefin metathesis in the 1960s, many modifications have been reported; thus, increasing scope and improving reaction selectivity. Olefin metathesis catalysts based on high-valent group six elements or Ru(IV) have been developed and improved through ligand modifications. In addition, significant effort was invested to realize olefin metathesis with a non-toxic, bio-compatible and one of the most abundant elements in the earth′s crust; namely, iron. First evidences suggest that low-valent Fe(II) complexes are active in olefin metathesis. Although the latter has not been unambiguously established, this review summarizes the key advances in the field and aims to guide through the challenges.     

2005年诺贝尔化学奖成果简介

2005年诺贝尔化学奖授予在烯烃复分解合成转换方面做出重要贡献的3位科学家:Y ves Chauvin,Richard R.Schrock和Robert H.Grubbs.简要介绍了3位获奖者的主要贡献,烯烃复分解反应的分类和催化反应机理,金属卡宾催化剂及烯烃复分解反应的一些应用.另外,介绍了此领域目前研究的主要科学问题.     

Exploring new synthetic strategies in the development of a chemically activated Ru-based olefin metathesis catalyst

The objective of this work was to develop an industrially relevant olefin metathesis initiator, which circumvents the expensive, patent protected, often cumbersome preparative routes via Grubbs benzylidene complexes. Upon coordination of a Schiff base ligand to a second-generation ruthenium allenylidene complex, the formation of three catalyst isomers was observed. The major isomer was successfully isolated, and tested in a few olefin metathesis reactions. Acids such as HCl and HSiCl(3) were found to boost the metathesis reaction but the in situ formation of a neutral Ru carbyne complex restricted the catalytic capacity. Using the Lewis acid PhSiCl(3), the formation of a carbyne species was avoided, and turnover numbers up to 30,000 were reached in the ring-opening metathesis polymerisation of cycloocta-1,5-diene.     

Synthesis of Poly(arylene vinylene)s with Different End Groups by Combining Acyclic Diene Metathesis Polymerization with Wittig‐type Couplings

A series of end‐functionalized poly(9,9′‐di‐n ‐octylfluorene vinylene)s (EF‐PFVs) with different end groups were obtained by 1) synthesizing EF‐PFV with vinyl end groups by acyclic diene metathesis (ADMET) polymerization with a molybdenum catalyst and termination with an aldehyde and 2) subsequent olefin metathesis of the vinyl group with the molybdenum catalyst followed by Wittig‐type coupling with another aldehyde. The exclusive formation of EF‐PFVs containing a vinyl end group by the ADMET polymerization was confirmed by grafting PEG, and by the synthesis of amphiphilic triblock copolymers by combining atom transfer radical polymerization from the PFV chain end with PEG grafting through a click reaction. Various EF‐PFVs with different end groups, such as C₆F₅, pyridyl, ferrocenyl, and terthiophene, have thus been prepared. Their fluorescence spectra (e.g., intensities, emission wavelengths) were influenced by the end groups and the length of the conjugation.     

Novel ABC miktoarm star terpolyphosphoesters: Facile construction and high‐flame retardant property

A combination of ring‐opening metathesis polymerization (ROMP), ring‐opening polymerization (ROP), and acyclic diene metathesis (ADMET) polymerization approach was first time utilized in the preparation of novel ABC miktoarm star terpolyphosphoesters (PPEs). Acrylate‐terminated monotelechelic PPE was first prepared through ROMP of 7‐membered cyclic phosphate monomer in the presence of a terminating agent, and then terminal acrylate group was readily converted, by thiol‐Michael addition click reaction and esterification, to a heterodifunctional PPE with hydroxyl and acrylate groups, which was a key precursor for the preparation of ABC miktoarm terpolymers. ROP of the cyclic phosphoester monomer initiated by this PPE was successively carried out to generate the acrylate‐functionalized block PPE, which utilized as a selective macromolecular chain stopper in subsequent ADMET polymerization of α,ω‐diene phosphate monomer, finally producing miktoarm terpolyphosphoester. These prepared miktoarm star terpolyphosphoesters demonstrated superior thermal and flame retardant properties via TGA, limiting oxygen index, and microscale combustion calorimetry tests. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 692–701     

Ring-closing metathesis: novel routes to aromatic heterocycles

Olefin metathesis has been established as an important and general reaction in synthetic organic chemistry. Recently, it has attracted interest as a powerful tool for the construction of aromatic heterocycles. The importance of heteroaromatic motifs in medicinal chemistry and biology, as well as the efficiency and wealth of metathesis transformations, have resulted in significant success in this rapidly developing area.     

Precision ADMET polyolefins containing dithiane: Synthesis,thermal properties,and macromolecular transformation

1,3‐Dithiane and its derivatives are widely used as powerful acyl anion equivalent to a range of useful transformations that are needed in the synthesis of natural products. In this work, a series of polyolefins containing pendant dithiane groups have been designed and synthesized via acyclic diene metathesis polymerization (ADMET) polymerization and subsequent hydrogenation. The structures of these polymers were characterized by ¹H NMR, ¹³C NMR, and FT‐IR, and successful incorporation of the dithiane groups was proved. With different contents of the dithiane moieties, these ADMET polymers exhibited distinct thermal properties different from each other as evidenced by differential scanning calorimetry and thermal gravimetric analysis. The dithiane units in the ADMET polymer with 20 methylene carbons between the adjacent dithiane groups were transformed into thiol groups via reaction with Bu₃SnH. This work provided a convenient route to synthesize polyethylene with pendant thiol groups that are evenly distributed in the chain. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2468–2475