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Acyclic diene metathesis (ADMET) polymerization. Synthesis of unsaturated polyethers
Abstract
Previously unknown unsaturated polyethers from acyclic, ether-containing dienes have first been obtained via acyclic diene metathesis (ADMET) polymerization in the presence of the catalyst W(CH-t-Bu)(N-2,6-C6H3-i-Pr2)[OCMe(CF3)2]2. Polymer yields are high, and number-average molecular weights up to M(n)BAR = 15 000-18 000 are observed. Structural assignments of the polymers are based on C-13 NMR and H-1 NMR spectroscopy, IR spectroscopy, and elemental analysis. The polymerizability of the ether-containing alpha,omega-diene appears to be a function of the distance between the ether oxygen and the metathesizing double bond in the monomer. An ether-containing diene has also been copolymerized with 1,9-decadiene.
... Here, we demonstrate the concept of mechanochemically regulating T c with the 2,5-dihydrofuran (DHF) system, the ring-opening metathesis polymerization (ROMP) of which has proved challenging 13 . We designed a polymer P1 (Fig. 1b), which is an unsaturated polyether containing cyclobutane-fused THF in each repeat unit. ...
... For example, Höcker's attempts to polymerize DHF in bulk with a tungsten catalyst and with a chromium catalyst both failed 19 . Wagener reported the bulk ROMP of DHF using a molybdenum catalyst that yielded PDHF with a number-average molecular weight (M n ) >20 kDa, but the conversion was only 33% 13 . In addition, their acyclic diene metathesis polymerization using diallyl ether as the monomer afforded DHF and PDHF at conversions of 63% and 37%, respectively, and the latter had a M n of 640 13 . ...
... Wagener reported the bulk ROMP of DHF using a molybdenum catalyst that yielded PDHF with a number-average molecular weight (M n ) >20 kDa, but the conversion was only 33% 13 . In addition, their acyclic diene metathesis polymerization using diallyl ether as the monomer afforded DHF and PDHF at conversions of 63% and 37%, respectively, and the latter had a M n of 640 13 . Compared to cyclopentene and 2,3-dihydrofuran, the difficulty in the ROMP of DHF can be attributed to its even lower RSE ( Fig. 2a; RSEs were calculated according to a previously described procedure 17,21 ). ...
Polymers with low ceiling temperatures (Tc) are highly desirable as they can depolymerize under mild conditions, but they typically suffer from demanding synthetic conditions and poor stability. We envision that this challenge can be addressed by developing high-Tc polymers that can be converted into low-Tc polymers on demand. Here, we demonstrate the mechanochemical generation of a low-Tc polymer, poly(2,5-dihydrofuran) (PDHF), from an unsaturated polyether that contains cyclobutane-fused THF in each repeat unit. Upon mechanically induced cycloreversion of cyclobutane, each repeat unit generates three repeat units of PDHF. The resulting PDHF completely depolymerizes into 2,5-dihydrofuran in the presence of a ruthenium catalyst. The mechanochemical generation of the otherwise difficult-to-synthesize PDHF highlights the power of polymer mechanochemistry in accessing elusive structures. The concept of mechanochemically regulating the Tc of polymers can be applied to develop next-generation sustainable plastics. Polymers with low ceiling temperatures (Tc) are highly desirable as they can depolymerize under mild conditions, but they typically suffer from demanding synthetic conditions and poor stability. Here, the authors envision that this challenge can be addressed by developing high-Tc polymers that can be converted into low-Tc polymers on demand.
... This polymerization method can be used to give a different kinds of polymers and polymer architectures that cannot be accomplished with other polymerization methods. Different kinds of polymers, such as unsaturated poly[carbo(dimethyl)silanes] [16], unsaturated polyethers [17][18][19], hydrocarbons [20], unsaturated polycarbonates [21], unsaturated polyamines [22], unsaturated polyacetals [23], organoboronates [24], carbosilane-/carbosiloxane-based homopolymers/copolymers [25], and unsaturated polyesters [26] were prepared by the Wagener group. Most of the polymers, which were synthesized using ADMET polymerization, were optically inactive polymers. ...
... These squaramides are chiral dienes and they amenable to ADMET polymerization. A variety of diene compounds has been polymerized under the ADMET reaction condition to afford the polymers [15][16][17][18][19][20][21][22]. We synthesized the chiral polymers by repetitive ADMET reactions of 1-3. ...
Under the acyclic diene metathesis (ADMET) reaction condition, the C3-vinyl groups of cinchona alkaloids readily react with each other to form a C-C bond. A novel type of cinchona alkaloid polymers was synthesized from dimeric cinchona squaramides using the Hoveyda-Grubbs’ second-generation catalysts (HG2) by means of ADMET reaction. The chiral polymers, containing cinchona squaramide moieties in their main chains, were subsequently employed as catalysts for the enantioselective Michael reaction to give the corresponding chiral adducts in high yields with excellent enantioselectivity and diastereoselectivity. Both enantiomers from the asymmetric Michael reaction were distinctively prepared while using the polymeric catalysts, possessing pseudoenantiomeric structures. The catalysts were readily recovered from the reaction mixture and recycled several times due to the insolubility of the cinchona-based squaramide polymers.
... The phenomenon has become known as the "negative neighboring group effect" [28]. In the first attempts to polymerize ester-and ether-containing monomers by ADMET it was observed that at least two methylene spacers from the carbonyl side of the ester were required for successful polymerization, presumably because the electrons on the oxygen would coordinate to the metal center during metathesis and inhibit the catalyst [29,30]. This behavior has been observed for a variety of ADMET monomers containing coordinating functional groups such as esters [30], ethers [29], carbonate esters [31], thioethers [32], amines [33], silanes and siloxanes [34], sulfonic esters [35], phosphoesters [36]. ...
... In the first attempts to polymerize ester-and ether-containing monomers by ADMET it was observed that at least two methylene spacers from the carbonyl side of the ester were required for successful polymerization, presumably because the electrons on the oxygen would coordinate to the metal center during metathesis and inhibit the catalyst [29,30]. This behavior has been observed for a variety of ADMET monomers containing coordinating functional groups such as esters [30], ethers [29], carbonate esters [31], thioethers [32], amines [33], silanes and siloxanes [34], sulfonic esters [35], phosphoesters [36]. ...
Acyclic Diene Metathesis (ADMET) polymerization was established decades ago and has since developed into a robust and reliable technique. A wide range of different, new materials exhibiting unique properties has been produced via ADMET polymerization since its development. This versatile technique allows, through the right combination of monomer design and choice of catalyst, the synthesis of various functional polymers in addition to a precise control over primary structure. Systematic studies on precise ADMET polymers have greatly contributed to a better understanding of how branch identity and its distribution along the polymer backbone affect the thermal/electronic properties, crystallization, molecular dynamics and morphology of different materials. This article presents an extensive review of how ADMET started, the mechanism that underlies the structural features of ADMET polymers and the different strategies and techniques that have been developed over the years to overcome common synthetic challenges. Monomer synthesis methods are also discussed in detail, providing an important overview of the limitations and advantages of using ADMET as a polymerization technique. Many examples are given of functional ADMET polymers that have been developed by research groups all over the world.
... 含醚基的对称α,ω-二烯是第一个通过ADMET聚 合方法成功聚合的功能化二烯单体 [37] . 然而, 当采用 Schrock型催化剂时, 要实现含醚基的二烯ADMET聚 合, 氧原子和末端烯烃之间至少需要间隔三个亚甲基. ...
... Capitalizing on the inexpensive and readily available cis-hex-4-en-1-ol and cis-oct-5-en-1-ol, a variety of monomers were synthesized in one or two steps in high yields (see Fig. 2a and 'General procedure A' to 'General Procedure E' in the Supplementary Information) [33][34][35][36] . These two groups of monomers (1-4 and 5-8) were selected to interrogate the all-cis poly(p-phenylene vinylene)s (PPVs) with living characteristics and unusually high molar masses 23,24 . ...
The cis/trans geometry of olefins is known to dramatically influence the thermal and mechanical properties of polyalkenamers. Yet, polymerization methods that efficiently control this parameter are scarce. Here we report the development of a stereoretentive acyclic diene metathesis polymerization that uses the reactivity of dithiolate Ru carbenes combined with cis monomers. These Ru catalysts exhibit exquisite retention of the cis geometry and tolerate many polar functional groups, enabling the synthesis of all-cis polyesters, polycarbonates, polyethers and polysulfites. The stereoretentive acyclic diene metathesis polymerization is also characterized by low catalyst loadings and tolerance towards trans impurities in the monomer batch, which should facilitate large-scale implementation. Modulation of the reaction temperature and time leads to an erosion of stereoretention, permitting a stereocontrolled synthesis of polyalkenamers with predictable cis:trans ratios. The impact of the stereochemistry of the repeating alkenes on the thermal properties is clearly demonstrated through differential scanning calorimetry and thermogravimetric analysis.
... In principle, there are some requirements for the structure of the symmetrical diene monomers: (i) if the number of methylene groups between functional group and the terminal double bond are less than two, polymerization will not be easy to take place due to the so-called "negative neighbouring group effect" [44]. The short distance between the functional group and terminal double bond may facilitate the coordination between functional group and the centre metal of catalyst, and therefore affect the intermediate formation and hinder the polymerization; (ii) if there is a alkyl substitution on the allyl structure, it may also hinder the formation of cyclobutane intermediates [45,46]. Therefore, the structure design of monomers is particularly important, which is directly related to the ADMET process. ...
Since the discovery of acyclic diene metathesis (ADMET), researchers have gradually developed ADMET polymerization into a mature methodology for the preparation of versatile polymers with various precise functional groups. As a representative stepwise polymerization method, ADMET enable the polymerization of relatively “inert” acyclic diene monomers. By rational design of monomer structures, the resulted functional materials can be used in various fields such as biomedicine, optoelectronics and stimulus responsive materials. This review will focus on the synthetic strategies of functional polymers with various precise moieties by ADMET over the past few decades, especially functional polyesters, polyethers, polyolefins, and conjugated polymers as well as organometallic polymers will be summarized.
Graphical Abstract
Acyclic diene metathesis not only provides facile method for the polymerization of relatively “inert” acyclic diene monomers, but also gives polymers with versatile architectures and functionalities that cannot prepared via conventional polymerization methods. This comprehensive review summarizes the rational design of monomers for ADMET polymerization and corresponding synthesis of functional polyesters, polyethers, polyolefins, and conjugated polymers as well as organometallic polymers.
... Capitalizing on the inexpensive and readily available cis-hex-4-en-1-ol and cis-oct-5-en-1-ol 30 , a variety of monomers were synthesized in one or two steps in high yields ( Fig. 2a and Supplementary Information) [31][32][33][34] . These two groups of monomers (1-4 and 5-8) were selected to interrogate the tolerance of dithiolate catalysts to polar monomers containing Lewis basic functional groups, as well as the effect of increasing the size of the capping group (Et vs Me) on the polymerization. ...
The cis/trans geometry of olefins is known to dramatically influence the thermal and mechanical properties of polyalkenamers. Yet, polymerization methods that allow the practitioner to efficiently control this parameter are scarce. Herein, we report the development of a stereoretentive acyclic diene metathesis (ADMET) polymerization that capitalizes on the unique reactivity of dithiolate Ru carbenes combined with cis monomers. These Ru catalysts exhibit exquisite retention of the cis geometry and tolerate many polar functional groups, enabling the synthesis of all-cis polyesters, polycarbonates, polyethers, and polysulfites. Additionally, the stereoretentive ADMET is characterized by low catalyst loadings and tolerance toward trans impurities in the monomer batch, which should lend to ready implementation at large-scale. Remarkably, modulation of the reaction conditions including temperature and reaction time leads to an erosion of stereoretention, thereby permitting a stereocontrolled synthesis of polyalkenamers with predictable cis:trans ratios. The impact of the cis:trans alkene content within the polymer backbone on the thermal properties was clearly demonstrated through differential scanning calorimetry and thermogravimetric analysis. Stereocontrolled ADMET provides a unique synthetic approach toward materials with precise structures and tailored properties.
... This trend is consistent with the literature on ADMET polymerization of oxygencontaining dienes using Schrock-type catalysts. 42,43 The glass transition temperatures, T g , of C 2 EO 4 (−72.8°C) and C 2 EO 5 (−67.0°C) ...
We perform a joint experimental and computational study of ion transport properties in a systematic set of linear polyethers synthesized via acyclic diene metathesis (ADMET) polymerization. We measure ionic conductivity, σ, and glass transition temperature, Tg, in mixtures of polymer and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. While Tg is known to be an important factor in the ionic conductivity of polymer electrolytes, recent work indicates that the number and proximity of lithium ion solvation sites in the polymer also play an important role, but this effect has yet to be systematically investigated. Here, adding aliphatic linkers to a poly(ethylene oxide) (PEO) backbone lowers Tg and dilutes the polar groups; both factors influence ionic conductivity. To isolate these effects, we introduce a two-step normalization scheme. In the first step, Vogel-Tammann-Fulcher (VTF) fits are used to calculate a temperature-dependent reduced conductivity, σr(T), which is defined as the conductivity of the electrolyte at a fixed value of T - Tg. In the second step, we compute a nondimensional parameter fexp, defined as the ratio of the reduced molar conductivity of the electrolyte of interest to that of a reference polymer (PEO) at a fixed salt concentration. We find that fexp depends only on oxygen mole fraction, x0, and is to a good approximation independent of temperature and salt concentration. Molecular dynamics simulations are performed on neat polymers to quantify the occurrences of motifs that are similar to those obtained in the vicinity of isolated lithium ions. We show that fexp is a linear function of the simulation-derived metric of connectivity between solvation sites. From the relationship between σr and fexp we derive a universal equation that can be used to predict the conductivity of ether-based polymer electrolytes at any salt concentration and temperature.
... As ring-strain in the monomer is not required, a wide variety of diene monomers is possible. ADMET has been used to produce polymers containing simple hydrocarbons [3,4], aromatic amines [5], branched acids [6,7], ethers [8,9], silanes [10], acetals [11], esters [12][13][14][15], aromatic moieties [16][17][18][19][20], thioethers [21], and ketones [14,22], to name a few. ...
Herein, we review the major advances in controlling polyethylene morphology through precise control of branch frequency and identity. This control is made possible by the acyclic diene metathesis reaction.
The synthesis of medium‐ and short‐chain aliphatic polyethers is industrially limited to the ring opening polymerization of cyclic ethers with a high ring strain, such as oxiranes, oxetanes or tetrahydrofuran. This structural limitation can be overcome by the gallium bromide catalyzed reduction of different polyesters into their corresponding polyethers. Herein, the scope of applicable polyesters is broadened, while the influence of the polyester structure on the reduction system is examined. The reactivity as well as side reactions, i.e., overreduction leading to chain cleavage, was shown to depend on the distance of the ester groups in the repeating unit of the polyester. Two different reducing agents, namely triethylsilane and 1,1,3,3‐tetramethyldisiloxane, are studied and compared in terms of reactivity and work‐up procedures, showing advantages and disadvantages depending on the reduced polyester properties. The reaction conditions were optimized and the reduction could be scaled‐up to 60 g polyester. All products were thoroughly characterized. This article is protected by copyright. All rights reserved
Block copolymers form the basis of the most ubiquitous materials such as thermoplastic elastomers, bridge interphases in polymer blends, and are fundamental for the development of high-performance materials. The driving force to further advance these materials is the accessibility of block copolymers, which have a wide variety in composition, functional group content, and precision of their structure. To advance and broaden the application of block copolymers will depend on the nature of combined segmented blocks, guided through the combination of polymerization techniques to reach a high versatility in block copolymer architecture and function. This review provides the most comprehensive overview of techniques to prepare linear block copolymers and is intended to serve as a guideline on how polymerization techniques can work together to result in desired block combinations. As the review will give an account of the relevant procedures and access areas, the sections will include orthogonal approaches or sequentially combined polymerization techniques, which increases the synthetic options for these materials.
Diol‐terminated polyethers are important intermediates for the manufacturing of block copolymers, but only a few polyethers other than polyethylene glycols are available on a technical scale. Most of them are highly polar. Natural fatty alcohols—converted to similar polyethers—should have a grossly reduced polarity because of a large separation of the oxygen atoms in the C18 chain. A synthesis sequence of polyethers with a longer carbon chain compared to the ethylene glycol‐derived ethers based on commercially available fatty alcohols was designed for a future examination of the hydrophobic properties. Palladium‐catalyzed cleavage of olefinic dialkyl carbonates results in carbon dioxide elimination and subsequent formation of ethers from an allyl‐palladium cation. It could be shown that this process with fatty alcohols like undec‐10‐en‐1‐ol or oleyl alcohol can be run with appreciable yield. Although carbonates were obtained here using expensive chloroformates as starting materials, transesterification of dimethylcarbonates can be used similarly. Ruthenium‐catalyzed acyclic diene metathesis (ADMET) at both chain terminations then was applied to polymerize the ethers. Depending on the alkenyl chain, short oligomers with a degree of polymerization (DP) of about 5–8 seem to be formed according to gel permeation chromatography (GPC).
Aliphatic long‐chain polyesters are a common class of renewable polymers and can be obtained by various synthetic routes, most notably from renewable fatty acids. In contrast, for aliphatic long chain polyethers only a few examples are known. Recently, the GaBr3‐catalyzed reduction of esters to ethers has been introduced as convenient post‐polymerization modification to obtain polyethers directly from polyesters. Here, this reduction is applied to synthesize fatty acid–based ω,ω′‐unsaturated diene diether monomers, which are polymerized afterward by thiol‐ene or acyclic diene metathesis (ADMET) polymerizations in the “green” solvents methyl‐THF (2‐methyltetrahydrofuran) and polarclean. After polymerization, the thiol‐ene or ADMET polymers are modified by either oxidation or hydrogenation, respectively. Aliphatic long‐chain polyethers are obtained by acyclic diene metathesis (ADMET) and thiol‐ene polymerization of fatty acid–based ω,ω′‐unsaturated ethers in the “green” solvents 2‐methyl‐THF (2‐methyltetrahydrofuran) and polarclean. To produce ω,ω′‐unsaturated ethers, the recently reported GaBr3‐catalyzed reduction of esters is utilized. The polymers are modified by either oxidation or hydrogenation, and characterized by NMR‐ and IR‐spectroscopy and DSC analysis.
The synthesis of cinchona alkaloid-derived chiral squaramide polymers using acyclic diene metathesis (ADMET) polymerization over Hoveyda-Grubbs 2nd generation catalysts (HG2) is reported herein. The C3-vinyl group in the cinchona alkaloid easily facilitates the ADMET reaction in the presence of the HG2 to form a C-C bond. The polymers were subsequently used as catalysts for the asymmetric Michael addition reaction to afford the corresponding chiral products in good yields with excellent stereoselectivities. The catalysts were easily recovered and recycled several times.
Herein, we demonstrate a novel approach for the synthesis of middle and long chain aliphatic polyethers 2 by applying the GaBr3‐catalyzed reduction with TMDS as reducing agent to polyesters 1. Thus, various linear and branched aliphatic polyesters 1 were prepared and systematically investigated for this reduction strategy, demonstrating the applicability and versatility of this new polyether synthesis protocol. Middle and long methylene chain polyethers were obtained from the respective polyesters without or with minor chain degradation, whereas short chain polyesters, such as poly‐L‐lactide 1i and poly[(R)‐3‐hydroxybutanoate] 1j, showed major chain degradation. In this way, yet unavailable and uncommon polyethers were obtained and studied.
Herein, we demonstrate a novel approach for the synthesis of middle and long chain aliphatic polyethers 2 by applying the GaBr3‐catalyzed reduction with TMDS as reducing agent to polyesters 1. Thus, various linear and branched aliphatic polyesters 1 were prepared and systematically investigated for this reduction strategy, demonstrating the applicability and versatility of this new polyether synthesis protocol. Middle and long methylene chain polyethers were obtained from the respective polyesters without or with minor chain degradation, whereas short chain polyesters, such as poly‐L‐lactide 1i and poly[(R)‐3‐hydroxybutanoate] 1j, showed major chain degradation. In this way, yet unavailable and uncommon polyethers were obtained and studied.
Placing artificial folding elements into precision polymers is an important strategy to systematically study structure formation in self-assembly, particularly in the semicrystalline state. To this purpose, a series of precision polymers bearing either a N-protected or N-unprotected diaminopyridine (DAP) unit after every 16th, 18th, and 20th carbon as well as a urea unit after every 20th carbon along a polyethylene-like polymer were synthesized via acyclic diene metathesis polymerization and subsequent hydrogenation. The polymers thus contain either H-bonds (urea/DAP), π–π-elements (DAP), or no H-bonds (respective Nprotected urea/DAP-units) in their main chain, able to consequently study the crystallization behavior under influence of such supramolecular moieties. Therefore, the thermal properties and crystallization behavior were analyzed via differential scanning calorimetry (DSC) as well as wide angle X-ray diffraction. The obtained crystalline polymer is influenced by the different supramolecular interactions existing between adjacent polymer chains and the varying defect size exerted by the incorporated functional groups. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017
Acyclic diene metathesis (ADMET) polymerization has shown to be a clean route to silicon-based unsaturated polymers. High molecular weight carbosilane and carbosiloxane polymers have been generated with Schrock's well-defined tungsten and molybdenum alkylidenes. Monomer reactivity has shown to be highly dependant on the nature of the carbon spacing between the olefin and the silicon moiety. Cyclization reactions have also been observed during bulk polymerization and in solution. In addition, chloro-functionalized silanes offer an opportunity to produce materials with a broad range of potential properties due to the reactive sites along the backbone. Further, σ, π conductive hybrid silicon polymers have been constructed which will allow the systematic study of the nondefined nature of conductivity through a σ-π system.
A review with 86 references covering chain-growth (insertion, metathesis) polymerization and step-growth (metathesis polycondensation of acyclic dienes, Heck-type polycondensation of haloarene derivatives, etc.) polymerization, promoted by catalysts based on late transition metals and each dicsussed in relation to monomer and catalyst type. The nature of catalyst's active sites is described and polymerization mechanisms are discussed. The most representative Pd-based catalysts are duly emphasized. The chain- and the step-growth models of propagation of polymerization are intercompared in terms of the oxidation state of the Pd species in the catalysts. The former mode keeps the oxidation state of palladium [Pd(II)] unaffected; the latter mode allows the oxidation state to vary from Pd(II) to Pd(0) (and back).
The multiple hydrogen-bonded unit containing polymer was synthesized by using acyclic diene metathesis polymerization of oligoamide monomer with Grubbs-type olefin metathesis catalysts. The polymer was characterized by nuclear magnetic resonance, gel permeation chromatography and scanning electron microscope. The results demonstrate the successful synthesis of novel polymer via acyclic diene metathesis polymerization and the hydrogen-bonding-assisted formation of aggregates.
The process of acyclic diene metathesis (ADMET) polymerization of an α,ω-diene begins with the metathesis of a terminal olefin and a metal methylidene complex, which produces a molecule of ethylene and a metal alkylidene via the α-substituted metallacyclobutane, where the terminal olefin can be a monomer, an oligomer, or a polymer. Many of the catalysts commonly used in ADMET polymerization are more active toward terminal olefins, because of the decreased steric hindrance compared to internal olefins. A number of hydrocarbon dienes have been utilized in ADMET polymerizations. Ethers were the first functionalized dienes to be polymerized successfully by ADMET. One of the most striking applications of ADMET in medicine has been the synthesis of polymers with pendant nonsteroidal anti-inflammatory drugs (NSAIDs). Conjugated polymers are of intense interest to the polymer community, and several groups have actively pursued the synthesis of a variety of conjugated polymers via metathesis polymerization.
Homo-telechelic polymers with two or sometimes more identical end groups are of great industrial importance, particularly for polyurethane synthesis. Mono-telechelic polymers can also be attached to a linear, multifunctional polymer to yield graft copolymers. Depending on the functional end group, such polymers can attach to macroscopic or nanoparticle surfaces or form conjugates with bio-oligomers or biomacromolecules. Controlled radical polymerizations such as atom-transfer radical polymerization (ATRP), reversible addition fragmentation chain transfer (RAFT), or nitroxide-mediated polymerizations (NMPs) can all be carried out with prefunctionalized initiators and terminated functionally, giving homo- or hetero-telechelic polymers. It is mechanistically straightforward to obtain homo-telechelic polymers via the acyclic diene metathesis (ADMET). However, this mechanism is limited to homo-telechelic polymers with a broader molecular weight distribution than can be achieved by living ring-opening metathesis polymerization (ROMP). Preparing telechelic polymers via ROMP is more challenging than via the ADMET route.
This chapter focuses on olefin metathesis transformations in green(er) organic solvents, including supercritical carbon dioxide (scCO2) and organic carbonates, in particular dimethyl carbonate (DMC) and poly(ethylene glycol) (PEG). It reviews the domain of a solvent very often quoted as the greenest or best solvent in green chemistry textbooks, namely, no solvent or solventless conditions. DCM is often used in ruthenium-catalyzed metathesis reactions as it is in general a good catalyst solvent. Recently, ring closing metathesis (RCM) of diethyl diallylmalonate (DEDAM) and cross metathesis of allylbenzene with cis-1,4-diacetoxy-2-butene were studied, both under solvent-free conditions and in methyl decanoate, a renewable and environmentally benign solvent derived from fatty acid derivatives. More recently, the synthesis of nitrogen containing heterocycles by ruthenium catalyzed RCM using low catalyst loading was studied by Grubbs.
1Introduction2Catalysts, Intermediates, Initiator Efficiencies3Acyclic Monoenes not Containing Functional Groups4Acyclic Monoenes Containing Functional Groups5The Carbonyl–Olefination Reaction6Acyclic Diene Metathesis (ADMET)7Ring-Opening Metathesis Polymerization (ROMP) Of Cycloalkenes8Copolymerization9Polymerization of Acetylenes by Olefin Metathesis Catalysts10Intramolecular Metathesis Reactions of Enynes and Dienynes11Metathesis Reactions of Alkynes Involving Total Cleavage of the CC BondKeywords:advances in metathesis of olefins;catalysts, intermediates, initiator efficiencies;second-generation catalysts (carbene catalysts);propagating metal carbene olefin complex detection;acyclic monoenes not containing functional groups;ring-closing metathesis (RCM);acetylene polymerization by olefin metathesis catalysts;enyne and dienyne intramolecular metathesis reactions
Acyclic diene metathesis (ADMET) polymerization is a powerful and versatile technique for creating precision polymers. Specialized and well-defined materials, as well as improved understanding of structure–property relationships, can be achieved by ADMET polymerization of designed symmetrical monomer structures. The introduction of functional groups into ADMET polymers, from polar groups to biodegradable moieties, has resulted in an array of precision functional materials with distinct properties and interesting applications.
Graphical abstract
The history of and major advances in the acyclic diene metathesis (ADMET) reaction are described. Because precise branch identity and frequency can be achieved by ADMET polymerizations of symmetrical α,ω-dienes, polyethylenes with precisely spaced alkyl branches of specified length have been prepared. Investigations of their morphologies and thermal properties have provided valuable insight into the behavior of polyethylene. ADMET preparation of ethylene copolymers and telechelic oligomers, as well as the properties of these materials, is also discussed.
Many hydrocarbon polymers containing heteroatom defects in the main chain have been investigated as degradable polyethylene-like materials, including aliphatic polyesters. Here, acyclic diene metathesis (ADMET) polymerization was used for the synthesis of aliphatic poly(sulfonate ester)s. The requisite sulfonate ester containing α,ω-diene monomers with varying numbers of methylene groups were synthesized, and their polymerization in the presence of ruthenium-N-heterocyclic (Ru-NHC) alkylidene catalysts was studied. A clear negative neighboring group effect (NNGE) was observed for shorter dienes, either inhibiting polymerization or resulting in low-molecular-weight oligomers. The effect was absent when undec-10-en-1-yl undec-10-ene-1-sulfonate was employed as the monomer, and its ADMET polymerization afforded polymers with appreciable number-average molecular weights of up to 37,000 g/mol and a dispersity Đ of 1.8. These polymers were hydrogenated to afford the desired polyethylene-like systems. The thermal and morphological properties of both saturated and unsaturated polymers were investigated. The incorporation of sulfonate ester groups in the polymer backbone offers an interesting alternative to other heteroatoms and helps further the understanding of the effects of these defects on the overall polymer properties.
Acyclic diene metathesis (ADMET) polymerization is a unique strategy for achieving polymers with precise control over the primary structure. This precision is obtained by specific monomer design and carefully controlled polymerization conditions. Over time, this approach has produced an array of sophisticated architectures ranging from precise polyethylenes, to hyperbranched polymers, to rotaxanes. Acyclic diene metathesis (ADMET) polymerization is a powerful tool for creating precision polymers. This review summarizes the use of ADMET polymerization to synthesize precision polyethylene model compounds and various advanced polymer structures.
Several new triptycene-containing polyetherolefins were synthesized via acyclic diene metathesis (ADMET) polymerization. The well-established mechanism, high selectivity and specificity, mild reaction conditions, and well-defined end-groups make the ADMET polymerization a good choice for studying systematic variations in polymer structure. Two types of triptycene-based monomer with varying connectivities were used in the synthesis of homopolymers, block copolymers, and random copolymers. In this way, the influence of the triptycene architecture and concentration in the polymer backbone on the thermal behavior of the polymers was studied. Inclusion of increasing amounts of triptycene were found to increase the glass transition temperature, from −44 °C in polyoctenamer to 59 °C in one of the hydrogenated triptycene homopolymers (H-PT2). Varying the amounts and orientations of triptycene was found to increase the stiffness (H-PT1), toughness (PT11-b-PO1) and ductility (PT11-ran-PO3) of the polymer at room temperature. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
Recently, we have reported the synthesis and ring-opening metathesis polymerization of enantiomerically pure and racemic methyl-N-(1-phenylethyl)-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate. In this paper, we present a new optically active 2-azanorbornene derivative that undergoes ring-opening metathesis polymerization in the presence of molybdenum alkylidene initiators of the type Mo(CH-t-Bu) (NAr)(OR2). Enantiomerically pure (1-phenylethyl)-N-(1-phenylethyl)-2-azabicyclo[2.2.1]hept-5-ene-3-carboxamide 1 can be obtained through an asymmetric Lewis-acid-catalyzed Diels–Alder reaction of cyclopentadiene with the corresponding imine of the glyoxylic amide. Ring-opening metathesis polymerization of 1 leads to the polymers, 2a and 2b, which are investigated by traditional methods such as GPC, DSC (differential scanning calorimetry) and polarimetry, as well as by ESI (electrospray ionisation)-MS (mass spectroscopy), a method that has been shown to reveal valuable information about polymer structure and end groups.
ABSTRACT
Today's olefin metathesis catalysts show high reactivity, selectivity, and functional group tolerance, and allow the design of new syntheses of precisely functionalized polymers. Here we describe a general “one-pot” synthesis for narrow polydispersity bis-end-functional (=homotelechelic) ROMP polymers exploiting the propagating ruthenium complex inherent selectivity for strained norbornenes over acyclic internal olefins. This approach represents a straightforward general method of homotelechelic polymers carrying almost any functional end group (within the limitations of the catalyst's functionality tolerance). Complete pre-functionalization of the initiator is realized in situ within minutes and without the need of further purification steps. The excess acyclic olefin re-enters the catalytic cycle after monomer consumption is complete giving a homotelechelic polymer. 1H NMR spectroscopic and MALDI-ToF-MS analysis show highly efficient end group functionalization. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013
Acyclic diene metathesis, the condensation of terminal dienes to yield high polymer, has been found to be an extremely versatile
reaction. Using the appropriate choice of catalyst, polymers containing a wide variety of functional groups have been synthesized.
A unique aspect of ADMET is its ability to produce new polymer backbones by strategic monomer design. ADMET has been utilized
to make segmented block copolymers, metal containing polymers, and regularly branched polyolefins, that are difficult to synthesize
by other means. New aspects of this chemistry are outlined, along with a discussion of the ADMET reaction mechanism, catalysts,
and kinetics.
Übergangsmetallkatalysierte C-C-Verknüpfungen gehören zu den wichtigsten Reaktionen in der organischen Synthese. Eine interessante Reaktion aus dieser Klasse ist die Olefinmetathese, ein metallkatalysierter Austausch von Alkylidengruppen zwischen Olefinen. Die Olefinmetathese ermöglicht die Spaltung und Knüpfung von C-C-Doppelbindungen. Besondere funktionelle Gruppen sind dabei nicht erforderlich. Obwohl die durch eine Vielzahl von Übergangsmetallen katalysierte Reaktion industriell genutzt wird, lag ihr Potential für die organische Synthese lange Zeit weitgehend brach. Daß dieser Dornröschenschlaf vor kurzem ein jähes Ende fand, hat mehrere Gründe. So ermöglichen neue Katalysatoren die Umsetzung hochfunktionalisierter und sterisch anspruchsvoller Olefine unter milden Reaktionsbedingungen und in hohen Ausbeuten. Ein verbessertes Verständnis der Substrat-Katalysator-Wechselwirkungen hat wesentlich dazu beigetragen, daß sich die Olefinmetathese derzeit als Synthesemethode etabliert. Außer der Herstellung von Polymeren mit maßgeschneiderten Eigenschaften eröffnet die Metathese heute auch neue Zugänge zu komplexen niedermolekularen Verbindungen. Die bereits hochentwickelte Ringschlußmetathese bewährt sich als Schlüsselschritt in der Synthese einer wachsenden Zahl von Naturstoffen. Zugleich zeichnen sich für neuentwickelte bimolekulare Metathesevarianten interessante Anwendungen ab. Fortschritte bei der selektiven gekreuzten Metathese acyclischer Olefine lassen ebenso wie vielversprechende Ansätze zur Einbeziehung von Alkinen eine weiterhin lebhafte Entwicklung der Metathesechemie erwarten.
Preparative methods of polymers containing a silicon-oxygen bond in the main-chain are systematically summarized with emphasis on recent developments in the synthesis of polycarbosiloxanes, poly(silyl ether)s, and poly(silyl ester)s.
Enantiomerically pure (1) and racemic (2) methyl-N-(1-phenylethyl)-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate were found to undergo ring opening metathesis polymerization reactions employing molybdenum alkylidene initiators of the type Mo(CH-t-Bu)(NAr)(OR)2 (Ar = 2,6-C6H3-i-Pr2; R = C(CH3)3; C(CH3)2CF3; CCH3(CF3)2) in various aprotic solvents. Chain transfer by terminal olefins such as 1-octene leads to a decrease in molecular weights which can be correlated to the amount of chain transfer agent added. In this way oligomers can be prepared with lower initiator consumption. The presence of alkylidene signals in the 1H-NMR spectra and the possibility of chain transfer by acyclic olefins strongly confirm the assumption of a molybdenum alkylidene intermediate as a propagating species in a living polymerization. From the dramatic effect the presence of even small amounts of quinuclidine added as complexing agent has on the polymerization rate of (1) employing (III), we assume, that there is hardly any complexion of the initiator by the nitrogen of the monomer, otherwise the polymerization of (1) should be very slow or even impossible. The stereochemistry of the polymers can be correlated with the electron withdrawing effect of the initiator's alkoxide ligands. Fluorinated ligands at the initiator lead to polymers with increasing cis-vinylene content. There is no significant effect of the solvent's polarity on the stereochemistry of the resulting polymers.
Acyclic diene metathesis (ADMET) polymerization of divinyltetramethyldisiloxane in the presence of rhodium [RhCl(COD)]2 and ruthenium RuCl2(PPh3)3 catalysts led predominantly to linear oligomers [M
n=1815,M
w/M
n=1.16] if the rhodium catalyst was used or to mixtures of dimeric and trimeric oligomers if the ruthenium complex was applied. The rhodium complex appeared to be the first effective catalyst for ADMET polymerization of divinyldisubstituted organosilicon compounds.
Transition metal catalyzed CC bond formations belong to the most important reactions in organic synthesis. One particularly interesting reaction is olefin metathesis, a metal-catalyzed exchange of alkylidene moieties between alkenes. Olefin metathesis can induce both cleavage and formation of CC double bonds. Special functional groups are not necessary. Although this reaction—which can be catalyzed by numerous transition metals—is used in industry, its potential in organic synthesis was not recognized for many years. The recent abrupt end to this Sleeping-Beauty slumber has several reasons. Novel catalysts can effect the conversion of highly fictionalized and sterically demanding olefins under mild reaction conditions and in high yields. Improved understanding of substrate–catalyst interaction has greatly contributed to the recent establishment of olefin metathesis as a synthetic method. In addition to the preparation of polymers with fine-tuned characteristics, the metathesis today also provides new routes to compounds of low molecular weight. The highly developed ring-closing metathesis has been proven to be key step in the synthesis of a growing number of natural products. At the same time interesting applications can be envisioned for newly developed variants of bimolecular metathesis. Improvements in the selective cross-metathesis of acyclic olefins as well as promising attempts to include alkynes as viable substrates provide for a vivid development of the metathesis chemistry.
This review article describes the recent advances of organo transition metal initiated polymerizations and copolymerizations of polar and nonpolar monomers. The article deals with Group 3–6 and Group 8–10 metal initiated polymerizations, in addition to some main group metal initiated polymerizations of ethylene. Group 3 rare earth metal complexes are by themselves very active in the absence of cocatalysts such as methylalumoxane or phenyl borates for both polar monomers such as alkyl (meth)acrylates, lactones, and cyclic carbonates, and also nonpolar monomers such as ethylene, 1-alkenes and 1,5-hexadiene. Group 4–5 complexes exhibit high catalytic activities toward the polymerizations of olefins only in the presence of methylalumoxane or phenyl borates. Group 5–6 metal carbene complexes are useful especially for polymerization of cyclic olefins and cyclic acetylenes. New catalyst systems composed of Group 8–10 metal imides and methylalumoxane or phenyl borates, show high catalytic activities for the polymerization of ethylene and olefins.
Ruthenium (e.g., RuHCl(CO)(PPh3)(3) and [RuCl2(CO)(3)](2)) and rhodium complexes (e.g., [RhX(cod)](2), where X = Cl, OSiMe3) appear to be the first effective catalysts for polycondensation of divinyl-tetramethyldisilazane (I) (ADPOL) to give poly(silazanylene-vinylene)s. Ruthenium catalysts give oligomers ((M) over bar(w) = 2380, (M) over bar(w)/(M) over bar(n) = 1.21) and a mixture of trans-tactic oligomers, respectively, while rhodium complexes lead to the formation of a mixture of cyclic and linear oligomers.
When several diallyl esters were subjected to ADMET using Grubbs "first generation" catalyst only oligomerization occurred (DPs < 7), but with allyl hex-5-enoate the product had a DP of 14, and with allyl undec-10-enoate the products usually had DPs in the range 41-79. It is suggested that with the diallyl esters an intermediate is formed in which the ester carbonyl chelates onto the metal centre and that this is sufficiently stable to suppress polymerization. One possible explanation for the successful polymerization of allyl undece-10-enoate is that it is achieved indirectly via a ring-closing metathesis (RCM) to give a macrocycle that then reacts further by an entropically driven ring-opening polymerization (ED-ROMP) to give the final polymer. A cyclo-depolymerization (CDP) involving the metathesis of substituted allyl ester moieties in a polymer backbone and ED-ROMPs involving the metathesis of substituted ally] ester moieties in macrocycles catalyzed by Grubbs' "first generation" catalyst and/or the "second generation" catalyst were also successful, (c) 2006 Elsevier B.V. All rights reserved.
Within the wealth of hydrocarbon polymers, poly(p-phenylene alkylene)s (“alkarotics”) hold a special position since they have been a long forgotten class of hydrophobic polymers. This is somewhat surprising, since the cornerstones of this polymer family cover extremely broad materials properties and the few known representatives attract attention with very favorable characteristics. In the course of this article, four new representatives of this family are presented. Whereas poly(p-phenylene octylene) (PPPO; 90°C), poly(p-phenylene hexylene) (PPPH; 120°C) and poly(p-phenylene propylene) (PPPPr; 110–130°C) have surprisingly low melting temperatures, the highly crystalline poly(p-phenylene butylene) (PPPB), melting between 200 and 225°C, meets many of the requirements that are essential for a novel, hydrophobic, processable, engineering polymer. In connection with the efforts to tailor the melting temperature of these polymers, a simple, semi-empirical methodology to estimate melting temperatures of unknown representatives of homologous series of polymers was developed and verified. By means of this approach, the melting temperatures of PPPH and PPPB could be predicted with remarkable accuracy. In addition, it was shown that the method is not restricted to the present alkarotic polymers, but it seems to have a rather broad range of applications as shown by the successful description of the polymer series, including various liquid-crystalline hydrocarbon polymers and different polyamides.
The successful acyclic diene metathesis polymerization (ADMET) of an α,ω-diene containing an acetal moiety is presented. A linear, unsaturated polyacetal is produced with a number average molecular weight of 23000 as determined by gel permeation chromatography (GPC). Thermogravimetric analysis (TGA) of the polymer reveals onsets of decomposition below 300°C in both air and nitrogen atmospheres while differential scanning calorimetry (DSC) indicates that the polymer is primarily amorphous.
Acyclic diene metathesis (ADMET) polymerization offers a viable route for the synthesis of chlorofunctionalized unsaturated carbosilane oligomers. The Si-C1 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 chlorofunctio- nalized carbosilane oligomers with known vinyl end groups. The first synthesis of an unsaturated carbosilane oligomer functionalized with a Si-CI 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.
The project goals are the synthesis of new materials having the potential for use as ion-conducting membranes. We have been able to make rugged membrane structures from a polymer of interest by first casting the polymer on a surface then exposing it to UV irradiation. These procedure generates free standing membranes that are quite durable in themselves. The initial goal has been to investigate the use of unsaturated carbosilane monomer functionalized with an Si-Cl bond in the synthesis of new materials for use as ion-conducting membranes. We've spent most of our time devising the synthesis chemistry needed to create chlorosilane monomers substituted with appropriate nucleophiles. The nucleophiles employed thus far have been diethylene glycol methyl ether and the sodium salt of 3-hydroxy-1-propane-sulfonic acid.
The term “model polymers” has long been utilized to designate linear macromolecules of controlled size and low dimensional fluctuation. Interest in these polymers was mainly motivated by the need for samples of well-controlled length, useful for the calibration of characterization techniques such as viscometry and size exclusion chromatography. Methods based on “living” polymerizations—so called because of the absence of transfer and termination reactions-proved to be the best suited for this objective. The first example of such a process was given by Szwarc [1, 2], who demonstrated that the anionic polymerization of styrene is free of the above-cited side reactions, when carried out in aprotic solvents. From the observation made while carrying on this study, Szwarc invented the concept of “living” polymerization. Since this pioneering work, many other unsaturated and heterocylic monomers have been shown to undergo “living” polymerizations through one of these five processes: anionic [3–6], cationic [7–9], metathesis [10–12], group transfer [13, 14], and even free radical [15–17]. This has led to a noticeable diversification of tailor-made linear polymers.
Reactions between alkylidene complexes of the type Mo(NR)(CHR'')(OR')2 (R = 2,6-i-Pr2C6H3, 2,6-Me2C6H3, 2-i-PrC6H4, 2-t-BuC6H4, 2-CF3C6H4, 1-adamantyl; R'' = CMe2Ph, CMe3; R' = CMe3, CMe2(CF3), CMe(CF3)2, OC(CF3)2CF2CF2CF3, C(CF3)3) and internal olefins or terminal olefins are explored. Alkylidene complexes that contain relatively electron-withdrawing alkoxide ligands are the most active for metathesis of both internal and terminal olefins. The rate of metathesis of internal olefins by monosubstituted alkylidene complexes is slowed down dramatically in DME compared to the rate in toluene. Methylene complexes are stabilized toward bimolecular decomposition in DME but still react rapidly with internal olefins. Coupling of terminal olefins to give symmetric internal olefins (largely trans) is efficient (typically 0.1 mol % catalyst) and is driven to completion by the loss of ethylene. Trans products are the result of thermodynamic control; methylene species are responsible for rapid secondary metathesis reactions. Methyl 4-pentenoate,methyl 9-decenoate, and 9-(trimethylsiloxy)-1-decene are rapidly and efficiently coupled by Mo(CHCMe2Ph)(N-2,6-i-Pr2C6H3)[OCMe(CF3)2]2 (1a). Methyl acrylate, allylcyanide, and (allyloxy)trimethylsilane were not coupled by 1a. Styrene is efficiently transformed into trans-stilbene by Mo(N-2,6-Me2C6H3)(CHMe2Ph)[OCMe2(CF3)]2 in the presence of DME, while the ''dimer'' and ''tetramer'' of divinylbenzene have been prepared by analogous methods. Asymmetric internal olefins can be prepared by using a 4-10-fold excess of one olefin.
A variety of polyethers were synthesized by a tandem approach incorporating ring-closing metathesis (RCM) followed by ring-opening metathesis polymerization (ROMP) using RuCl2(CHPh)(PCy3)2 (1) as an initiator. Unsaturated crown ether monomers, including a 12-crown-4 analogue (3), a benzocrown ether (8), and a benzocrown ether with a pendent phenylalanine methyl ester (9), were synthesized in good yields using a lithium ion as a template and 1 as a catalyst for RCM. Saponification of 9 afforded the benzocrown phenylalanine carboxylic acid monomer 10. The ROMP of 3, 8, and 9 with 1 as an initiator yielded the homopolymers 11, 12e, and 13e, respectively. The relative concentrations of 3 to 1 were varied to produce 11 with a wide range of molecular weights (Mn from 10 900 to 206 300). Hydrogenation of 11 proceeded quantitatively to yield a saturated polyether. Monomers 8 and 9 were copolymerized with 3 to generate polymers 12a−d and 13a−d, respectively. The copolymer composition corresponded to the feed ratio of the monomers. Crown ether 10 was copolymerized with 3 at a low feed ratio to form the corresponding polyether with pendent amino acids.
Molybdenum and ruthenium catalysis has been used to synthesize main-chain boronate ADMET polymers under bulk conditions; however, the long-term stability and solution characterization of these polymers are dramatically influenced by ligand-exchange reactions within the boronate moiety. Placing the boronate pendent to the main chain obviates this phenomenon as demonstrated in the ROMP polymerization of norbornene monomers with boronates both in exo and endo positions. The stereochemistry of the monomer influences both the rate of polymerization and the microstructure of the resulting polymer; these effects are more pronounced in the case of ruthenium catalysis. The thermal stability of these polymers also is dependent upon monomer stereochemistry.
The synthesis of the first high molecular weight polymers by acyclic diene metathesis (AD-MET) polymerization is reported, using a catalyst free of Lewis acids. Previous attempts, most recently in our laboratory and in several other laboratories over the past 20 years, had proven to be unsuccessful. 1,9-Decadiene has been converted to poly(octenylene), and 1,5-hexadiene has been converted to exclusively 1,4-polybutadiene by this procedure. The metathesis polymerization reaction is quantitative at or near room temperature and yields only polymer and ethylene as a byproduct. No other products are observed. Poly-(octenylene) exhibits a minimum weight-average molecular weight of 108 000 and is more than 90% trans in its stereochemistry. Exclusively 1,4-polybutadiene is of a minimum weight-average molecular weight of 28 000 and is more than 70% trans in its stereochemistry. The stereochemistry appears to be controlled thermodynamically due to the equilibrium nature of the polymerization, and this stereochemical feature distinguishes ADMET polymerization from ring-opening metathesis polymerization (ROMP).
Allylic type ethers R′CHCHCH2OR do not undergo metathesis reaction but react with the catalysts to give stable [C12W(OR)3]2. The unsaturated moiety of the ethers reacts with the solvents, PhCl, to give the corresponding allylic derivatives.RésuméLes éthers allyliques du types R′CHCHCH2OR ne subissent pas la réaction de métathèse mais réagissent avec les catalyseurs de métathèse pour donner des composés [Cl2W(OR)3]2 stables. La partie insaturée de l'éther réagit avec le solvant, le chlorobenzène, pour donner les dérivés allyliques correspondants.
Metathesis of olefinic amines has been studied with two purposes: (i) to try to carry out at a stoichiometric (or slightly catalytic) level metathesis of olefinic amines to obtain telechelic compounds; (ii) to try to find which parameters play a role in the catalytic process.Two types of catalytic systems were found to be moderately active in the metathesis of olefinic amines: W(CO)5L or W(CO)3(Arene) (Arene = benzene, toluene, mesitylene) associated with a large excess of C2H5AlCl2 and O2.M(NO)2X2L2 associated with an excess of C2H5AlCl2 (X = Cl, Br; M = Mo, W).The substituents on the nitrogen were found to determine the resulting reactivity of the olefinic amine: steric as well as electronic effects play a role on the acid-base equilibrium between the amine and the Lewis acid cocatalyst. The distance between the double bond and the amine group shows a sharp maximum for olefins of the type CH2CH(CH2)3N(R)(R′). The results are tentatively explained on the basis of an intramolecular stabilization of the metallocarbene moiety by the amine group; this would increase the lifetime of the catalyst. Stereochemical studies seem to indicate that there is no modification of stereochemistry between functionalized and non-functionalized olefins. Consequently the intramolecular stabilization of the metallocarbene moiety and the amine group does not occur in the metallo-cyclobutane transition state formation.
Various alkenes carrying functional groups are metathesized, with a high selectivity, with the catalyst system Re2O7–Al2O3, promoted by a small amount of tetramethyltin.
W(CH-t-Bu)(NAr)[OCMe2(CF3)]2 (Ar = 2,6-C6H3-i-Pr2) reacts with methyl acrylate to give the metallacyclobutane complex W[CH(t-Bu)CH2CH(CO2Me)](NAr)[OCMe2(CF 3)]2 (1). 1 belongs to the space group P21/c with a = 17.323 (3) Å, b = 10.408 (3) Å, c = 18.758 (3) Å, V = 3337 (2) Å3, Mr = 769.52, ρ(calcd) = 1.531 g cm-3, Z = 4, and μ = 37.33 cm-1 (R = 0.043, Rw = 0.043). The complex has an approximately square-pyramidal core geometry with the carbonyl oxygen atom bound weakly trans to the apical imido ligand. The four basal sites are occupied by the two alkoxide oxygen atoms and the two α-carbon atoms of the metallacyclobutane ligand. Similar reactions may be carried out between M(CH-t-Bu) (NAr)-[OCMe2(CF3)]2 or M(CH-t-Bu)(NAr)(O-t-Bu)2 and N,N-dimethylacrylamide to give metallacyclobutane complexes of the type M[CH(t-Bu)CH2CH(CONMe2)](NAr)(OR)2 (OR = OCMe2(CF3), O-t-Bu; M = W, Mo). 1 reacts with trimethylphosphine to give W(CH-t-Bu)(NAr)[OCMe2(CF3)]2(PMe3), but complexes of the type W[CH(t-Bu)CH2CH(CONMe2)](NAr)(OR)2 (OR = OCMe2(CF3), O-t-Bu) do not react readily with trimethylphosphine. Differences in reactivity of the methyl acrylate and the dimethylacrylamide tungsten complexes with ethylene are analogous. In contrast, Mo[CH(t-Bu)CH2CH(CONMe2)](NAr)(O-t-Bu)2 is in equilibrium with Mo(CH-t-Bu)(NAr)(O-t-Bu)2 and free N,N-dimethylacrylamide in solution.
The reaction between Mo(C-t-Bu)(dme)Clâ (dme = 1,2-dimethoxyethane) and MeâSiNHAr (Ar = 2,6-diisopropylphenyl) yields Mo(C-t-Bu)(NHAr)Clâ(dme) (1), which upon treatment with a catalytic amount of NEtâ is transformed into Mo(CH-t-Bu)(NAr)Clâ(dme) (2). Complexes of the type Mo(CH-t-Bu)(NAr)(OR)â (OR = OCMe(CFâ)â, OCMeâ(CFâ), O-t-Bu, or OAr) have been prepared from 2. Complexes of the type Mo(C-t-Bu)(NHAr)(OR)â (OR = OCMe(CFâ)â or OAr) have been prepared from 1, but they cannot be transformed into Mo(CH-t-Bu)(NAr)(OR)â complexes. A precursor to imido alkylidene complexes that is related to 2 has been prepared by the sequence MoOâ â MoOâClâ â Mo(NAr)âClâ â Mo(NAr)â(CHâRâ²)â â Mo(CHRâ²)(NAr)(OTf)â(dme) (Râ² = t-Bu or CMeâPh; OTf = OSOâCFâ). Mo(CH-t-Bu)(NAr)(OTf)â(dme) crystallizes in the space group P{anti 1} with a = 17.543 â«, b = 19.008 â«, c = 9.711 â«, α = 91.91°, β = 99.30°, γ = 87.27°, Z = 4, M{sub r} = 729.60, V = 3,191.1 â«Â³, Ï(calcd) = 1.518 g cmâ»Â³.
The reaction of a series of diallylamines and related compounds with free radicals in aqueous acid solution has been studied in a flow system using ESR spectroscopy. The initiation was by radicals generated from titanium trichloride-hydrogen peroxide (hydroxyl radicals) and titanium trichloride-hydroxylamine (amino radicals) systems, respectively. The observed ESR spectra were assigned to five-membered ring radicals as the major radical species present in the system. However, the dimethallyl-amine series gave both five - and six-membered ring radicals.
By use of 1 as a ring-opening olefin metathesis catalyst, norbornene was polymerized and the resulting living polymer allowed to react with benzophenone to give diphenylethylene-capped polymer 3. The percentage of polymer chains end capped was 70-100% as determined independently by 1H NMR and UV absorbance. Additionally, there was minimal change in the molecular weights and polydispersities of the polymers during the end-capping reaction.
A series of symmetrical alpha,omega-unsaturated thioethers have been polymerized under standard acyclic diene metathesis (ADMET) conditions. Poly(thio-3-hexene-1,6-diyl)(7), poly(thio-4-octene-1,8-diyl) (8), and poly(thio-5-decene-1,10-diyl)(9) were synthesized in bulk from the corresponding bis(alkenyl) sulfides (2, 3, and 4, respectively) in the presence of the catalyst Mo(CHCMe2Ph)(N-2,6-C6H3-i-Pr2)(OCMe(CF3)2)2 (5). Poly[(thio-5-decene-1,10-diyl)-co-(1-octenylene)] (10) was prepared from the copolymerization of bis-(5-hexenyl) sulfide (4) and 1,9-decadiene. The polymerizability of the alpha,omega-dienes appears to be a function of the number of methylene spacers between the sulfur moiety and the terminal olefin. In the case of the monomer diallyl sulfide (1), where one methylene spacer is present, no polymerization was observed in the bulk, but rapid cyclization to 2,5-dihydrothiophene (6) was observed in solution. All polymers were characterized by H-1 NMR, C-13 NMR, and IR spectroscopies as well as elemental analysis, GPC, TGA, and DSC. These results suggest that sulfur-containing polymers are now accessible via ADMET polymerization.
Telechelic polybutadiene oligomers Si(Me) 2 (R)CH 2 (CH=CHCH 2 CH 2 ) n CH=CHCH 2 Si(Me) 2 R (R= Me, n= 2,3,4 and R= Cl, n=1) were prepared by the metathesis depolymerization of polybutadienes using allylsilane monoenes and Lewis acid-free alkylidenes.
The first acyclic diene metathesis (ADMET) polymerization of carbonate containing monomers using the molybdenum catalyst, Mo(CHCMe2Ph)(N-2,6-C6H3-i-Pr2)[OCCH3(CF3)2]2 is reported. Bis(1-hexenyl) carbonate, bis(1-pentenyl) carbonate, bis(1-butenyl) carbonate; and 4,4'-isopropylidenebis(phenyl 1-butenylcarbonate) successfully undergo ADMET homopolymerization. These polymerizations are initiated under bulk conditions and are continued in solution to produce poly(5-decenyl carbonate), poly(4-octenyl carbonate), poly(3-hexenyl carbonate), and poly(oxycarbonyloxy-1,4-phenyleneisopropylidene-1,4-phenyleneoxycarbonyl-1,6-hex-3-enylene), respectively. No metathesis activity is observed for bis(1-propenyl) carbonate due to a negative neighboring group effect. This effect involves either the coordination of the carbonyl oxygen to the metal center or simply the polarization of the double bond such that the intermediates of the metathesis process are not favored. All polymer structures were characterized by IR, H-1 NMR, and C-13 NMR spectroscopy. Number-average molecular weights were determined by end-group analysis and vapor pressure osmometry. Synthesis, characterization, and the general limitations of this polymerization are discussed.
The first equilibrium polycondensation polymerization approach to unsaturated poly(carbo- (dimethy1)silanesl is presented. Diallyldimethylsilane (I), 4,4,7,7-tetramethyl-4,7-disiladeca-1,9-diene (11), and 1,4-bis(allyldimethylsilyl)benzene (111) undergo acyclic diene (metathesis (ADMET) polymerization when catalyzed by highly active tungsten alkylidenes, ( (CF~)ZCH~CO)Z(N-~,~-C~H~-~-P~Z) W=CHC(CH&R, where R = CH3 or Ph. These polymerizations, which are performed under bulk conditions, continuously release ethylene to give poly(l,l-dimethyl-l-silapent-3-ene) (VI), poly( 1,1,4,4-tetramethyl-1,4-disilaoct-6-ene) (VII), and poly( l-(dimethylsilyl)-4-(l,l-dimethylsilapent-3-en-l-yl)phenylene) (VIII), respectively. Polymers VI
The reaction between W(C-t-Bu)(dme)Cl3 and ArNH(TMS) (Ar = 2,6-C6H3-i-Pr2) yields W(C-t-Bu)(NHAr)(dme)Cl2. In the presence of a catalytic amount of triethylamine, W(C-t-Bu)(NHAr)(dme)Cl2 is transformed into W(CH-t-Bu)(NAr)(dme)Cl2 quantitatively. Derivatives of the type W(CH-t-Bu)(NAr)(OR)2 [OR = O-t-Bu, OCMe2(CF3), OCMe(CF3)2, and OC(CF3)2(CF2CF2CF3)] have been prepared. The X-ray structure of W(CHPh)(NAr)[OCMe(CF3)2]2 (prepared by treating W(CHEt)(NAr)[OCMe(CF3)2]2 with cis-β-methylstyrene) showed it to be pseudotetrahedral with a W=C bond of 1.859 (22) Å and an alkylidene ligand turned so Hα and the phenyl ring lie in the Cα-W-N plane with the phenyl ring pointing toward the imido nitrogen atom. (Structure parameters: a = 11.57 (3) Å, b = 12.719 (2) Å, c = 21.192 (9) Å, V = 3118.9 Å3, space group = P212121, Z = 4, with R1 = 0.089, and R2 = 0.096.) Addition of Me3SiCH=CH2 to W(CH-t-Bu)(NAr)[OCMe(CF3)]2 yielded the tungstacyclobutane complex W[CH(SiMe3)CH(SiMe3)CH2](NAr)[OCMe(CF 3)2]2 whose crystal structure showed it to be a pseudo trigonal bipyramid with an axial imido ligand and an equatorial, bent (29.9°), tungstacyclobutane ring with W-C bond lengths of 2.099 (11) and 2.066 (11) Å. (Structure parameters: a = 18.049 (4) Å, b = 12.224 (4) Å, c = 18.877 (5) Å, β = 114.86 (2)°, V = 3778.9 Å3, space group P21/n, Z = 4, with R1 = 0.054, and R2 = 0.058.) Vinyltrimethylsilane is not metathesized; W[CH(SiMe3)CH(SiMe3)CH2](NAr)[OCMe(CF 3)2]2 loses only vinyltrimethylsilane in solution to give W(CHSiMe3)(NAr)[OCMe(CF3)2]2. W(CH-t-Bu)[(NAr)[OCMe(CF3)2]2 reacts rapidly with cis-3-hexene to give a mixture of W(CHEt)(NAr)[OCMe(CF3)2]2 and W[CHEtCHEtCHEt](NAr)[OCMe(CF3)2]2; the latter loses 3-hexene completely in solution at 25°C to give the former. W(CH-t-Bu)(NAr)[OCMe2(CF3)]2 reacts much more slowly with an equilibrium mixture of trans- and cis-3-hexene to give W(CHEt)(NAr)[OCMe2(CF3)]2 in a reaction that is first order in tungsten and first order in 3-hexene. W(CH-t-Bu)(NAr)(O-t-Bu)2 reacts very slowly with vinyltrimethylsilane and virtually not at all with cis-3-hexene, while W(CH-t-Bu)(NAr)[OC(CF3)2(CF2CF 2CF3)]2 reacts slowly with each to give unstable products. W(CH-t-Bu)(NAr)[OC(CF3)2(CF2CF 2CF3)]2 will react rapidly with ethylene, however, to give an unsubstituted tungstacyclobutane complex whose structure is analogous to that of W[CH(SiMe3)CH(SiMe3)CH2](NAr)[OCMe(CF 3)2]2, except that the WC3 ring is absolutely planar. (Structure parameters: a = 18.355 (10) Å, b = 9.513 (11) Å, c = 19.976 (26) Å, β = 96.75 (8)°, V = 3463.9 Å3, space group P21/n, Z = 4, with R1 = 0.076, and R2 = 0.092.) An analogous W(CH2CH2CH2)(NAr)[OCMe(CF3) 2]2 complex can be prepared. W(CH-t-Bu)(NAr)(OR)2 complexes (where OR = O-t-Bu or OCMe2(CF3)) react with ethylene, but the ultimate products could not be characterized readily. Reactions involving 1-pentene in all cases are relatively complex. cis-2-Pentene is metathesized rapidly by OCMe(CF3)2 and OCMe2(CF3) complexes. Unsubstituted tungstacycles react with PMe3 to yield methylene complexes of the type W(CH2)(NAr)(OR)2(PMe3) [OR = OCMe(CF3)2 or OC(CF3)2(CF2CF2CF3)].
: Anti rotamers of Mo(CHCMe2Ph)(NAr)(OR)2 complexes (Ar = 2,6-C6H3-i- Pr2; OR = OCMe2(CF3), OCMe(CF3)2, and OC(CF3)2(CF2CF2CF3)) can be generated at -80 deg in toluene by photolysis at 366 nm and the rate of conversion of anti to syn rotamers determined by NMR methods. At equilibrium the anti rotamers can be observed by high field proton NMR at 25 deg after many transients and values for Keq(syn/anti) thereby determined. Keq can be determined at O deg when OR = OCMe3 and k anti/syn estimated. The rate of conversion of the anti to the syn rotamer in toluene is found to vary by at least five orders of magnitude as the alkoxide is changed from t-butoxide to OC(CF3)2(CF2CF2CF3). The results in THF are analogous, although the rates of rotamer interconversion are much slower for any given alkoxide. Addition of 2,3-bis(trifluoromethyl)norbornadiene to mixtures containing both anti and syn Mo(CHCMe2Ph)(NAr)OCMe(CF3)2)2 showed that in both toluene and THF the anti rotamer was orders of magnitude more reactive than the syn rotamer.
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Trimethylphosphine, PMe3, is shown to bind reversibly to the alkylidene complex W(CH-t-Bu)(NAr)(O-t-Bu)2 (1, Ar = 2,6-diisopropylphenyl), and the binding constants at several temperatures are measured (DELTA-H-degrees = -15.7 kcal/mol, DELTA-S-degrees = -40.7 eu). In the presence of PMe3, 1 catalyzes the living ring-opening metathesis polymerization (ROMP) of cyclobutene to yield polybutadiene with a polydispersity index (PDI) as low as 1.03, based on gel permeation chromatography versus polystyrene standards. The polymerization in the presence of PMe3 is first order in monomer and catalyst concentrations with DELTA-DELTA-G 273K = 19.8 kcal/mol, DELTA-DELTA-H(p) = 20.8 kcal/mol, and DELTA-DELTA-S(p) = 4 eu. The observed rate of initiation of the polymerization is much greater than the rate of propagation. In the absence of trimethylphosphine, the polydispersity of the polymer produced with 1 is broader (PDI > 2) due to the rate of propagation being much greater than that of initiation and the existence of chain termination. This difference is attributed to the fact that PMe3 binds more strongly to the propagating alkylidene complex than to the more sterically bulky initiating neopentylidene.
The Ring Opening Metathesis Polymerization (ROMP) of a series of cyclic alkenes bearing heteroatom functionality has been performed using a classical WCl6-based catalyst system. All of the alkenes studied exhibited significantly slower polymerization rates compared with the hydrocarbon monomer dicyclopentadiene (DCPD), this being most pronounced for monomers containing a tertiary nitrogen atom substituted at the 2 position of the norbornene skeleton. Cyclic alkene anhydrides, prepared by the Diels-Alder addition of cyclopentadiene to maleic and itaconic anhdrides, were found to be polymerizable with high yields giving cross-linked polymers which exhibited very high glass transition temperatures. Monofunctional cyclic imide derivatives of the cyclopentadiene-itaconic anhydride adduct were found to be polymerizable to moderate molecular weight thermoplastic materials with high glass transition temperatures, whilst difunctional cyclic imide derivatives led to cross-linked thermoset polymers. The solution copolymerizations of the cyclopentadiene-maleic anhydride adduct with DCPD, and of a cyclic imide derivative of the cyclopentadiene-itaconic anhydride adduct with DCPD, were carried out to form copolymers in high yields having glass transition temperatures intermediate between those of the respective homopolymers.
The first acyclic diene metathesis (ADMET) polymerization of unsaturated ketone containing monomers using the molybdenum catalyst, Mo(CHCMe2Ph)(N-2,6-C6H3-i-Pr2)[OCCH3(CF3)2]2 is reported. 6,6,8,8-Tetramethyl-1,12-tridecadiene-7-one undergoes homopolymerization; copoly-merizations are carried out with 1,9-decadiene and 2,12-dimethyl-2,12-dipentenylcyclododecan-1-one, 2,12-diallylcyclododecan-1-one, and trans-2,12-diallyl-2,12-dimethylcyclododecan-1-one These polymerizations are initiated under bulk conditions and are continued in solution. No evidence of Wittig chemistry is observed between the carbonyl functional group and the catalyst when a high degree of steric hindrance exists around the carbonyl moiety. Polymer structures were characterized by IR, 1H NMR, and 13C NMR spectroscopy. Molecular weights were determined by endgroup analysis and gel permeation chromatography.
The facile reversibility of acyclic diene metathesis (ADMET) polymerization is reported; by driving this equilibrium, condensation type polymerization toward monomer with an excess of ethylene, polymers synthesized by ADMET (poly(1-octenylene) polynorbornene) and three commercial elastomers (polybutadiene, polyisoprene and a Kraton sample) can be depolymerized according to the reaction (=CH−R−CH=) n +CH 2 =CH 2 ⇇CH 2 =CH−R−CH=CH 2
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