Poly(ɛ-caprolactone-co-ω-pentadecalactone) electrospun fibers

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Orthopalladated triarylphosphite complexes as highly efficient catalysts in the Heck reaction

An orthopalladated complex of commercially available tris(2,4-di-tert-butylphenyl)phosphite proves to be an extremely active catalyst in the Heck arylation of alkenes, with turnover numbers of up to 5,750,000 (mol product.mol Pd⁻¹) and turnover frequencies of up to nearly 300,000 (mol product.mol Pd⁻¹.h⁻¹).     

Use of samarium (III) acetate as initiator in ring-opening polymerization of trimethylene carbonate

Abstract

In this work was evaluated the activity of samarium acetate (III) (Sm(OAc)₃) as a possible initiator in the polymerization by ring opening of trimethylene carbonate (TMC). All polymerizations were carried out under solvent-free melt conditions in ampoules-like flasks, equipped with a magnetic stirrer. The effects of different parameters of reaction, such as molar ratio monomer to initiator, temperature and reaction time, on typical variables of polymers, e.g., conversion of TMC to poly(trimethylene carbonate) (PTMC), dispersity and molar mass, were analyzed. The molar ratio of monomer to initiator was varied between 0 and 1000?mol/mol and the temperature among 70 and 150?°C. Nuclear Magnetic Resonance (¹H-NMR and HMBC) and Size Exclusion Chromatography (SEC) were used to characterize the polymers. The results indicate that the Sm(OAc)₃ induces the polymerization of TMC to high conversion with number-average molecular weights of 3.11?×?10³ to 38.40?×?10³?Da. Based on the ¹H-NMR end-group analysis of low-molecular-weight PTMC, it was proposed a coordination–insertion mechanism for the polymerization, with a breakdown of the acyl-oxygen bond of the TMC. In according to the kinetic study carried out, the polymerization rate is first-order with respect to monomer concentration with apparent rate constants of k_ap?=?7.02?×?10^?4?mol?×?L^?1?×?h^?1.     

DFT study of the role of substituents in tin(II) bis(amidoethyl)amine complexes used for ε-caprolactone polymerization

DFT simulations of ring-opening polymerization of ε-caprolactone in the presence of two stannylenes based on bis(2-amidoethyl)amine ligands demonstrated that rate limiting step of the whole process is the nucleophilic attack of a metal initiator with the formation of the tetrahedral carbon from sp² carbon atom of the carboxy group. The presence of electron-withdrawing groups at the terminal nitrogen atoms of the ligands leads to decrease in the activation energy of the rate limiting step.     

Polymers of carbonic acid. XIV. High molecular weight poly(trimethylene carbonate) by ring-opening polymerization with butyltin chlorides as initiators

Numerous BuSnCl, Bu₂SnCl, and Bu₃SnCl-initiated polymerizations of cyclo(tri-methylene carbonate) (TMC) were conducted in bulk. In addition to the initiator, reaction time, temperature, and monomer/initiator (M/I) ratio were varied. Yields above 90% were obtained with all three initiators, but their reactivities decrease in the order BuSnCl₃ > Bu₂SnCl₂ > Bu₃SnCl. The maximum molecular weights decrease in the same order. With BuSnCl₃ M_ws up to 250,000 were obtained. These molecular weights were determined by GPC on the basis of the universal calibration method. In this connection Mark-Houwink equations for two solvents, tetrahydrofuran (THF) and CH₂Cl₂ were determined and compared with literature data. Furthermore, mechanistic aspects were studied. ¹H- and ¹³C- NMR spectra revealed that BuSnCl₃ forms complexes with the CO-group of TMC, whereas Bu₂SnCl₃ do not cause NMR spectroscopic effects. Kinetic studies in chloroform and nitrobenzene and a comparison with Bu₃SnOMe suggest that at least BuSnCl₃ initiates a cationic mechanism. However, in contrast to SnCl₄ (or SnBr₄), BuSnCl₃ does not cause decarboxylation. Regardless of the initiator ¹H-NMR spectroscopy revealed CH₂OH and CH₂CI endgroups in all cases. © 1995 John Wiley & Sons, Inc.     

Controlled ring‐opening polymerization of trimethylene carbonate and access to PTMC‐PLA block copolymers mediated by well‐defined N‐heterocyclic carbene zinc alkoxides

Four novel Zinc–NHC alkyl/alkoxide/chloride complexes ( 4 , 5 , 9 and 9′ ) were readily prepared and fully characterized, including X‐ray diffraction crystallography for 5 and 9′ . The reaction of N‐methyl‐N′‐butyl imidazolium chloride ( 3.HCl ) with ZnEt₂ (2 equiv.) afforded the corresponding [(C_NHC)ZnCl(Et)] complex ( 4 ) via a protonolysis reaction, as deduced from NMR data. The alcoholysis of 4 with BnOH led to quantitative formation of the dinuclear Zn(II) alkoxide species [(C_NHC)ZnCl(OBn)]₂ ( 5 ), as confirmed by X‐ray diffraction analysis. The NMR data are in agreement with species 5 retaining its dimeric structure in solution at room temperature. The protonolysis reaction of N‐(2,6‐diisopropylphenyl)‐N′‐ethyl methyl ether imidazolium chloride ( 8.HCl ) with ZnEt₂ (2 equiv.) yielded the [(C_NHC)ZnCl(Et)] species 9 . The latter was found to be reactive with CH₂Cl₂ in solution and to cleanly convert to the corresponding Zn(II) dichloride [(C_NHC)ZnCl₂]₂ ( 9′ ), whose molecular structure was also elucidated using X‐ray diffractometry. Unlike Zn(II)–NHC alkoxide species 1 and 2 , which contain a NHC flanked with an additional N‐functional group (i.e. thioether and ether, respectively), the Zn(II) alkoxide species 5 incorporates a monodentate NHC ligand. The Zn(II) complexes 1 , 2 and 5 were tested in the ring‐opening polymerization (ROP) of trimethylene carbonate (TMC). All three species are effective initiators for the controlled ROP of trimethylene carbonate, resulting in the production of narrow disperse PTMC material. Initiator 1 (incorporating a thioether moiety) was found to perform best in the ROP of TMC. Notably, the latter also readily undergoes the sequential ROP of TMC and rac‐LA in the presence of a chain‐transfer agent, leading to well‐defined and high‐molecular‐weight PTMC/PLA block copolymers. Copyright © 2014 John Wiley & Sons, Ltd.     

Polymerization mechanism of trimethylene carbonate carried out with zinc(II) acetylacetonate monohydrate

The proposed mechanism of initiation and course of ring‐opening polymerization of cyclic trimethylene carbonate (TMC) involving zinc(II) acetylacetonate is in accordance with the mechanism of monomer activation. At the first stage of the process, coordination of carbonate to Zn(Acac)₂ · H₂O complex occurs with the release of weakly coordinated water molecules. This free water molecule reacts with active TMC–Zn(Acac)₂ complex. The reaction results in the formation of propanediol and CO₂ emission. During further stages of the investigated process, the formed propanediols, or later the oligomeric diols produced with polymerization, are cocatalysts of the chain propagation reaction. The chain propagation occurs because of repeating activation of the TMC monomer through the creation of an active structure resulting in the exchange/transfer reaction between the zinc complex and the monomer, with its following attachment to the hydroxyl groups, carbonate ring opening, and formation of the carbonic unit of polymer chain. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Phosphoraneiminato tungsten alkylidyne complexes as highly efficient alkyne metathesis catalysts

The tungsten neopentylidyne complexes [Me₃CCW(NPR₃){OCMe(CF₃)₂}₂] (3a, R = Cy; 3b, R = iPr) were prepared in excellent yields by the reaction of the solvate complex [Me₃CCW{OCMe(CF₃)₂}₃(DME)] (DME = 1,2-dimethoxyethane) with equimolar amounts of the corresponding phosphoraneiminato lithium species R₃PNLi (R = Cy, iPr) at room temperature. The products were characterized by ¹H, ¹³C{¹H}, ¹⁹F{¹H} and ³¹P{¹H} NMR spectroscopy and elemental analysis. Single crystals of both complexes were obtained from diethyl ether solutions at −35 °C, and the molecular structures were determined by X-ray diffraction analysis. Complexes 3a and 3b are able to efficiently catalyse alkyne cross-metathesis (ACM) of 3-pentynyl benzyl ether (4) and ring-closing alkyne metathesis (RCAM) of bis(3-pentynyl)adipate (6) at room temperature and with low catalyst loadings (1 or 2 mol%) to afford the diether 5 and the cyclic diester 7 in virtually quantitative yields. The reactions were carried out in the presence of molecular sieve 5 Å to adsorb 2-butyne during the metathesis.     

Tailored molybdenum imido alkylidene N-heterocyclic carbene complexes as latent catalysts for the polymerization of dicyclopentadiene

Three novel molybdenum imido alkylidene N-heterocyclic carbene (NHC) pre-catalysts, that is, Mo(N-t-Bu)(1-(2,6-diisopropylphenyl)-3-isopropyl-4-phenyl-1H-1,2,3-triazol-5-ylidene)(CHCMe₂Ph)(OTf)₂ ( I1 , OTf = CF₃SO₃), Mo(N-t-Bu)(1-(2,6-diisopropylphenyl)-3-isopropyl-4-phenyl-1H-1,2,3-triazol-5-ylidene)(CHCMe₂Ph)(OTf)(t-BuO) ( I2 ) and Mo(N-2,6-Me₂-C₆H₃)(1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene)(CHCMe₂Ph)(OTf)₂ ( I3 ) are presented. Compared to complexes based on imidazol-2-ylidenes or imidazolin-2-ylidenes, (1-(2,6-diisopropylphenyl)-3-isopropyl-4-phenyl-1H-1,2,3-triazol-5-ylidene) used in precatalysts I1 and I2 exerts a comparably strong trans effect to the triflate groups trans to the NHC, while (1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene) used in I3 has a weaker trans effect on the triflate. In combination with a suitable second anionic ligand at molybdenum, that is, OTf, t-BuO, compounds I1 – I3 require higher temperatures to become active and can thus be used as truly room temperature latent pre-catalysts, even for a highly reactive monomer such as dicyclopentadiene (DCPD). When used as latent precatalysts, I1 – I3 offer access to poly-DCPD with different degrees of cross-linking and glass-transition temperatures (T_g). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3028–3033     

Magnesium complexes incorporated by sulfonate phenoxide ligands as efficient catalysts for ring‐opening polymerization of ε‐caprolactone and trimethylene carbonate

Two novel sulfonate phenol ligands—3,3′‐di‐tert‐butyl‐2′‐hydroxy‐5,5′,6,6′‐tetramethyl‐biphenyl‐2‐yl 4‐X‐benzenesulfonate (X?CF₃, L^CF3 ‐H, and X?OCH₃, L^OMe ‐H)—were prepared through the sulfonylation of 3,3′‐di‐tert‐butyl‐5,5′,6,6′‐tetramethylbiphenyl‐2,2′‐diol with the corresponding 4‐substituted benzenesulfonyl chloride (1 equiv.) in the presence of excess triethylamine. Magnesium (Mg) complexes supported by sulfonate phenoxide ligands were synthesized and characterized structurally. The reaction of MgⁿBu₂ with L‐H (2 equiv.) produces the four‐coordinated monomeric complexes ( L^CF3 )₂Mg ( 1 ) and ( L^OMe )₂Mg ( 2 ). Complexes 1 and 2 are efficient catalysts for the ring‐opening polymerization of ε‐caprolactone (ε‐CL) and trimethylene carbonate (TMC) in the presence of 9‐anthracenemethanol; complex 1 catalyzes the polymerization of ε‐CL and TMC in a controlled manner, yielding polymers with the expected molecular weights and narrow polydispersity indices (PDIs). In ε‐CL polymerization, the activity of complex 1 is greater than that of complex 2 , likely because of the greater Lewis acidity of Mg²⁺ metal caused by the electron‐withdrawing substitute trifluoromethyl (? CF₃) at the 4‐position of the benzenesulfonate group. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3564–3572, 2010     

2-Benzoimidazol-8-alkylquinolinylnickel(II) complexes as efficient catalysts for ethylene oligomerization and vinyl polymerization of norbornene

A series of nickel complexes LNiCl₂ (C1–C16), where L represents 2-benzoimidazol-8-alkylquinoline and its derivatives, were prepared as potential catalysts for the oligomerization of ethylene. The molecular structure of a representative complex C2·CH₃CH₂OH was determined by single-crystal X-ray diffraction. Upon treatment with diethylaluminium chloride (Et₂AlCl), all nickel complex pre-catalysts exhibited good activities in the oligomerization of ethylene. Furthermore, in the presence of methylaluminoxane (MAO), the nickel pre-catalysts were suitable for vinyl polymerization of norbornene.     

叔胺类环钯化合物在催化Heck反应的应用

首次报道了叔胺类环钯化合物1～4在催化Heck反应中的应用。实验表明该类化合物能高效地催化Heck反应;其中催化剂4的TON值(产品摩尔数与钯摩尔数的比值)和TOF值(产品摩尔数与钯摩尔数以及反应时间的比值)分别高达9.6×10^6和8.7×10^5)。这上迄今为止催化Heck反应的最好结果。     

Di‐nuclear zinc complexes containing tridentate imino‐benzotriazole phenolate derivatives as efficient catalysts for ring‐opening polymerization of cyclic esters and copolymerization of phthalic anhydride with cyclohexene oxide

Zinc catalysts incorporated by imino‐benzotriazole phenolate ( IBTP ) ligands were synthesized and characterized by single‐crystal X‐ray structure determinations. The reaction of the ligand precursor ( ^C1DMeIBTP ‐H or ^C1DIPIBTP ‐H) with diethyl zinc (ZnEt₂) in a stoichiometric proportion in toluene furnished the di‐nuclear ethyl zinc complexes [(μ‐ ^C1DMeIBTP )ZnEt]₂ ( 1 ) and [(μ‐ ^C1DIPIBTP )ZnEt]₂ ( 2 ). The tetra‐coordinated monomeric zinc complex [( ^C1PhIBTP )₂Zn] ( 3 ) or [( ^C1BnIBTP )₂Zn] ( 4 ) resulted from treatment of ^C1PhIBTP ‐H or ^C1BnIBTP ‐H as the pro‐ligand under the similar synthetic method with ligand to metal precursor ratio of 2:1. Single‐crystal X‐ray diffraction of bimetallic complexes 1 and 2 indicates that the ^C1DMeIBTP or ^C1DIPIBTP fragment behaves a NON‐tridentate ligand to coordinate two metal atoms. Catalysis for ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL), β‐butyrolactone (β‐BL), and lactide (LA) of complexes 1 and 2 was systematic studied. In combination with 9‐anthracenemethanol (9‐AnOH), Zn complex 1 was found to polymerize ε‐CL, β‐BL, and L‐LA with efficient catalytic activities in a controlled character. This study also compared the reactivity of these ROP monomers with different ring strains by Zn catalyst 1 in the presence of 9‐AnOH. Additionally, Zn complex 1 combining with benzoic acid was demonstrated to be an active catalytic system to copolymerize phthalic anhydride and cyclohexene oxide. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 714–725     

Cyclopentadienyl-ruthenium(II) complexes as efficient catalysts for the reduction of carbonyl compounds

This work reports the reduction of a large variety of aldehydes and ketones with the system PhSiH₃/[CpRu(PPh₃)₂Cl] in good to excellent yields and high chemoselectivity. The catalyst [CpRu(PPh₃)₂Cl] can be used in at least 12 catalytic cycles with excellent catalytic activity and several substrates were reduced under solvent free conditions.     

Bis(NHC)-Pd(II) complexes as highly efficient catalysts for allylation of aldehydes with allyltributyltin

Novel cis-chelated bidentate bis(NHC)-Pd(II) complexes derived from 1,1′-binaphthyl-2,2′-diamine (BINAM) bearing weakly coordinating acetate or trifluoroacetate counterions have been synthesized and their structures have been characterized by X-ray diffraction of single crystals. We found that these bis(NHC)-Pd(II) complexes were highly effective in the allylation of aldehydes with allyltributyltin to give the corresponding products in good to excellent yields in most cases at room temperature.     

Air‐stable copper derivatives as efficient catalysts for controlled lactide polymerization: Facile synthesis and characterization of well‐defined benzotriazole phenoxide copper complexes

Air‐stable copper catalysts supported by bis‐ BTP ligands ( BTP = N,O‐bidentate benzotriazole phenoxide) were synthesized and structurally characterized. The reactions of Cu(OAc)₂·H₂O with 2.0 molar equivalents of sterically bulky 2‐(2H‐benzotriazol‐2‐yl)‐4,6‐bis(1‐methyl‐1‐phenylethyl)phenol ( ^CMe2PhBTP ‐H) and 2‐(2H‐benzotriazol‐2‐yl)‐4,6‐di‐tert‐butylphenol ( ^t‐BuBTP ‐H) in refluxing ethanol solution afforded monomeric copper complexes [(^CMe2PhBTP)₂Cu] ( 1 ) and [(^t‐BuBTP)₂Cu] ( 2 ), respectively. The four‐coordinated copper analogue [(^TMClBTP)₂Cu] (3 ) resulted from treatment of 2‐tert‐butyl‐6‐(5‐chloro‐2H‐benzotriazol‐2‐yl)‐4‐methylphenol ( ^TMClBTP ‐H) as the ligand under the same synthetic method with ligand to metal precursor ratio of 2:1, but treatment of complex 3 in acetone gave five‐coordinated monomeric complex [(^TMClBTP)₂Cu(Me₂CO)] (4 ). X‐ray diffraction of single crystals indicates that Cu complex 4 assumes a distorted square pyramidal geometry, penta‐coordinated by two BTP ligands, and one Me₂CO molecule. Catalysis for lactide (LA) polymerization of BTP ‐containing Cu complexes in the presence of various alcohol initiators was investigated. Complex 3 initiated by 9‐anthracenemethanol catalyzes the ring‐opening polymerization effectively not only in a “living” fashion but also in an “immortal” manner, yielding polymers with the predictable molecular weights and narrow molecular weight distributions. Initiations from multifunctional alcohols were able to produce PLLAs with two‐arm linear and three‐arm star‐shaped molecular architectures. The controlled character of Cu complex 3 also enabled us to synthesize the PEG‐b‐PLLA copolymer. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3840–3849     

Vanadium(V) complexes containing tetradentate amine trihydroxy ligands as catalysts for copolymerization of cyclic olefins

A series of vanadium(V) complexes bearing tetradentate amine trihydroxy ligands [NOOO], which differ in the steric and electronic properties, have been synthesized and characterized. Single crystal X‐ray analysis showed that these complexes are five or six coordinated around the vanadium center in the solid state. Their coordination geometries are octahedral or trigonal bipyramidal. In the presence of Et₂AlCl, these complexes have been investigated as the efficient catalysts for ethylene polymerization and ethylene/norbornene copolymerization at elevated reaction temperature and produced the polymers with unimodal molecular weight distributions (MWDs), indicating the single site behaviors of these catalysts. Both the steric hindrance and electronic effect of the groups on the tetradentate ligands directly influenced catalytic activity and the molecular weights of the resultant (co)polymers. Other reaction parameters that influenced the polymerization behavior, such as reaction temperature, ethylene pressure, and comonomer concentration, are also examined in detail. Furthermore, high catalytic activities of up to 3.30 kg polymer/mmol_V·h were also observed when these complexes were applied to catalyze the copolymerization of ethylene and 5‐norbornene‐2‐methanol, producing the high‐molecular‐weight copolymers (M_w = 157–400 kg/mol) with unimodal MWDs (M_w/M_n = 2.5–3.0) and high polar comonomer incorporations (up to 12.3 mol %). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1122–1132, 2010     

Synthesis of highly reactive polyisobutylenes using solvent‐ligated manganese(II) complexes as catalysts

Manganese complexes with benzonitrile ligands were synthesized, characterized, and applied for the preparation of the isobutylene polymerization. Low and medium molecular weight polyisobutylenes containing high amount of exo‐type double bond end groups (70–80%) were successfully prepared using these manganese(II) complexes as catalysts at room temperature. The influence of monomer and catalyst concentration was intensively analyzed for achieving high monomer conversion and high exo double bond content of the products. Details on end group distribution in the products and development of the exo‐type end group content with reaction time were evaluated by ¹H NMR. The catalysts are also active for the homopolymerization of styrene and the copolymerization of isobutylene and styrene. The highly reactive polyisobutylene products obtained by these manganese complexes show features similar to products obtained by conventional cationic polymerization, but the polymerization characteristics clearly deviate. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5636–5648, 2007     

Bis(pyrazolyl)pyridine vanadium(III) complexes as highly active ethylene polymerization catalysts

The synthesis, characterization and catalytic activity in ethylene polymerization of novel mononuclear vanadium complexes bearing N^∧N^∧N-tridentate (pyrazolyl-pyridine) ligands are described. With AlEtCl₂ as co-catalyst, complexes 1 and 2 produce single-site catalysts that polymerized ethylene affording high density polyethylene with fairly narrow molecular weight distribution.     

Tridentate anilido‐aldimine magnesium and zinc complexes as efficient catalysts for ring‐opening polymerization of ε‐caprolactone and L‐lactide

A novel tridentate anilido‐aldimine ligand, [o‐C₆H₄(NHAr)? HC?NCH₂CH₂NMe₂] (Ar = 2,6‐ⁱPr₂C₆H₃, L ‐H, 1 ), has been prepared by the condensation of N, N‐dimethylethylenediamine with one molar equivalent of 2‐fluoro‐benzaldehyde in hexane, followed by the addition of the lithium salt of diisopropylaniline in THF. Magnesium (Mg) and zinc (Zn) complexes supported by the tridentate anilido‐aldimine ligand have been synthesized and structurally characterized. Reaction of L ‐H ( 1 ) with an equivalent amount of MgⁿBu₂ or ZnEt₂ produces the monomeric complex [ L MgⁿBu] ( 2 ) or [ L ZnEt] ( 3 ), respectively. Experimental results show that complexes 2 and 3 are efficient catalysts for ring‐opening polymerization of ε‐caprolactone (CL) and L ‐lactide (LA) in the presence of benzyl alcohol and catalyze the polymerization of ε‐CL and L ‐LA in a controlled fashion yielding polymers with a narrow polydispersity index. In both polymerizations, the activity of Mg complex 2 is higher than that of Zn complex 3 , which is probably due to the higher Lewis acidity and better oxophilic nature of Mg²⁺ metal. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4927–4936, 2009