Copolymerization of Carbon Dioxide and Propylene Oxide by Binary Cobalt Salen Complexes with Various Anion Groups

A series of salen–Co (III )(X) complexes tethering quaternary ammonium salts are designed to investigate the influence of the axial group X in the complex and the anion Y of quaternary ammonium salt on the copolymerization of CO₂ and PO . By copolymerization, the complex 9 , where X and Y are both 2,4‐dinitrophenolate, has the highest catalytic efficiency. When X is OAc and Y is BF₄ ⁻/NO₃ ⁻, the complexes 11/12 have lower catalytic efficiency. For the complex 10 , where X and Y are both OAc , the catalytic efficiency is the lowest. At the same time, complex 9 can produce the copolymer with the highest carbonate fraction and M _n. And the best copolymerization conditions were as follows: reaction temperature 30°C, copolymerization time 24 h, and CO₂ pressure 2 MPa with complex 9 . The thermal properties of the copolymers are also studied by differential scanning calorimetry (DSC) and thermogravimetry (TG) .     

Mechanistic insight into initiation and chain transfer reaction of CO2/cyclohexene oxide copolymerization catalyzed by zinc?cobalt double metal cyanide complex catalysts

Although zinc? cobalt (III) double metal cyanide complex (Zn? Co (III) DMCC) catalyst is a highly active and selective catalyst for carbon dioxide (CO₂)/cyclohexene oxide (CHO) copolymerization, the structure of the resultant copolymer is poorly understood and the catalytic mechanism is still unclear. Combining the results of kinetic study and electrospray ionization‐mass spectrometry (ESI‐MS) spectra for CO₂/CHO copolymerization catalyzed by Zn? Co (III) DMCC catalyst, we disclosed that (1) the short ether units were mainly generated at the early stage of the copolymerization, and were hence in the “head” of the copolymer and (2) all resultant PCHCs presented two end hydroxyl (? OH) groups. One end ? OH group came from the initiation of zinc? hydroxide (Zn? OH) bond and the other end ? OH group was produced by the chain transfer reaction of propagating chain to H₂O (or free copolymer). Adding t‐BuOH (CHO: t‐BuOH = 2:1, v/v) to the reaction system led to the production of fully alternating PCHCs and new active site of Zn? Ot‐Bu, which was proved by the observation of PCHCs with one end ? Ot‐Bu (and ? OCOOt‐Bu) group from ESI‐MS and ¹³C NMR spectra. Moreover, Zn?OH bond in Zn? Co (III) DMCC catalyst was also characterized by the combined results from FT‐IR, TGA and elemental analysis. This work provided new evidences that CO₂/CHO copolymerization was initiated by metal? OH bond. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Poly(Alkyl Glycidate Carbonate)s as Degradable Pressure‐Sensitive Adhesives

Insertion of CO₂ into the polyacrylate backbone, forming poly(carbonate) analogues, provides an environmentally friendly and biocompatible alternative. The synthesis of five poly(carbonate) analogues of poly(methyl acrylate), poly(ethyl acrylate), and poly(butyl acrylate) is described. The polymers are prepared using the salen cobalt(III) complex catalyzed copolymerization of CO₂ and a derivatized oxirane. All the carbonate analogues possess higher glass‐transition temperatures (T_g=32 to ?5 °C) than alkyl acrylates (T_g=10 to ?50 °C), however, the carbonate analogues (T_d≈230 °C) undergo thermal decomposition at lower temperatures than their acrylate counterparts (T_d≈380 °C). The poly(alkyl carbonates) exhibit compositional‐dependent adhesivity. The poly(carbonate) analogues degrade into glycerol, alcohol, and CO₂ in a time‐ and pH‐dependent manner with the rate of degradation accelerated at higher pH conditions, in contrast to poly(acrylate)s.     

Effect of supercritical CO2 on the copolymerization behavior of cyclohexene oxide/CO2 and copolymer properties with DMC/Salen‐Co(III) catalyst system

The copolymerization of cyclohexene oxide (CHO) and carbon dioxide (CO₂) was carried out under supercritical CO₂ (scCO₂) conditions to afford poly (cyclohexene carbonate) (PCHC) in high yield. The scCO₂ provided not only the C1 feedstock but also proved to be a very efficient solvent and processing aid for this copolymerization system. Double metal cyanide (DMC) and salen‐Co(III) catalysts were employed, demonstrating excellent CO₂/CHO copolymerization with high yield and high selectivity. Surprisingly, our use of scCO₂ was found to significantly enhance the copolymerization efficiency and the quality of the final polymer product. Thermally stable and high molecular weight (MW) copolymers were successfully obtained. Optimization led to excellent catalyst yield (656 wt/wt, polymer/catalyst) and selectivity (over 96% toward polycarbonate) that were significantly beyond what could be achieved in conventional solvents. Moreover, detailed thermal analyses demonstrated that the PCHC copolymer produced in scCO₂ exhibited higher glass transition temperatures (T_g ～ 114 °C) compared to polymer formed in dense phase CO₂ (T_g ～ 77 °C), and hence good thermal stability. Additionally, residual catalyst could be removed from the final polymer using scCO₂, pointing toward a green method that avoids the use of conventional volatile organic‐based solvents for both synthesis and work‐up. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2785–2793     

DFT studies on the origin of regioselective ring-opening of terminal epoxides during copolymerization with CO<Subscript>2</Subscript>

This report presents a detailed density functional theory（DFT） study on the difference in regioselectivity for the copolymerization reactions of styrene oxide versus propylene oxide with CO₂ utilizing binary（salen）cobalt（Ⅲ） catalyst systems. This study focuses on the discrepancy of regioselective ring-opening of two terminal epoxides during the copolymerization with CO₂. It was found that the nucleophilic ring-opening of styrene oxide occurred predominantly at the methine C_a―O bond due to the election delocalization of phenyl group to stabilize the transition state for the methine C―O bond cleavage.     

Study of electronic effect in bifunctional catalysts for the copolymerization of CO2 and PO/CHO

Carbon dioxide (CO₂) is an easily available renewable carbon source that can be used as a comonomer in the catalytic ring-opening polymerization of epoxides to form aliphatic polycarbonates. Herein, a series of new Salen-Co(III) bifunctional catalysts were synthesized for the first time, and they were studied to catalyze the copolymerization of CO₂ and propylene oxide (PO)/cyclohexene oxide (CHO). At the same time, the effects of reaction conditions (electronic effect, temperature, time) on catalytic activity and selectivity were investigated. The results show that the Salen-Co(III) complexes with electron-withdrawing groups have higher selectivity and activity for propylene carbonate (PPC)/cyclohexylene carbonate (PCHC). At the same time, the Salen-Co(III) complexes can better catalyze the copolymerization of CHO and CO₂ than that of PO and CO₂. The catalytic efficiency of the four complexes increased with increasing temperature, and the best reaction condition is 80°C, 30 min and 2 MPa of CO₂.     

Stereoregular polycarbonate synthesis: Alternating copolymerization of CO2 with aliphatic terminal epoxides catalyzed by multichiral cobalt(III) complexes

Completely stereoregular polycarbonate synthesis was achieved with the use of unsymmetric multichiral cobalt‐based complexes bearing a derived chiral BINOL and an appended 1,5,7‐triabicyclo[4.4.0] dec‐5‐ene as catalyst for the copolymerization of CO₂ and aliphatic terminal epoxides at mild conditions. The (S,S,S)‐Co(III) complex 1c with sterically hindered substituent group is more stereoregular catalyst for the copolymerization of CO₂ and racemic propylene oxide to afford a perfectly regioregular poly(propylene carbonate) (PPC), with >99% head‐to‐tail linkages, >99% carbonate linkages, and a K_rel of 24.4 for the enchainment of (R)‐epoxide over (S)‐epoxide. The isotactic PPC exhibits an enhanced glass transition temperature of 47 °C, which is 10–12 °C higher than that of the corresponding irregular polycarbonate. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Concerning the Deactivation of Cobalt(III)‐Based Porphyrin and Salen Catalysts in Epoxide/CO2 Copolymerization

Functioning as active catalysts for propylene oxide (PO) and carbon dioxide copolymerization, cobalt(III)‐based salen and porphyrin complexes have drawn great attention owing to their readily modifiable nature and promising catalytic behavior, such as high selectivity for the copolymer formation and good regioselectivity with respect to the polymer microstructure. Both cobalt(III)–salen and porphyrin catalysts have been found to undergo reduction reactions to their corresponding catalytically inactive cobalt(II) species in the presence of propylene oxide, as evidenced by UV/Vis and NMR spectroscopies and X‐ray crystallography (for cobalt(II)–salen). Further investigations on a TPPCoCl (TPP=tetraphenylporphyrin) and NaOMe system reveal that such a catalyst reduction is attributed to the presence of alkoxide anions. Kinetic studies of the redox reaction of TPPCoCl with NaOMe suggests a pseudo‐first order in cobalt(III)–porphyrin. The addition of a co‐catalyst, namely bis(triphenylphosphine)iminium chloride (PPNCl), into the reaction system of cobalt(III)–salen/porphyrin and PO shows no direct stabilizing effect. However, the results of PO/CO₂ copolymerization by cobalt(III)–salen/porphyrin with PPNCl suggest a suppressed catalyst reduction. This phenomenon is explained by a rapid transformation of the alkoxide into the carbonate chain end in the course of the polymer formation, greatly shortening the lifetime of the autoreducible PO‐ring‐opening intermediates, cobalt(III)–salen/porphyrin alkoxides.     

Synthesis and characterization of Co (III) salen complex immobilized on cobalt ferrite‐silica nanoparticle and their application in the synthesis of spirooxindoles

The preparation, characterization and catalytic application of Co (III) salen complex loaded on cobalt ferrite‐silica nanoparticle [CoFe₂O₄@SiO₂@ Co (III) salen complex] are described. Co (III) salen complex loaded on ferrite cobalt‐silica nanoparticles is characterized by transmission electron microscopy, scanning electron microscopy coupled with energy‐dispersive X‐ray, vibrating‐sample magnetometer and Fourier transform‐infrared analyses. The thermal stability of the material is also determined by thermal gravimetric analysis. An average crystallite size is determined from the full‐width at half‐maximum of the strongest reflection by using Scherrer's approximation by powder X‐ray diffractometry. The efficiency of CoFe₂O₄@SiO₂@Co (III) salen complex is investigated in the synthesis of spirooxindoles of malononitrile, various isatins with 1,3‐dicarbonyles. The nanocatalyst demonstrated excellent catalytic activity that gave the corresponding coupling products in good to excellent yields. Moreover, the recoverability and reusability of CoFe₂O₄@SiO₂@Co (III) salen complex is investigated where nanocatalyst could be recovered and reused at least five times without any appreciable decrease in activity and selectivity, which confirmed its high efficiency and high stability under the reaction conditions and during recycling stages.     

CoFe2O4@SiO2@ Co (III) salen complex nanoparticle as a green and efficient magnetic nanocatalyst for the oxidation of benzyl alcohols by molecular O2

In the presence of cobalt (III) salen complex, selective oxidation of alcohols to carbonyl compounds was studied by molecular oxygen using isobutyraldehyde as an oxygen acceptor. The effect of cobalt (III) salen complex in the oxidation reaction was studied, and the results showed that Co (III) salen complex is very active and selective in the oxidation of various alcohols. Also, the effect of important factors including catalyst amount, solvent and temperature was investigated on the reaction. Furthermore, the catalytic activities of CoFe₂O₄@SiO₂‐supported Schiff base metal complex as well as the effect of molecular oxygen (O₂) as a green oxidant were studied. The results showed that benzaldehyde was the major product and the heterogeneous catalyst was highly reusable.     

Efficient solvent‐free alternating copolymerization of CO2 with 1, 2‐epoxydodecane and terpolymerization with styrene oxide via heterogeneous catalysis

The alternating copolymerization of CO₂ with the terminated epoxides anchoring long alkyl groups is rarely reported because of their low reactivity and polycarbonate selectivity. This work describes a well‐controlled solvent‐free copolymerization of CO₂ with 1, 2‐epoxydodecane (EDD) with a long electron‐donating alkyl group via the catalysis of Zn‐Co(III) double metal cyanide complex catalyst. The productivity of the catalyst was up to 2406 g polymer/g Zn, that is, EDD conversion was 99.2%. The alternating degree of CO₂‐EDD copolymers were more than 99% and had high number‐average molecular weights (M_ns) of >100 kg mol^?1, while only 1.0 wt % 4‐decyl‐1,3‐dioxolan‐2‐one (DC) were detected. Moreover, by introducing styrene oxide (SO) with electron‐withdrawing phenyl group into EDD‐CO₂ copolymerization system, a new random terpolymer with either electron‐withdrawing or electron‐donating side groups was produced with single glass transition temperatures (T_gs) in a wide range from 3 to 56 °C, which might be potentially used as biodegradable elastomers or plastics. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 737–744     

Ionic Polymer Microspheres Bearing a CoIII–Salen Moiety as a Bifunctional Heterogeneous Catalyst for the Efficient Cycloaddition of CO2 and Epoxides

We report a unique strategy to obtain the bifunctional heterogeneous catalyst TBB‐Bpy@Salen‐Co (TBB=1,2,4,5‐tetrakis(bromomethyl)benzene, Bpy=4,4’‐bipyridine, Salen‐Co=N,N’‐bis({4‐dimethylamino}salicylidene)ethylenediamino cobalt(III) acetate) by combining a cross‐linked ionic polymer with a Co^III–salen Schiff base. The catalyst showed extra high activity for CO₂ fixation under mild, solvent‐free reaction conditions with no requirement for a co‐catalyst. The synthesized catalyst possessed distinctive spherical structural features, abundant halogen Br^? anions with good leaving group ability, and accessible Lewis acidic Co metal centers. These unique features, together with the synergistic role of the Co and Br^? functional sites, allowed TBB‐Bpy@Salen‐Co to exhibit enhanced catalytic conversion of CO₂ into cyclic carbonates relative to the corresponding monofunctional analogues. This catalyst can be easily recovered and recycled five times without significant leaching of Co or loss of activity. Moreover, based on our experimental results and previous work, a synergistic cycloaddition reaction mechanism was proposed.     

Effect of Nano‐support and Type of Active Metal on Reforming of CH4 with CO2

Two series of Co and Ni based catalysts supported over commercial (ZrO₂, CeO₂, and Al₂O₃) nano supports were investigated for dry reforming of methane. The catalytic activity of both Co and Ni based catalysts were assessed at different reaction temperatures ranging from 500—800 °C; however, for stability the time on stream experiments were conducted at 700 °C for 6 h. Various techniques such as N₂ adsorption‐desorption isotherm, temperature‐programmed reduction (H₂‐TPR), temperature‐programmed desorption (CO₂‐TPD), temperature‐programmed oxidation (TPO), X‐ray diffraction (XRD), thermogravimetric analysis (TGA) were applied for characterization of fresh and spent catalysts. The catalytic activity and stability tests clearly showed that the performance of catalyst is strongly dependent on type of active metal and support. Furthermore, active metal particle size and Lewis basicity are key factors which have significant influence on catalytic performance. The results indicated that Ni supported over nano ZrO₂ exhibited highest activity among all tested catalysts due to its unique properties including thermal stability and reducibility. The minimum carbon deposition and thus relatively stable performance was observed in case of Co‐Al catalyst, since this catalyst has shown highest Lewis basicity.     

Poly(styrene)‐Supported Co–Salen Complexes as Efficient Recyclable Catalysts for the Hydrolytic Kinetic Resolution of Epichlorohydrin

Here we describe an unprecedented synthetic approach to poly(styrene)‐supported chiral salen ligands by the free radical polymerization of an unsymmetrical styryl‐substituted salen monomer (H₂salen=bis(salicylidene)ethylenediamine). The new method allows for the attachment of salen moieties to the polymer main chain in a flexible, pendant fashion, avoiding grafting reactions that often introduce ill‐defined species on the polymers. Moreover, the loading of the salen is controlled by the copolymerization of the styryl‐substituted salen monomer with styrene in different ratios. The polymeric salen ligands are metallated with cobalt(II ) acetate to afford the corresponding supported Co–salen complexes, which are used in the hydrolytic kinetic resolution of racemic epichlorohydrin, exhibiting high reactivity and enantioselectivity. Remarkably, the copolymer‐supported Co–salen complexes showed a better catalytic performance (>99 % ee, 54 % conversion, one hour) in comparison to the homopolymeric analogues and the small molecule Co–salen complex. The soluble poly(styrene)‐supported catalysts were recovered by precipitation after the catalytic reactions and were recycled three times to afford almost identical enantiomeric excesses as the first run, with slightly reduced reaction rates.     

(Salan)CrCl,an effective catalyst for the copolymerization and terpolymerization of epoxides and carbon dioxide

The selective transformation of CO₂ and epoxides to afford completely alternating copolymers remains a topic of much interest for the potential utilization of carbon dioxide in chemical synthesis. The use of salicylaldimine (salen)‐metal complexes and their saturated (salan)‐metal versions have proven to be the most effective and robust single‐site catalyst for these processes. Herein, we report on mechanistic aspects of the copolymerization of alicyclic and aliphatic epoxides with CO₂ in toluene solution and in neat epoxides in the presence of a (salan)CrCl/onium salt catalyst system. The activation barriers for both cyclohexene oxide(CHO)/CO₂ and propylene oxide(PO)/CO₂ were shown to be significantly higher in toluene solution than those previously reported for reactions carried out under solventless conditions. Terpolymerization of CHO/vinylcyclohexene oxide/CO₂ was shown via Fineman‐Ross analysis at 60 °C to proceed with little monomer selectivity, for example, r_CHO = 1.03 and r_VCHO = 0.847. On the other hand, terpolymerization of CHO/PO/CO₂ occurred at 25 °C with a propensity for incorporation of PO in the polymer. However, at 40 °C, Fineman‐Ross analysis revealed r_CHO and r_PO values of 0.869 and 1.49, thereby affording a terpolymer with a more equal distribution of monomers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Alternating copolymerization of carbon dioxide and epoxide catalyzed by an aluminum Schiff base–ammonium salt system

The alternating copolymerization of carbon dioxide (CO₂) and cyclohexene oxide (CHO) with an aluminum Schiff base complex in conjunction with an appropriate additive as a novel initiator is demonstrated. A typical example is the copolymerization of CO₂ and CHO with the (Salophen)AlMe ( 1a )–tetraethylammonium acetate (Et₄NOAc) system. When a mixture of the 1a –Et₄NOAc system and CHO was pressurized by CO₂ (50 atm) at 80 °C in CH₂Cl₂, the copolymerization of CO₂ and CHO took place smoothly and produced a high polymer yield in 24 h. From the IR and NMR spectra, the product was characterized to be a copolymer of CO₂ and CHO with an almost perfect alternating structure. The matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis indicated that an unfavorable reaction between Et₄NOAc and CH₂Cl₂ and a possible chain‐transfer reaction with concomitant water occurred, and this resulted in the bimodal distribution of the obtained copolymer. With carefully predried reagents and apparatus, the alternating copolymerization in toluene gave a copolymer with a unimodal and narrower molecular weight distribution. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4172–4186, 2005     

Electrosynthesis of 2‐Arylpropionic Acids from α‐Methylbenzyl Chlorides and Carbon Dioxide by [Co(Salen)]

Abstract

The electrochemical synthesis of the 2‐arylpropionic acid group of nonsteroidal anti‐inflammatory agents such as ibuprofen, naproxen, indoprofen, biprofen, cicloprofen, and fenoprofen has been carried out in dimethylformamide (DMF) containing tetra‐n‐butylammonium perchlorate (nBu₄NClO₄) by electrochemical carboxylation of α‐methylbenzyl chlorides catalyzed by a schiff‐base complex [Co(salen)] in an undivided cell equipped with a platinum cathode and magnesium anode under constant current density of 10 mA/cm² in good yields. Cyclic voltammetric studies have also been carried out to investigate the mechanism by which [Co(salen)] catalyzes the cathodic reaction of α‐methylbenzyl chlorides in presence of CO₂ by taking α‐phenylethylchloride as the model compound.     

Anionic Copolymerization of Carbonyl Sulfide with Epoxides via Alkali Metal Alkoxides

Carbonyl sulfide (COS), an analogue of carbon dioxide (CO₂), can be converted to CO₂ via the carbonic anhydride enzymes widely existing in nature. COS is an ideal monomer for making poly(monothiocarbonate)s, which are difficult to synthesize by traditional methods. Herein, for the first time, we describe an anionic copolymerization of COS with epoxides using alkali metal alkoxides as the catalysts (initiators), affording poly(monothiocarbonate)s with 100% alternating degree, >99% tail‐to‐head (T‐H) content, high number‐average molecular weights (M_ns, up to 90.3 kg/mol) with narrow molecular weight distributions (Đ=M_w/M_n, 1.05—1.31 for COS/propylene oxide copolymers) under solvent‐free and mild conditions. Oxygen‐sulfur exchange reaction (O/S ER), which can result in the production of contaminated dithiocarbonate and carbonate units in the main chain, was nearly completely depressed at 0 ^oC. In addition, in contrast to previously reported salen chromium (iron) complexes that required multiple synthetic steps, this work provides simple, low‐cost, and effective catalysts for making colorless sulfur‐containing polymers.     

Effect of the ligand nature in cobalt complexes on the selectivity of the reaction of carbon dioxide and propylene oxide

The reaction of carbon dioxide with propylene oxide in the presence of the (salen)CoCl or (TPP)CoCl (salen = bis(3,5-di-tert-butyl-salicylidene)-1,2-diaminocyclohexane, TPP = 5,10,15,20-tetraphenylporphyrin) catalyst and the PPNCl (bis(triphenylphosphine)iminium chloride) cocatalyst has been carried out at 20–60°С and a СО₂ pressure of 0.6 MPa to investigate the effect of the ligand nature on the reaction rate and selectivity. The change in the reaction rate and selectivity in relation to the temperature and cocatalyst/catalyst ratio has been studied. The activation energy of the copolymerization of СО₂ with propylene oxide catalyzed by the (salen)CoCl complex have been obtained.     

Thermal and pH responsive high molecular weight poly(urethane‐amine) with high urethane content

Aliphatic poly(urethane‐amine) (PUA) was synthesized from copolymerization of CO₂ and 2‐methylaziridine (MAZ) using Y(CCl₃COO)₃‐ZnEt₂‐glycerine coordination catalyst, the urethane content of PUA was over 80%, and its yield could reach 90%. PUA with molecular weight as high as 31.0 kg/mol was obtained when the copolymerization reaction was carried out in N,N‐dimethylacetamide (DMAc), mainly due to the good solubility of PUA in DMAc. PUA exhibited reversible thermo‐responsive property in deionized water, and the lower critical solution temperature (LCST) was highly sensitive to its urethane content and molecular weight, which was observed in a broad window from 37 to 90 °C. Furthermore, the phase transition behavior could also be controlled by change of pH value. When the pH value of the PUA aqueous solution changed from 9.2 to 13, the LCST value of the solution decreased from 48.4 °C to 30 °C. Therefore, the PUA showed thermo‐ and pH‐ dual responsive performance in water. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011