Steric hindrance ligand strategy to aluminum porphyrin catalyst for completely alternative copolymerization of CO2 and propylene oxide

Aluminum porphyrin complexes are heavy-metal-free and soil-tolerant green catalysts for the copolymerization of CO2 and propylene oxide (PO),but they suffer from relatively poor poly(propylene carbonate) (PPC) selectivity.Herein,steric hindrance porphyrin ligand was used to enhance the PPC selectivity.Typically,a bulky anthracene-like group was incorporated into the porphyrin ring to form 5,10,15,20-tetra(1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracen-9-yl)porphyrin,the aluminum porphyrin complex with this ligand,in combination with bis(triphenylphosphine)iminium chloride as a co-catalyst,produced completely alternate PPC.Additionally,the obtained PPC showed high regioselectivity,with a head-to-tail linkage content (HT) of 92％.Therefore,we demonstrated that introduction of bulky steric ligand into the porphyrin ring could reduce the propylene oxide homopolymerization activity leading to excellent PPC selectivity,and improve regioselectivity for the PO ring-opening during the copolymerization.     

Inside Cover: Temperature‐responsive Catalyst for the Coupling Reaction of Carbon Dioxide and Propylene Oxide (Chin. J. Chem. 4/2018)

The inside cover picture shows a temperature controllable porphyrin aluminum catalyst using 5,10,15,20‐tetra(1,2,3,4,5,6,7,8‐octahydro‐1,4:5,8‐dimethanoanthracen‐9‐yl)porphyrin as ligand, which showed significantly temperature‐responsive selectivity in the coupling reaction of CO₂ and PO. Only cycloaddition reaction happened at temperature above 75 °C to produce 100% CPC, whereas copolymerization became dominant to afford PPC with selectivity over 91% at temperature below 50 °C. More details are discussed in the article by Wang et al. on page 299–305.

     

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.     

Fixation of carbon dioxide into aliphatic polycarbonate,cobalt porphyrin catalyzed regio‐specific poly(propylene carbonate) with high molecular weight

Cobalt porphyrin complex (TPPCo^IIIX) (TPP = 5, 10, 15, 20‐Tetraphenyl‐ porphyrin; X = halide) in combination with ionic organic ammonium salt was used for the regio‐specific copolymerization of propylene oxide and carbon dioxide. A turnover frequency of 188 h^?1 was achieved after 5 h, and the byproduct propylene carbonate was successfully controlled to below 1%, where the obtained poly(propylene carbonate) (PPC) showed number average molecular weight (M_n) of 48 kg/mol, head‐to‐tail content of 93%, and carbonate linkage of over 99%. When the polymerization time was prolonged to 24 h, PPC with M_n over 115 kg/mol and head‐to‐tail linkage maintaining 90% was prepared, whose glass transition temperature reached 44.5 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5959–5967, 2008     

Regio‐regular structure high molecular weight poly(propylene carbonate) by rare earth ternary catalyst and Lewis base cocatalyst

Lewis base modification strategy on rare earth ternary catalyst was disclosed to enhance nucleophilic ability of active center during copolymerization of carbon dioxide and propylene oxide (PO), poly(propylene carbonate) (PPC) with H‐T linkages over 83%, and number–average molecular weight (M_n) up to 100 kg/mol was synthesized at room temperature using Y(CCl₃OO)₃‐ZnEt₂‐glycerine catalyst and 1,10‐phenanthroline (PHEN) cocatalyst. Coordination of PHEN with active Zinc center enhanced the nucleophilic ability of the metal carbonate, which became more regio‐specific in attacking carbon in PO, leading to PPC with improved H‐T linkages. Moreover, the binding of PHEN to active Zinc center also raised the carbonate content of PPC to over 99%, whereas the PPC from common rare earth ternary catalyst was about 96%. Unlike the highly regio‐regular structure PPC but with relatively low molecular weight recently reported in the literature, our high molecular weight regio‐regular PPC did show significant improvement in thermal and mechanical performances. PPC with H‐T linkages up to 83.2% showed glass transition temperature (T_g) of 43.3 °C, while T_g of PPC with H‐T linkages of 69.7% was only 36.1 °C. When H‐T connectivity was raised from 69.7 to 83.2%, the modulus of PPC showed a 78% increase. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4451–4458, 2008     

Bifunctional aluminum porphyrin complex: Soil tolerant catalyst for copolymerization of 2 and propylene oxide

Due to the concern on residue toxic metal in biodegradable poly(propylene carbonate) (PPC), soil tolerant and heavy metal free aluminum complexes, that is, bifunctional aluminum porphyrin catalysts bearing quaternary ammonium salts on the ligand framework were prepared. Variation of the quaternary ammonium anion and the axial ligand had dramatic effects on the catalytic activity of resultant complex, among which complex 3b yielded perfectly alternative PPC with high molecular weight and relatively narrow polydispersity, and its TOF reached 3,407 h^?1 at [PO]/[cat.] ratio of 20,000 at 110 °C, although the PPC selectivity was 71%. By introducing specific substituent on the ligand framework, the electronic environment at the active center can be changed, among which complex 5b bearing tertiary butyl‐functionalized aryl substituents exhibited a TOF of 449 h^?1 at [PO]/[cat.] ratio of 5,000 at 70 °C, with PPC selectivity of 92% and number average molecular weight of 36 kg mol^?1. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2346–2355     

铝卟啉配合物催化二氧化碳与环氧丙烷共聚反应

铝卟啉是一类土壤环境友好的金属卟啉,尽管早在1978年Inoue就已经发现它可以催化CO₂和环氧丙烷的共聚反应,但是该催化体系一直面临催化活性低、聚合物相对分子质量低等难题。 本文通过改变铝卟啉催化剂配体中苯环上取代基的种类和位置,制备出中心金属电子环境差异化的铝卟啉,并以双三苯基膦氯化铵(PPNCl)为助催化剂,探讨其对CO₂与环氧丙烷的共聚反应的催化行为。 结果表明,当铝卟啉中苯环上2,4位同时被Cl^-取代后,在90 ℃和3 MPa压力下,转化频率(TOF)达到2672 h^-1。 当利用离去能力较强的对甲苯磺酸基团(OTs^-)作为铝卟啉的轴向配体,可以合成出数均相对分子质量达1.84×10⁵的脂肪族聚碳酸酯。     

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.     

Correlating Metal Redox Potentials to Co(III)K(I) Catalyst Performances in Carbon Dioxide and Propene Oxide Ring Opening Copolymerization

Carbon dioxide copolymerization is a front-runner CO₂ utilization strategy but its viability depends on improving the catalysis. So far, catalyst structure-performance correlations have not been straightforward, limiting the ability to predict how to improve both catalytic activity and selectivity. Here, a simple measure of a catalyst ground-state parameter, metal reduction potential, directly correlates with both polymerization activity and selectivity. It is applied to compare performances of 6 new heterodinuclear Co(III)K(I) catalysts for propene oxide (PO)/CO₂ ring opening copolymerization (ROCOP) producing poly(propene carbonate) (PPC). The best catalyst shows an excellent turnover frequency of 389 h⁻¹ and high PPC selectivity of >99 % (50 °C, 20 bar, 0.025 mol% catalyst). As demonstration of its utility, neither DFT calculations nor ligand Hammett parameter analyses are viable predictors. It is proposed that the cobalt redox potential informs upon the active site electron density with a more electron rich cobalt centre showing better performances. The method may be widely applicable and is recommended to guide future catalyst discovery for other (co)polymerizations and carbon dioxide utilizations.     

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 of Cyclic Carbonate Catalyzed by DBU Derived Basic Ionic Liquids

In this work, 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU), 1,5‐diazabicyclo[4.3.0]‐5‐nonene (DBN), and imidazole (MIM)‐derived bromide ionic liquids (ILs) were synthesized and used to catalyze the cycloaddition reactions of carbon dioxide (CO₂) with several kinds of epoxides to form cyclic carbonates. The DBU derived bromide ionic liquid system was found to have the best catalytic activity among all the tested ILs. The influences of reaction conditions (including temperature, pressure and reaction time) on the reaction of CO₂ to propylene oxide (PO) were studied to show the best conditions of 120 °C, 1 MPa, 2.5 h catalyzed by 2 mol% DBU‐derived bromide ionic liquid, with the conversion of PO and the selectivity of propylene carbonate (PC) reaching 99% and 99%, respectively. Under the optimum reaction conditions, the ionic liquid system could be reused at least five times without decrease in selectivity and conversion. NMR spectroscopy and DFT calculations were used to reveal the hydrogen‐bond interaction between ionic liquids and reagent, based on which the reaction mechanism was proposed.     

Titanocene dichloride/KI: an efficient catalytic system for synthesis of cyclic carbonates from epoxides and CO2

Titanocene dichloride (Cp₂TiCl₂)/KI was developed to be an efficient catalytic system for the cycloaddition of CO₂ to epoxides to synthesize relevant cyclic carbonates from epoxides and CO₂. Various influencing factors on the coupling reaction, such as co‐catalyst, temperature, CO₂ pressure and reaction time, were investigated. The optimal reaction conditions were KI as co‐catalyst, 150 °C reaction temperature, 12 atm CO₂ pressure and 4 h reaction time using THF as solvent for the synthesis of propylene carbonate in 98% yield. Copyright © 2013 John Wiley & Sons, Ltd.     

高分子量二氧化碳-环氧丙烷共聚物的合成条件研究

利用新型多配体负载戊二酸锌来催化二氧化碳和环氧丙烷合成高分子量聚碳酸(1,2-丙二醇).通过研究反应时间和反应压力对产率以及产物的结构和性能的影响来对反应条件进行了优化.结果表明在反应压力为5.2MPa,反应时间为40h时所得聚合物的数均分子量大于23×104,玻璃化转变温度达到38℃,拉伸强度达到31MPa.     

Cycloaddition of epoxide and CO2 to cyclic carbonate catalyzed by VO(IV) porphyrin

The cycloaddition of epoxide and CO₂ to synthesize cyclic carbonate catalyzed by VO(IV) porphyrin was achieved under 1.4 MPa at 150°C. The effects of reaction temperature, time, CO₂ pressure, co‐catalyst and porphyrin framework were investigated. The catalytic results showed that moderate to high yields of cyclic carbonates were obtained under the optimal reaction conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

Copolymerization of carbon dioxide and propylene oxide by several metallosalen‐based bifunctional catalysts

A series of new metallosalen‐based bifunctional catalysts with Co(III), Cr(III), Fe(III), Mn(III), and Ni(III) were synthesized for the first time, and a detailed study on the mechanism of the copolymerization of CO₂ and propylene oxide (PO) was performed. Meanwhile, the impact factors of the reaction conditions (metal cations, temperature, CO₂ pressure, and reaction time) on catalytic activity and selectivity were investigated. The results indicated that, with the increase of temperature, both the catalyst efficiency and the molecular weight of the copolymer decrease for all the five complexes. The salen‐Co(III) complex demonstrated higher activity under mild conditions: reaction temperature at 30 °C, copolymerization time of 24 hr, and 2 MPa of CO₂ pressure. The DSC curve indicated that the PPC by the salen‐Co(III) complex has the highest T_g of 46.19 °C. DTGA curves demonstrated that there were two thermal degradation peaks: the first is for the ester bond, and the second is for the C C bond.     

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.     

Regarding Initial Ring Opening of Propylene Oxide in its Copolymerization with CO2 Catalyzed by a Cobalt(III) Porphyrin Complex

Cobalt(III) tetraphenylporphyrin chloride (TPPCoCl) was experimentally proved to be an active catalyst for poly(propylene carbonate) production. It was chosen as a model catalyst in the present work to investigate the initiation step of propylene oxide (PO)/CO₂ copolymerization, which is supposed to be the ring opening of the epoxide. Ring‐opening intermediates ( 1 – 7 ) were detected by using ¹H NMR spectroscopy. A first‐order reaction in TPPCoCl was determined. A combination of monometallic and bimetallic ring‐opening pathways is proposed according to kinetics experiments. Addition of onium salts (e.g., bis(triphenylphosphine)iminium chloride, PPNCl) efficiently promoted the PO ring‐opening rate. The existence of axial ligand exchange in the cobalt porphyrin complex in the presence of onium salts was suggested by analyzing collected ¹H NMR spectra.     

聚合物负载季鏻盐催化 CO2 与环氧化物的环加成反应

 制备了聚合物负载的季鏻盐催化剂, 并用于 CO₂ 与环氧氯丙烷环加成反应中. 采用红外光谱、热分析、原子吸收光谱和扫描电子显微镜等手段测定了催化剂的结构、热性能、磷元素含量和表面形貌等. 考察了 CO₂ 压力、温度、催化剂用量和反应时间等对环加成反应性能的影响. 结果表明, 在催化剂用量为 0.09 g, CO₂ 压力为 4.5 MPa, 于 150 ^oC 反应 6 h 时, 3-氯甲基环碳酸酯收率可达 97.7%, 选择性大于 99%. 且催化剂易分离回收, 重复使用 5 次后产物收率和选择性没有明显下降. 同时探讨了该催化剂上 CO₂ 环加成合成环碳酸酯的可能机理.     

Cobalt catalysts for the alternating copolymerization of propylene oxide and carbon dioxide: combining high activity and selectivity

Synthetic pathways to (salcy)CoX (salcy = N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminocyclohexane; X = halide or carboxylate) complexes are described. Complexes (R,R)-(salcy)CoCl, (R,R)-(salcy)CoBr, (R,R)-(salcy)CoOAc, and (R,R)-(salcy)CoOBzF(5) (OBzF(5) = pentafluorobenzoate) are highly active catalysts for the living, alternating copolymerization of propylene oxide (PO) and CO(2), yielding poly(propylene carbonate) (PPC) with no detectable byproducts. The PPC generated using these catalyst systems is highly regioregular and has up to 99% carbonate linkages with a narrow molecular weight distribution (MWD). Inclusion of the cocatalysts [PPN]Cl or [PPN][OBzF(5)] ([PPN] = bis(triphenylphosphine)iminium) with complex (R,R)-(salcy)CoCl, (R,R)-(salcy)CoBr, or (R,R)-(salcy)CoOBzF(5) results in remarkable activity enhancement of the copolymerization as well as improved stereoselectivity and regioselectivity with maximized reactivity at low CO(2) pressures. In the case of [PPN]Cl with (R,R)-(salcy)CoOBzF(5), an unprecedented catalytic activity of 620 turnovers per hour is achieved for the copolymerization of rac-PO and CO(2), yielding iso-enriched PPC with 94% head-to-tail connectivity. The stereochemistry of the monomer and catalyst used in the copolymerization has dramatic effects on catalytic activity and the PPC microstructure. Using catalyst (R,R)-(salcy)CoBr with (S)-PO/CO(2) generates highly regioregular PPC, whereas using (R)-PO/CO(2) with the same catalyst gives an almost completely regiorandom copolymer. The rac-PO/CO(2) copolymerization with catalyst rac-(salcy)CoBr yields syndio-enriched PPC, an unreported PPC microstructure. In addition, (R,R)-(salcy)CoOBzF(5)/[PPN]Cl copolymerizes (S)-PO and CO(2) with a turnover frequency of 1100 h(-1), an activity surpassing that observed in any previously reported system.     

含桥式硫原子双酚盐配体的有机铋配合物的合成及其对CO2和环氧丙烷环加成反应催化性能的研究

合成分析了含有桥式硫原子二酚盐配体的新型有机铋配合物,并发现它们在亲核试剂(I-)存在下对CO2和环氧丙烷环加成反应合成碳酸丙烯酯表现出很高的催化活性和选择性.