A One‐Step Route to CO2‐Based Block Copolymers by Simultaneous ROCOP of CO2/Epoxides and RAFT Polymerization of Vinyl Monomers

The one‐step synthesis of well‐defined CO₂‐based diblock copolymers was achieved by simultaneous ring‐opening copolymerization (ROCOP) of CO₂/epoxides and RAFT polymerization of vinyl monomers using a trithiocarbonate compound bearing a carboxylic group (TTC‐COOH) as the bifunctional chain transfer agent (CTA). The double chain‐transfer effect allows for independent and precise control over the molecular weight of the two blocks and ensures narrow polydispersities of the resultant block copolymers (1.09–1.14). Notably, an unusual axial group exchange reaction between the aluminum porphyrin catalyst and TTC‐COOH impedes the formation of homopolycarbonates. By taking advantage of the RAFT technique, it is able to meet the stringent demand for functionality control to well expand the application scopes of CO₂‐based polycarbonates.     

A Biomass-Ligand-Based Ru(III) Complex as a Catalyst for Cycloaddition of CO2 and Epoxides to Cyclic Carbonates and a Study of the Mechanism

Aiming highly efficient conversion of greenhouse gas CO₂ to cyclic carbonates, a biomass Ru(III) Schiff base complex catalyst ( SalRu ) was constructed by employing a derivative of Lignin degradation (5-aldehyde vanillin). The SalRu catalyst had a remarkable conversion for epoxides into corresponding cyclic carbonates even at atmospheric pressure of CO₂ without the presence of co-catalyst. As the condition at 120 °C and 2 MPa CO₂ the conversion reached to 94 % with selectivity at 99 % after 8 h. 32 % cyclic carbonate production was obtained even under 0.2 MPa CO₂ pressure. The epoxide activation and ring opening, CO₂ insertion and cyclic carbonate formation were illuminated explicitly through the of characteristic absorption peaks changing, which further providing direct and visual evidence for the mechanism proposing. This study has important theoretical significance for the comprehensive utilization of environmental pollutants and energy.     

Triazine‐based Organic Polymer‐catalysed Conversion of Epoxide to Cyclic Carbonate under Ambient CO2 Pressure

In this work we have achieved epoxide to cyclic carbonate conversion using a metal‐free polymeric catalyst under ambient CO₂ pressure (1.02 atm) using a balloon setup. The triazine containing polymer (CYA‐ANIS) was prepared from cyanuric chloride (CYA?Cl) and o‐dianisidine (ANIS) in anhydrous DMF as solvent by refluxing under the N₂ gas environment. The presence of triazine and amine functional groups in the polymer results in the adsorption of CO₂ up to 7 cc/g at 273 K. This inspired us to utilize the polymer for the conversion of a series of functionalised epoxides into their corresponding cyclic carbonates in the presence of tetrabutyl ammonium iodide (TBAI) as co‐catalyst. The product has wide range of applications like solvent in lithium ion battery, precursor for polycarbonate, etc. The catalyst was efficient for the conversion of different mono and di‐epoxides into their corresponding cyclic carbonates under atmospheric pressure in the presence of TBAI as co‐catalyst. The study indicates that epoxide attached with electron withdrawing groups (like, CH₂Cl, glycidyl ether, etc.) displayed better conversion compared to simple alkane chain attached epoxides. This is mainly due to the stabilization of electron rich intermediates produced during the reaction (e. g. epoxide ring opening or CO₂ incorporation into the halo‐alkoxide anion). This catalyst mixture was capable to maintain its reactivity up to five cycles without losing its activity. Post catalytic characterization clearly supports the heterogeneous and recyclable nature of the catalyst.     

Cobalt(III)‐complex‐mediated terpolymerization of CO2, styrene oxide,and epoxides with an electron‐donating group

Terpolymerizations of CO₂, styrene oxide (SO), and epoxides with an electron‐donating group such as propylene oxide (PO) or cyclohexene oxide (CHO) were carried out by using Co(III)–salen complexes in the presence of an intra‐ or intermolecular nucleophilic cocatalyst. The resultant terpolymers have only one thermolysis peak and one glass transition temperature (T_g), which can be easily adjusted by controlling the proportion of styrene carbonate linkages. During the CO₂/SO/PO terpolymerization, the monomer reactivity ratios (r_SO = 0.18 and r_PO = 2.25) evaluated by Fineman–Ross plot indicates a random distribution of the two kinds of carbonate units in the resultant polymer. Contrarily, the monomer reactivity ratios were found to be r_SO = 0.48 and r_CHO = 0.79 in the CO₂/SO/CHO terpolymerization, indicating that an alternating nature of the two different carbonate units predominantly exists in the resultant polycarbonate. The regioselective ring opening of SO has a significant effect on the reactivities of both SO and CHO during the terpolymerization with CO₂. The matched reactivity is contributed to the enhanced regioselective ring opening of SO, caused by the attack of the dissociating polymer carboxylate anion, bearing a cyclohexene carbonate end unit. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Amino acids/superbases as eco-friendly catalyst system for the synthesis of cyclic carbonates under metal-free and halide-free conditions

An eco-friendly and efficient binary catalyst system of superbases and amino acids was developed for the synthesis of cyclic carbonates from epoxides and CO₂ under metal-free and halide-free conditions. Among the various amino acids and superbases systems tested, the L-histidine/1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU) system achieved the highest conversion of propylene oxide and selectivity of propylene carbonate. The effect of various reaction parameters was evaluated. A possible catalyst mechanism for L-histidine synergized with DBU in the ring opening of epoxide and DBU introduced CO₂ activation. The process herein represents a green, simple, and cost-effective route for the chemical fixation of CO₂ into cyclic carbonates.     

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.     

Differences in Reactivity of Epoxides in the Copolymerisation with Carbon Dioxide by Zinc-Based Catalysts: Propylene Oxide versus Cyclohexene Oxide

The homogeneous dinuclear zinc catalyst going back to the work of Williams et al. is to date the most active catalyst for the copolymerisation of cyclohexene oxide and CO₂ at one atmosphere of carbon dioxide. However, this catalyst shows no copolymer formation in the copolymerisation reaction of propylene oxide and carbon dioxide, instead only cyclic carbonate is found. This behaviour is known for many zinc‐based catalysts, although the reasons are still unidentified. Within our studies, we focus on the parameters that are responsible for this typical behaviour. A deactivation of the catalyst due to a reaction with propylene oxide turns out to be negligible. Furthermore, the catalyst still shows poly(cyclohexene carbonate) formation in the presence of cyclic propylene carbonate, but the catalyst activity is dramatically reduced. In terpolymerisation reactions of CO₂ with different ratios of cyclohexene oxide to propylene oxide, no incorporation of propylene oxide can be detected, which can only be explained by a very fast back‐biting reaction. Kinetic investigations indicate a complex reaction network, which can be manifested by theoretical investigations. DFT calculations show that the ring strains of both epoxides are comparable and the kinetic barriers for the chain propagation even favour the poly(propylene carbonate) over the poly(cyclohexene carbonate) formation. Therefore, the crucial step in the copolymerisation of propylene oxide and carbon dioxide is the back‐biting reaction in the case of the studied zinc catalyst. The depolymerisation is several orders of magnitude faster for poly(propylene carbonate) than for poly(cyclohexene carbonate).     

CO2‐Sourced α‐Alkylidene Cyclic Carbonates: A Step Forward in the Quest for Functional Regioregular Poly(urethane)s and Poly(carbonate)s

Described is a robust platform for the synthesis of a large diversity of novel functional CO₂‐sourced polymers by exploiting the regiocontrolled ring‐opening of α‐alkylidene carbonates by various nucleophiles. The reactivity of α‐alkylidene carbonates is dictated by the exocyclic olefinic group. The polyaddition of CO₂‐sourced bis(α‐alkylidene carbonate)s (bis‐αCCs) with primary and secondary diamines provides novel regioregular functional poly(urethane)s. The reactivity of bis‐αCCs is also exploited for producing new poly(β‐oxo‐carbonate)s by organocatalyzed polyaddition with a diol. This synthesis platform provides new functional variants of world‐class leading polymer families (polyurethanes, polycarbonates) and valorizes CO₂ as a chemical feedstock.     

Tuning the Gate‐Opening Pressure in a Switching pcu Coordination Network,X‐pcu‐5‐Zn,by Pillar‐Ligand Substitution

Coordination networks that reversibly switch between closed and open phases are of topical interest since their stepped isotherms can offer higher working capacities for gas‐storage applications than the related rigid porous coordination networks. To be of practical utility, the pressures at which switching occurs, the gate‐opening and gate‐closing pressures, must lie between the storage and delivery pressures. Here we study the effect of linker substitution to fine‐tune gate‐opening and gate‐closing pressure. Specifically, three variants of a previously reported pcu ‐topology MOF, X‐pcu‐5‐Zn , have been prepared: X‐pcu‐6‐Zn , 6 =1,2‐bis(4‐pyridyl)ethane (bpe), X‐pcu‐7‐Zn , 7 =1,2‐bis(4‐pyridyl)acetylene (bpa), and X‐pcu‐8‐Zn , 8 =4,4′‐azopyridine (apy). Each exhibited switching isotherms but at different gate‐opening pressures. The N₂, CO₂, C₂H₂, and C₂H₄ adsorption isotherms consistently indicated that the most flexible dipyridyl organic linker, 6 , afforded lower gate‐opening and gate‐closing pressures. This simple design principle enables a rational control of the switching behavior in adsorbent materials.     

无溶剂条件下硒酚对末端环氧化合物的开环反应及其在1,3-噁唑烷-2-酮衍生物合成中的应用

Regioselective ring-opening reactions of 1,2-epoxides with ArSeH catalyzed by Ti（O^tPr）4 under solvent-free conditions were investigated. A variety of β-hydroxyselenides were obtained in excellent yields of 90%-97% and regioselectivities by a simple, atom economic and environment-friendly procedure. Several N-tosyl- 1,3-oxazolidin-2-ones were prepared starting from the corresponding 1,2-epoxides and ArSeH by a one-pot three-step procedure.     

Tuning the Gate‐Opening Pressure in a Switching pcu Coordination Network,X‐pcu‐5‐Zn,by Pillar‐Ligand Substitution

Coordination networks that reversibly switch between closed and open phases are of topical interest since their stepped isotherms can offer higher working capacities for gas‐storage applications than the related rigid porous coordination networks. To be of practical utility, the pressures at which switching occurs, the gate‐opening and gate‐closing pressures, must lie between the storage and delivery pressures. Here we study the effect of linker substitution to fine‐tune gate‐opening and gate‐closing pressure. Specifically, three variants of a previously reported pcu ‐topology MOF, X‐pcu‐5‐Zn , have been prepared: X‐pcu‐6‐Zn , 6 =1,2‐bis(4‐pyridyl)ethane (bpe), X‐pcu‐7‐Zn , 7 =1,2‐bis(4‐pyridyl)acetylene (bpa), and X‐pcu‐8‐Zn , 8 =4,4′‐azopyridine (apy). Each exhibited switching isotherms but at different gate‐opening pressures. The N₂, CO₂, C₂H₂, and C₂H₄ adsorption isotherms consistently indicated that the most flexible dipyridyl organic linker, 6 , afforded lower gate‐opening and gate‐closing pressures. This simple design principle enables a rational control of the switching behavior in adsorbent materials.     

Unexpected Macrocyclic Multinuclear Zinc and Nickel Complexes that Function as Multitasking Catalysts for CO2 Fixations

Unique self‐assembled macrocyclic multinuclear Zn^II and Ni^II complexes with binaphthyl‐bipyridyl ligands (L) were synthesized. X‐ray analysis revealed that these complexes consisted of an outer ring (Zn₃L₃ or Ni₃L₃) and an inner core (Zn₂ or Ni). In the Zn^II complex, the inner Zn₂ part rotated rapidly inside the outer ring in solution on an NMR timescale. These complexes exhibited dual catalytic activities for CO₂ fixations: synthesis of cyclic carbonates from epoxides and CO₂ and temperature‐switched N‐formylation/N‐methylation of amines with CO₂ and hydrosilane.     

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.     

Substrate‐Controlled Product Divergence: Conversion of CO2 into Heterocyclic Products

Substituted epoxy alcohols and amines allow substrate‐controlled conversion of CO₂ into a wide range of heterocyclic structures through different mechanistic manifolds. This new approach results in an unusual scope of CO₂‐derived products by initial activation of CO₂ through either the amine or alcohol unit, thus providing nucleophiles for intramolecular epoxy ring opening under mild reaction conditions. Control experiments support the crucial role of the amine/alcohol fragment in this process with the nucleophile‐assisted ring‐opening step following an S_Ni pathway, and a 5‐exo‐tet cyclization, thus leading to heterocyclic scaffolds.     

Trapping N2 and CO2 on the Sub‐Nano Scale in the Confined Internal Spaces of Open‐Cage C60 Derivatives: Isolation and Structural Characterization of the Host–Guest Complexes

An open‐cage C₆₀ tetraketone with a large opening was able to encapsulate N₂ and CO₂ molecules after its exposure to high pressures of N₂ and CO₂ gas. A subsequent selective reduction of one of the four carbonyl groups on the rim of the opening induced a contraction of the opening (→ 2 ) and trapped the guest molecules inside 2 . The thus‐obtained host–guest complexes N₂@ 2 and CO₂@ 2 could be isolated by recycling HPLC, and were found to be stable at room temperature. The molecular structures of N₂@ 2 and CO₂@ 2 were determined by single‐crystal X‐ray diffraction analyses, and revealed a short N?N triple bond for the encapsulated N₂, as well as an unsymmetric molecular structure for the encapsulated molecule of CO₂. The IR spectrum of CO₂@ 2 suggested that the rotation of the encapsulated molecule of CO₂ is partially restricted, which was supported by DFT calculations.     

A Porphyrin‐Based Porous rtl Metal–Organic Framework as an Efficient Catalyst for the Cycloaddition of CO2 to Epoxides

A porous rtl metal–organic framework (MOF) [Mn₅L(H₂O)₆?(DMA)₂]?5DMA?4C₂H₅OH ( 1? Mn) (H₁₀L=5,10,15,20‐tetra(4‐(3,5‐dicarboxylphenoxy)phenyl)porphyrin; DMA=N,N′‐dimethylacetamide) was synthesized by employing a new porphyrin‐based octacarboxylic acid ligand. 1? Mn exhibits high Mn^II density in the porous framework, providing it great Lewis‐acid heterogeneous catalytic capability for the cycloaddition of CO₂ with epoxides. Strikingly, 1? Mn features excellent catalytic activity to the cycloaddition of CO₂ to epoxides, with a remarkable initial turnover frequency 400 per mole of catalyst per hour at 20 atm. As‐synthesized 1? Mn also exhibits size selectivity to different epoxide substrates on account of their steric hindrance. The high catalytic activity, size selectivity, and stability toward the epoxides on catalytic cycloaddition of CO₂ make 1? Mn a promising heterogeneous catalyst for fixation and utilization of CO₂.     

Silica Chloride Nano Particle Catalyzed Ring Opening of Epoxides by Aromatic Amines

Silica chloride nano particle (nano SiO₂‐Cl), has been found to be heterogeneous catalyst for facile, simple and mild ring opening of epoxides with aromatic amines to afford β‐amino alcohols in dry CH₂Cl₂ at room temperature.     

Oxygen‐Triggered Switchable Polymerization for the One‐Pot Synthesis of CO2‐Based Block Copolymers from Monomer Mixtures

Switchable polymerization provides the opportunity to regulate polymer sequence and structure in a one‐pot process from mixtures of monomers. Herein we report the use of O₂ as an external stimulus to switch the polymerization mechanism from the radical polymerization of vinyl monomers mediated by (Salen)Co^III?R [Salen=N,N′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediamine; R=alkyl] to the ring‐opening copolymerization (ROCOP) of CO₂/epoxides. Critical to this process is unprecedented monooxygen insertion into the Co?C bond, as rationalized by DFT calculations, leading to the formation of (Salen)Co^III?O?R as an active species to initiate ROCOP. Diblock poly(vinyl acetate)‐b‐polycarbonate could be obtained by ROCOP of CO₂/epoxides with preactivation of (Salen)Co end‐capped poly(vinyl acetate). Furthermore, a poly(vinyl acetate)‐b‐poly(methyl acrylate)‐b‐polycarbonate triblock copolymer was successfully synthesized by a (Salen)cobalt‐mediated sequential polymerization with an O₂‐triggered switch in a one‐pot process.     

A DFT study on the insertion of CO2 into styrene oxide catalyzed by 1‐butyl‐3‐methyl‐Imidazolium bromide ionic liquid

Green systems able to capture or fix CO₂ are becoming more important specially to reduce environmental impacts. In this work, the mechanism of insertion of CO₂ into styrene oxide (STYO) both in the absence and presence of the catalyst 1‐butyl‐3‐methyl‐imidazolium bromide (BMIm Br) was investigated through calculations based on density functional theory in the ωB97X‐D level. Two different routes were considered and it was shown they are energetically available and compete against each other. For both routes, the rate‐determinant step is the ring opening of STYO resulting from the nucleophilic attack of the Br^? on the C atom from STYO and is associated mainly to the participation of the cation and the anion from the catalyst in the reaction. Reactive indices and noncovalent interaction analysis were used as a tool to investigate this reason. This work allowed a better comprehension of the underlying mechanism and the supplied data provide valuable support for the design of new more efficient ionic liquid catalyst. © 2015 Wiley Periodicals, Inc.     

Reductive Ring‐Opening Reaction of 2,3‐Epoxy‐1,4‐butanediones with SbCl3‐Bu4NI in the Presence of Na2S2O3·5H2O

1,4‐Disubstituted 2,3‐epoxy‐1,4‐butanediones were converted to 1,4‐disubstituted 2‐hydroxy‐1,4‐butanediones with SbCl₃‐Bu₄NI in the presence of Na₂S₂O₃ · 5H₂O. The ring opening of terminal epoxides can also be accomplished to afford the corresponding haloalcohol with SbCl₃ and tetrabutylammonium halides, Bu₄NX (X=Cl, Br, I) under the same reaction conditions.