Highly Active and Robust Metalloporphyrin Catalysts for the Synthesis of Cyclic Carbonates from a Broad Range of Epoxides and Carbon Dioxide

Bifunctional metalloporphyrins with quaternary ammonium bromides (nucleophiles) at the meta, para, or ortho positions of meso‐phenyl groups were synthesized as catalysts for the formation of cyclic carbonates from epoxides and carbon dioxide under solvent‐free conditions. The meta‐substituted catalysts exhibited high catalytic performance, whereas the para‐ and ortho‐substituted catalysts showed moderate and low activity, respectively. DFT calculations revealed the origin of the advantage of the meta‐substituted catalyst, which could use the flexible quaternary ammonium cation at the meta position to stabilize various anionic species generated during catalysis. A zinc(II) porphyrin with eight nucleophiles at the meta positions showed very high catalytic activity (turnover number (TON)=240 000 at 120 °C, turnover frequency (TOF)=31 500 h^?1 at 170 °C) at an initial CO₂ pressure of 1.7 MPa; catalyzed the reaction even at atmospheric CO₂ pressure (balloon) at ambient temperature (20 °C); and was applicable to a broad range of substrates, including terminal and internal epoxides.     

Azo-Functionalized Zirconium-Based Metal−Organic Polyhedron as an Efficient Catalyst for CO2 Fixation with Epoxides

Chemical fixation of CO₂ as C1 source at ambient temperature and low pressure is an energy-saving way to make use of the green-house gas, but it still remains a challenge since efficient catalyst with high catalytic active sites is required. Here, a novel monoclinic azo-functionalized Zr-based metal−organic polyhedron (Zr-AZDA) has been prepared and applied in CO₂ fixation with epoxides. The inherent azo groups not only endow Zr-AZDA with good solubilization, but also act as basic sites to enrich CO₂ showing efficient synergistic catalysis as confirmed by TPD-CO₂ analysis. XPS results demonstrate that the Zr active sites in Zr-AZDA possess suitable Lewis acidity, which satisfies both substrates activation and products desorption. DFT calculation indicates the energy barrier of the rate-determining step in CO₂ cycloaddition could be reduced remarkably (by ca. 60.9 %) in the presence of Zr-AZDA, which may rationalize the mild and efficient reaction condition employed (80 °C and 1 atm of CO₂). The work provides an effective multi-functional cooperative method for improvement of CO₂ cycloaddition.     

超临界二氧化碳中组氨酸催化合成环状碳酸酯

研究了超临界二氧化碳中α-氨基酸催化二氧化碳与环氧化物环加成反应合成环状碳酸酯,发现组氨酸的催化活性最高.在二氧化碳压力为8MPa、反应温度130℃、反应时间48h、组氨酸加入量为0.8mol%的条件下,二氧化物可以顺利的与各种环氧化物反应,以高的选择性和产率生成相应的环状碳酸酯.     

Synthesis of Cyclic Carbonates Catalysed by Aluminium Heteroscorpionate Complexes

New aluminium scorpionate based complexes have been prepared and used for the synthesis of cyclic carbonates from epoxides and carbon dioxide. Bimetallic aluminium(heteroscorpionate) complexes 9 – 14 were synthesised in very high yields. The single‐crystal X‐ray structures of 12 and 13 confirm an asymmetric κ²‐NO‐μ‐O arrangement in a dinuclear molecular disposition. These bimetallic aluminium complexes were investigated as catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide in the presence of ammonium salts. Under the optimal reaction conditions, complex 9 in combination with tetrabutylammonium bromide acts as a very efficient catalyst system for the conversion of both monosubstituted and internal epoxides into the corresponding cyclic carbonates showing broad substrate scope. Complex 9 and tetrabutylammonium bromide is the second most efficient aluminium‐based catalyst system for the reaction of internal epoxides with carbon dioxide. A kinetic study has been carried out and showed that the reactions were first order in complex 9 and tetrabutylammonium bromide concentrations. Based on the kinetic study, a catalytic cycle is proposed.     

Cyclic carbonate synthesis from epoxides and CO2 over cyanocobalamin/n‐Bu4NI

The synthesis of cyclic carbonates from epoxides and carbon dioxide catalyzed by cyanocobalamin and n‐Bu₄NI system was achieved under 0.8 MPa CO₂ pressure at 140°C without organic solvents. Propylene carbonate was obtained in 99% yield within 6 h under the optimized reaction conditions. The cyanocobalamin catalyst could be recycled with water and retained moderate catalytic activity. Copyright © 2012 John Wiley & Sons, Ltd.     

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.     

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.