The metallic catalyst-dominated alternating copolymerization of CO2 and epoxides has flourished for 50 years; however, the involved multistep preparation of the catalysts and the necessity to remove the colored metal residue in the final product present significant challenges in scalability. Herein, we report a series of highly active metal-free catalysts featured with an electrophilic boron center and a nucleophilic quaternary ammonium halide in one molecule for copolymerization of epoxides and CO2. The organocatalysts are easily scaled up to kilogram scale with nearly quantitative yield via two steps using commercially available stocks. The organocatalyst-mediated copolymerization of cyclohexane oxide and CO2 displays high activity (turnover frequency up to 4900 h–1) and >99% polycarbonate selectivity in a broad temperature range (25–150 °C) at mild CO2 pressure (15 bar). At a feed ratio of cyclohexane oxide/catalyst = 20 000/1, an efficiency of 5.0 kg of product/g of catalyst was achieved, which is the highest record achieved to date. The unprecedented activity toward CO2/epoxide copolymerization for our catalyst is a consequence of an intramolecular synergistic effect between the electrophilic boron center and the quaternary ammonium salt, which was experimentally ascertained by reaction kinetics studies, multiple control experiments, 11B NMR investigation, and the crystal structure of the catalyst. Density functional theory calculations further corroborated experimental conclusions and provided a deeper understanding of the catalysis process. The metal-free characteristic, scalable preparation, outstanding catalytic performances along with long-term thermostability demonstrate that the catalyst could be a promising candidate for large-scale production of CO2-based polymer.

Citrus essential oils (CEOs) are a mixture of volatile compounds consisting mainly of monoterpene hydrocarbons and are widely used in the food and pharmaceutical industries because of their antifungal activities. To face the challenge of growing public awareness and concern about food and health safety, studies concerning natural biopreservatives have become the focus of multidisciplinary research efforts. In the past decades, a large amount of literature has been published on the antifungal activity of CEOs. This paper reviews the advances of research on CEOs and focuses on their in vitro and food antifungal activities, chemical compositions of CEOs, and the methods used in antifungal assessment. Furthermore, the antifungal bioactive components in CEOs and their potential mechanism of action are summarized. Finally, the applications of CEOs in the food industry are discussed in an attempt to provide new information for future utilization of CEOs in modern industries.

The copolymerization of carbon dioxide (CO 2 ) and epoxides to produce aliphatic polycarbonates is a burgeoning technology for the large-scale utilization of CO 2 and degradable polymeric materials. Even with the wealth of advancements achieved over the past 50 years on this green technology, many challenges remain, including the use of metal-containing catalysts for polymerization, the removal of the chromatic metal residue after polymerization, and the limited practicable epoxides, especially for those containing electron-withdrawing groups. Herein, we provide kinds of pinwheel-shaped tetranuclear organoboron catalysts for epichlorohydrin/CO 2 copolymerization with >99% polymer selectivity and quantitative CO 2 uptake (>99% carbonate linkages) under mild conditions (25−40 °C, 25 bar of CO 2 ). The produced poly(chloropropylene carbonate) has the highest molecular weight of 36.5 kg/mol and glass transition temperature of 45.4 °C reported to date. The energy difference (ΔE a = 60.7 kJ/mol) between the cyclic carbonate and polycarbonate sheds light on the robust performance of our metal-free catalyst. Control experiments and density functional theory (DFT) calculations revealed a cyclically sequential copolymerization mechanism. The metal-free feature, high catalytic performance under mild conditions, and no trouble with chromaticity for the produced polymers imply that our catalysts are practical candidates to advance the CO 2 -based polycarbonates.

This manuscript describes a kind of bifunctional organocatalyst with unprecedented reactivity for the synthesis of polyethers via ring‐opening polymerization (ROP) of epoxides under mild conditions. The bifunctional catalyst incorporates two 9‐borabicyclo[3.3.1]nonane centers on the two ends as Lewis acidic sites for epoxide activation and a quaternary ammonium halide in the middle as the initiating site. The catalyst could be easily prepared in two steps from commercially available stocks on up to kilogram scale with ≈100 % yield. The organoboron catalyst mediated ROP of epoxides displays living behavior with low catalyst loading (5 ppm) and enables the synthesis of polyethers with molecular weights of over a million grams per mole (>106 g mol−1). Based on the investigations on crystal structure of catalyst, MALDI‐TOF, and 11B NMR spectroscopy, an intramolecular ammonium cation assisted SN2 mechanism is proposed and verified by DFT calculations.

Producing polyesters with high molecular weight (Mn) through ring‐opening copolymerization (ROCOP) of epoxides with cyclic anhydrides remains a major challenge. Herein, we communicate a metal‐free, highly active, and high thermoresistance system for the ROCOP of epoxides with cyclic anhydrides to prepare polyesters (13 examples). The organoboron catalysts can endure a reaction temperature as high as 180 °C for the ROCOP of cyclohexane oxide (CHO) with phthalic anhydride (PA) without the observation of any side reactions. The average Mn of the produced poly(CHO‐alt‐PA) climbed to 94.5 kDa with low polydispersity (Ð=1.19). Furthermore, an unprecedented turnover number of 9900, equivalent to an efficiency of 7.4 kg of polyester/g of catalyst, was achieved at a feed ratio of CHO/PA/catalyst=20000:10000:1 at 150 °C. Kinetic studies, crystal structure analysis, 11B NMR spectra, and DFT calculations provided mechanistic justification for the effectiveness of the catalyst system.

As eries of highly active organoboron catalysts for the coupling of CO 2 and epoxides with the advantages of scalable preparation, thermostability,a nd recyclability is reported. The metal-free catalysts show high reactivity towards aw ide scope of cyclic carbonates (14 examples) and can withstand ahigh temperature up to 150 8 8C. Compared with the current metal-free catalytic systems that use mol %c atalyst loading, the catalytic capacity of the catalyst described herein can be enhanced by three orders of magnitude (epoxide/cat. = 200 000/1, mole ratio) in the presence of ac ocatalyst. This feature greatly narrows the gap between metal-free catalysts and state-of-the-art metallic systems.A ni ntramolecular cooperative mechanism is proposed and certified on the basis of investigations on crystal structures,s tructure-performance relationships,k inetic studies,a nd key reaction intermediates. Scheme 1. The coupling reaction of CO 2 and epoxide.

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The dynamic Lewis multicore system (DLMCS) which integrates the Lewis acidic boron center(s) and an ammonium salt in one molecule has shown good catalytic performance in polymer synthesis. Inspired by the insightful intramolecular ammonium cation assisted mechanism, herein, we communicated a superior organoboron system by replacing a nitrogen atom with a phosphorus atom. The upgraded mono-, di-, and trinuclear organoboron catalysts show significantly improved catalytic performance and heat resistance for versatile epoxideinvolved transformations, including ring-opening copolymerization of epoxides and cyclic anhydrides, copolymerization of CO 2 and epoxides, and ring-opening polymerization of epoxides. 11 B NMR, single-crystal X-ray diffraction, and DFT results imply that the replacing nitrogen with phosphorus in an onium cation led to an effective epoxide activation and nucleophilic attack of the counterion on the activated epoxide, which remarkably shortened the initiation period and accelerated chain expansion, resulting in the obvious improvement of the activity. The upgraded phosphonium-containing organoboron system combined with the mechanism study and insightful understanding would be instructive in designing advanced metal-free catalysts.