29443-23-0Relevant articles and documents
Scalable Bifunctional Organoboron Catalysts for Copolymerization of CO2and Epoxides with Unprecedented Efficiency
Yang, Guan-Wen,Zhang, Yao-Yao,Xie, Rui,Wu, Guang-Peng
, p. 12245 - 12255 (2020)
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 >99percent 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.
Dynamic Covalent Chemistry of Nucleophilic Substitution Component Exchange of Quaternary Ammonium Salts
Kulchat, Sirinan,Lehn, Jean-Marie
, p. 2484 - 2496 (2015/11/02)
Dynamic covalent libraries (DCLs) of quaternary ammonium cations were set up by reversible nucleophilic substitution (SN2′ and SN2) exchange reactions of ammonium salts and tertiary amines. The reactions were conducted at 60 °C to generate thermodynamically and kinetically controlled mixtures of quaternary ammonium compounds and tertiary amines, and were accelerated by using iodide as a nucleophilic catalyst. Microwave irradiation was used to assist the exchange reaction between the pyridinium salts and pyridine derivatives. Finally, experiments towards the generation of dynamic ionic liquids were performed. The results of this study pave the way for the extension of dynamic combinatorial chemistry to nucleophilic substitution reactions.
Equilibrium Studies of α-Diimine Displacement in Cationic Allylpalladium(II) Complexes by Monodentate N-Donors and the Mechanism of Allyl Amination by Triethylamine and Pyridine
Canovese, Luciano,Visentin, Fabiano,Uguagliati, Paolo,Bianca, Francesca Di,Antonaroli, Simonetta,Crociani, Bruno
, p. 3113 - 3118 (2007/10/02)
In the cationic complexes 3-allyl)(L-L)>ClO4 the chelated α-diimine was rapidly and reversibly displaced by secondary amines (N-methylaniline, morpholine or piperidine), triethylamine and 4-substituted pyridines.The observed equilibrium constants Ke increased with increasing basicity and decreasing steric requirements of the entering N-donor.They strongly depend on the α-diimine and decrease in the order RN=CHCH=NR RN=C(Me)C(Me)=NR ca.NC5H4(CH=NR)-2 (R = C6H4OMe-4).The cationic complex 3-C3H5)>(1+) underwent a slow allyl amination by triethylamine or pyridine (L') in the presence of fumaronitrile (fn), yielding 2-fn)> and Et3N(1+)CH2CH=CH2 or C5H5N(1+)CH2CH=CH2.Kinetic studies showed that the pseudo-first order rate constants for amination (kobs) are given by kobs = k2, suggesting a direct bimolecular attack of L' on the η3-allyl ligand.Amination hardly proceeds in the presence of the less-activated olefin dimethyl fumarate (dmf).The ?-accepting properties of the olefinic ligands play an important role also in the reaction of Et3N(1+)CH2CH=CH2 or C5H5N(1+)CH2CH=CH2 with 2-olefin)> (olefin = fn or dmf), i.e. the reverse of the amination reaction.
