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Aluminum porphyrins with quaternary ammonium halides as catalysts for copolymerization of cyclohexene oxide and CO2: metal-ligand cooperative catalysis

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Title: Aluminum porphyrins with quaternary ammonium halides as catalysts for copolymerization of cyclohexene oxide and CO2: metal-ligand cooperative catalysis
Authors: Deng, Jingyuan Browse this author
Ratanasak, Manussada Browse this author
Sako, Yuma Browse this author
Tokuda, Hideki Browse this author
Maeda, Chihiro Browse this author
Hasegawa, Jun-ya Browse this author →KAKEN DB
Nozaki, Kyoko Browse this author
Ema, Tadashi Browse this author
Issue Date: 14-Jun-2020
Publisher: Royal Society of Chemistry
Journal Title: Chemical science
Volume: 11
Issue: 22
Start Page: 5669
End Page: 5675
Publisher DOI: 10.1039/d0sc01609h
Abstract: Bifunctional Al-III porphyrins with quaternary ammonium halides, 2-Cl and 2-Br, worked as excellent catalysts for the copolymerization of cyclohexene oxide (CHO) and CO2 at 120 degrees C. Turnover frequency (TOF) and turnover number (TON) reached 10 000 h(-1) and 55 000, respectively, and poly(cyclohexene carbonate) (PCHC) with molecular weight of up to 281 000 was obtained with a catalyst loading of 0.001 mol%. In contrast, bifunctional Mg-II and Zn-II counterparts, 3-Cl and 4-Cl, as well as a binary catalyst system, 1-Cl with bis(triphenylphosphine)iminium chloride (PPNCl), showed poor catalytic performances. Kinetic studies revealed that the reaction rate was first-order in [CHO] and [2-Br] and zero-order in [CO2], and the activation parameters were determined: Delta H double dagger = 12.4 kcal mol(-1), Delta S double dagger = -26.1 cal mol(-1) K-1, and Delta G double dagger = 21.6 kcal mol(-1) at 80 degrees C. Comparative DFT calculations on two model catalysts, Al-III complex 2' and Mg-II complex 3', allowed us to extract key factors in the catalytic behavior of the bifunctional Al-III catalyst. The high polymerization activity and carbonate-linkage selectivity originate from the cooperative actions of the metal center and the quaternary ammonium cation, both of which facilitate the epoxide-ring opening by the carbonate anion to form the carbonate linkage in the key transition state such as TS3b (Delta H double dagger = 13.3 kcal mol(-1), Delta S double dagger = -3.1 cal mol(-1) K-1, and Delta G double dagger = 14.4 kcal mol(-1) at 80 degrees C).
Rights: https://creativecommons.org/licenses/by-nc/3.0/
Type: article
URI: http://hdl.handle.net/2115/79034
Appears in Collections:触媒科学研究所 (Institute for Catalysis) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

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