TY - JOUR
T1 - Modeling the Mechanism of CO2/Cyclohexene Oxide Copolymerization Catalyzed by Chiral Zinc β-Diiminates
T2 - Factors Affecting Reactivity and Isotacticity
AU - Shao, Huiling
AU - Reddi, Yernaidu
AU - Cramer, Christopher J.
N1 - Publisher Copyright:
Copyright © 2020 American Chemical Society.
PY - 2020/8/7
Y1 - 2020/8/7
N2 - Copolymerization of CO2 and cyclohexene oxide (CHO) upcycles CO2 into the value-added, chemically recyclable, thermoplastic poly(cyclohexene carbonate) (PCHC). Using density functional theory, the Zn-catalyzed copolymerization mechanism has been characterized with a particular focus on the effects of chiral β-diiminate (BDI) ligands as they influence the reactivity and enantioselectivity in the epoxide ring-opening step, where the latter is required for isotacticity. Theory indicates that both mono-and binuclear forms of the catalyst are involved along the reaction path, with the turnover-limiting step being ring-opening of the epoxide mediated by a binuclear catalyst. Subsequent CO2 insertion is predicted to be kinetically facile and preferentially mediated by a mononuclear catalyst. The predicted preference for epoxide opening to give R,R-stereocenters in the copolymer when N-(4-(((1S,2S)-2-(benzyloxy)cyclohexyl)amino)-5,5,5-trifluoropent-3-en-2-ylidene)-2,6-dimethylaniline is used as the BDI ligand agrees with the experiment and is attributed to differential ligand distortions associated with key non-bonded interactions in the competing transition-state structures. Further analysis predicts that 2,6-dichloro and dibromo substitutions of the BDI ligand N-aryl group(s) should result in increased rates and enantioselectivities for copolymerization.
AB - Copolymerization of CO2 and cyclohexene oxide (CHO) upcycles CO2 into the value-added, chemically recyclable, thermoplastic poly(cyclohexene carbonate) (PCHC). Using density functional theory, the Zn-catalyzed copolymerization mechanism has been characterized with a particular focus on the effects of chiral β-diiminate (BDI) ligands as they influence the reactivity and enantioselectivity in the epoxide ring-opening step, where the latter is required for isotacticity. Theory indicates that both mono-and binuclear forms of the catalyst are involved along the reaction path, with the turnover-limiting step being ring-opening of the epoxide mediated by a binuclear catalyst. Subsequent CO2 insertion is predicted to be kinetically facile and preferentially mediated by a mononuclear catalyst. The predicted preference for epoxide opening to give R,R-stereocenters in the copolymer when N-(4-(((1S,2S)-2-(benzyloxy)cyclohexyl)amino)-5,5,5-trifluoropent-3-en-2-ylidene)-2,6-dimethylaniline is used as the BDI ligand agrees with the experiment and is attributed to differential ligand distortions associated with key non-bonded interactions in the competing transition-state structures. Further analysis predicts that 2,6-dichloro and dibromo substitutions of the BDI ligand N-aryl group(s) should result in increased rates and enantioselectivities for copolymerization.
KW - catalysis
KW - catalyst design
KW - epoxide/COcopolymerization
KW - ligand effects
KW - mechanistic investigation
KW - stereoselectivity
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U2 - 10.1021/acscatal.0c02299
DO - 10.1021/acscatal.0c02299
M3 - Article
AN - SCOPUS:85091178194
SN - 2155-5435
VL - 10
SP - 8870
EP - 8879
JO - ACS Catalysis
JF - ACS Catalysis
IS - 15
ER -