Versatility of Boron-Mediated Coupling Reaction of Oxetanes and Epoxides with CO2: Selective Synthesis of Cyclic Carbonates or Linear Polycarbonates

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Zhang, Cheng Jian
Wu, Shao Qi
Boopathi, Senthil
Zhang, Xing Hong
Hong, Xin
Gnanou, Yves
Feng, Xiaoshuang

KAUST Department
Academic Affairs
Chemical Science Program
Office of the VP
Physical Science and Engineering (PSE) Division

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Achieving simultaneously high selectivity and high rate in the coupling reaction of CO2 with poorly reacting oxetanes remains a major challenge. Here, the selective and nearly quantitative conversion of the coupling reaction of oxetanes with CO2 into six-membered cyclic organic carbonates (COCs) is described, when a binary metal-free system composed of commercially available alkyl borane and onium iodide salts is used under 10 bar CO2 pressure between 90 and 110 °C. Kinetic investigations provide quantitatively the enthalpy and entropy of activation [ΔH‡ = 6.7 ± 1.2 kcal/mol and ΔS‡ = -57 ± 4 cal/(mol·K)] of the back-biting, cyclic formation reaction. In addition to forming borate complexes with the anions responsible for the CO2/oxetane coupling reaction, these alkyl boranes activate the cyclic ethers as unambiguously confirmed by density functional theory studies. Upon selecting onium salts other than iodide-based ones, in particular those with poor leaving ability, the process is driven toward chain growth and the formation of linear polycarbonates. This metal-free system also exhibits both versatility and an activity comparable to that of metal catalysts (turnover frequency values of 14-124 h-1) for the synthesis of various five-membered COCs from epoxides and CO2.

Zhang, C.-J., Wu, S.-Q., Boopathi, S., Zhang, X.-H., Hong, X., Gnanou, Y., & Feng, X.-S. (2020). Versatility of Boron-Mediated Coupling Reaction of Oxetanes and Epoxides with CO2: Selective Synthesis of Cyclic Carbonates or Linear Polycarbonates. ACS Sustainable Chemistry & Engineering, 8(34), 13056–13063. doi:10.1021/acssuschemeng.0c04768

X.-H.Z. gratefully acknowledges financial support of the National Science Foundation of People’s Republic of China (nos. 51973190 and 21774108). X.H. is grateful for financial support from the National Natural Science Foundation of China (21702182, 21873081) and the Fundamental Research Funds for the Central Universities (2-2050205-19-361). C.-J.Z. acknowledges support of KAUST for his stay in Gnanou’s laboratory

American Chemical Society (ACS)

ACS Sustainable Chemistry & Engineering


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