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Mechanism of the Cycloaddition of Carbon Dioxide and Epoxides Catalyzed by Cobalt‐Substituted 12‐Tungstenphosphate
Author(s) -
Chen Fawang,
Li Xiaofang,
Wang Bo,
Xu Tiegang,
Chen ShiLu,
Liu Peng,
Hu Changwen
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201201042
Subject(s) - cycloaddition , catalysis , chemistry , epoxide , cobalt , catalytic cycle , polyoxometalate , reaction mechanism , electron transfer , photochemistry , solvent , carbon dioxide , medicinal chemistry , organic chemistry
Co II ‐substituted α‐Keggin‐type 12‐tungstenphosphate [( n ‐ C 4 H 9 ) 4 N] 4 H[PW 11 Co(H 2 O)O 39 ]‐ (PW 11 Co) is synthesized and used as a single‐component, solvent‐free catalyst in the cycloaddition reaction of CO 2 and epoxides to form cyclic carbonates. The mechanism of the cycloaddition reaction is investigated using DFT calculations, which provides the first computational study of the catalytic cycle of polyoxometalate‐catalyzed CO 2 coupling reactions. The reaction occurs through a single‐electron transfer from the doublet Co II catalyst to the epoxide and forms a doublet Co III –carbon radical intermediate. Subsequent CO 2 addition forms the cyclic carbonate product. The existence of radical intermediates is supported by free‐radical termination experiments. Finally, it is exhilarating to observe that the calculated overall reaction barrier (30.5 kcal mol −1 ) is in good agreement with the real reaction rate (83 h −1 ) determined in the present experiments (at 150 °C).