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New Set of Multicomponent Crystals as Efficient Heterogeneous Catalysts for the Synthesis of Cyclic Carbonates

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posted on 2019-03-13, 00:00 authored by Arunangshu Kundu, Swagata Saikia, Manoj Majumder, Oindrila Sengupta, Biswajit Bhattacharya, Gobinda Chandra De, Sushobhan Ghosh
Three new multicomponent crystals 1a–1c of Zn­(II), Mn­(II), and Co­(II), respectively, were synthesized by the reaction of 2,6-bis­(hydroxymethyl)­pyridine, the respective metal salts, and sodium benzoate in a 1:1:2 ratio. One component of these multicomponent crystals 1a–1c is the dicationic 2,6-bis­(hydroxymethyl)­pyridine metal complex and the other component is the dianionic tetrabenzoate complex of the same metal. The complexes were fully characterized by single-crystal X-ray structure determination. The X-ray structure of these compounds 1a–1c reveals the formation of 1D supramolecular chain parallel to the crystallographic b axis via H-bonding interactions between the dicationic and dianionic parts of the respective compound. The Mn­(II) (1b) and Co­(II) (1c) complexes show antiferromagnetic coupling between the two associated metal centers via the H-bonding interaction pathway. All the three compounds 1a–1c were tested as heterogeneous catalytic systems for the successful conversion of epoxides to cyclic carbonates in solvent-free condition under approximately 10 bar of pressure of CO2 and temperature ranging between 60 and 80 °C along with tetrabutyl ammonium bromide acting as a cocatalyst. All the three compounds 1a–1c were found to have turnover number more than 1000 for the respective epoxides except for the conversion of cyclohexene oxide to cyclohexene carbonate.