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

摘要

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 bromideacting as a cocatalyst. All the three compounds >1a–1c were found to have turnover number more than 1000 for the respectiveepoxides except for the conversion of cyclohexene oxide to cyclohexenecarbonate.