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

Three new multicomponent crystals 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 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 reveals the formation of 1D supramolecular chain parallel to the crystallographic axis via H-bonding interactions between the dicationic and dianionic parts of the respective compound. The Mn(II) () and Co(II) () complexes show antiferromagnetic coupling between the two associated metal centers via the H-bonding interaction pathway. All the three compounds 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 CO and temperature ranging between 60 and 80 °C along with tetrabutyl ammonium bromide acting as a cocatalyst. All the three compounds were found to have turnover number more than 1000 for the respective epoxides except for the conversion of cyclohexene oxide to cyclohexene carbonate.