Controlling self-assembly of zinc(II)-benzoate coordination complexes with 1,4-bis(4-pyridyl)ethane by varying solvent and ligand-to-metal ratio: Their catalytic activities

Four new coordination polymers formed by zinc-benzoate with the 1,2-bis(4-pyridyl)ethane (bpe) bridging ligand have been prepared and characterized. Zinc-benzoates can be rationally tuned to form four different structures with a bridging bpe ligand by controlling ligand-to-zinc-benzoate molar ratios and by using different solvent systems, and reveal three coordination polymers having similar one-dimensional characteristics but having different mono-, di-, trinuclear nodes (1-3), and a dinuclear ring type molecule (4). This work reveals that the ligand-to-metal ratio and solvent play very important roles in the formation of different coordination structures. We have also shown that the compounds 1-4 catalyzed efficiently the transesterification of a variety of esters. The complex 3 showed the most efficient reactivity and is the best among the catalytic efficiencies reported previously with zinc-containing coordination and polymeric compounds. The substrates with the electron-withdrawing substituents have undergone faster transesterification than those with the electron-donating ones. In addition, the scope of the application of 1-4 as transesterification catalysts has been expanded to now include ethanol and propanol, suggesting that this catalytic system can be potentially useful for preparing various esters by transesterification. Moreover, the transesterification reaction mechanism was discussed by ¹H NMR study.