Electrocatalytic hydrogen production with [FeFe]-hydrogenase mimics by tetracene derivatives

The synthesis, structure, physical property, and electrocatalytic hydrogen production of tetrathia-tetracene ligand based [FeFe]-hydrogenase mimic molecules were investigated. By adjusting the amount of iron, mono- and bis-[FeFe] coordinated complexes 1 and 2 were synthesized. The structures of 1 and 2 were analysed by NMR, IR, absorption spectra, cyclic voltammogram, and DFT computation analyses. In DFT electron density maps, the HOMOs and LUMOs were located at tetrathia-tetracene units, indicated that these complexes remain mainly acene characteristics. When weak acid of Et3NHBF4 was added to the CH2Cl2 solutions of 1 or 2, the reductive potential of iron complexes was shifted to more positive values proportional to the concentration of acid. As the acid concentration increased, the current of reductive wave also increased, indicating the occurrence of catalytic proton reduction reaction. The bulk electrolysis reaction showed 65.8 TON for 1, and 52.8 TON for 2.