Synthesis and electrochemical properties of [FeFe]-hydrogenase model complexes with acid-functionalized or base-functionalized ligands

Abstract

In the presence of Me3NO in THF solution, the treatment of a diiron model complex (μ-dmedt)Fe2(CO)6 (dmedt = 2,3-butanedithiol) with carboxylic acid-functionalized (3-carboxypyridine) and amino-functionalized (4-aminopyridine) ligands afforded two new diiron model complexes, (μ-dmedt)Fe2(CO)5(3-COOHPy) (2) and (μ-dmedt)Fe2(CO)5(4-NH2Py) (3). Research on the influence of the 3-COOHPy and 4-NH2Py ligands upon the electrocatalytic characteristics of the diiron dithiolate core have been discussed in terms of spectroscopic and electrochemical findings. In the presence of HOAc in CH3CN solution, electrochemical studies show that complexes 2 and 3 can catalyse hydrogen evolution, with TOFs (the turnover frequencies) of 174.09 and 74.88 mol H2 (mol·cat)−1 h−1 cm−2 for complexes 2 and 3 at −1.96 V versus Fc+/Fc, respectively. The hydrogen evolution overpotentials of complexes 2 and 3 in the presence of HOAc in CH3CN solution were 0.73 and 0.82 V, respectively. Comparatively, complex 2 produces hydrogen at an overpotential 90 mV lower than complex 3 does. Complex 2 also has a better ability for electrocatalytic H2 production than complex 3. These studies provide a basic perception of the stereo-electronic characteristics related to the design for effective hydrogenase model complexes. Two new diiron model complexes, (μ-dmedt)Fe2(CO)5(3-COOHPy) (2), (μ-dmedt)Fe2(CO)5(4-NH2Py) (3), have been prepared, which served as efficient molecular electrocatalysts in the CH3CN solution, and the electrochemical studies show that complexes 2 and 3 can catalyse hydrogen evolution with TOFs of 174.09 and 74.88 mol H2 (mol·cat)−1 h−1 cm−2 for complexes 2 and 3 at −1.96 V versus Fc/Fc+, respectively.