Silicon-Heteroaromatic [FeFe] hydrogenase model complexes: insight into protonation, electrochemical properties, and molecular structures.

To learn from Nature how to create an efficient hydrogen-producing catalyst, much attention has been paid to the investigation of structural and functional biomimics of the active site of [FeFe]-hydrogenase. To understand their catalytic activities, the mu-S atoms of the dithiolate bridge have been considered as possible basic sites during the catalytic processes. For this reason, a series of [FeFe]-H(2)ase mimics have been synthesized and characterized. Different [FeFe]-hydrogenase model complexes containing bulky Si-heteroaromatic systems or fluorene directly attached to the dithiolate moiety as well as their mono-PPh3-substituted derivatives have been prepared and investigated in detail by spectroscopic, electrochemical, X-ray diffraction, and computational methods. The assembly of the herein reported series of complexes shows that the mu-S atoms can be a favored basic site in the catalytic process. Small changes in the (hetero)-aromatic system of the dithiolate moiety are responsible for large differences in their structures. This was elucidated in detail by DFT calculations, which were consistent with the experimental results.