Synthesis and characterization of photocatalytically active [FeFe]-hydrogenase subsite models
Silicon containing [FeFe] hydrogenase model complexes show interesting properties as sulfur protonation due to an increased basicity by o(Si-C)-3p(S) filled-filled interaction, reduced overpotential for proton reduction and the formation of a the rotated state under reductive conditions. With these model complexes the generation of H2 was only possible within electrocatalysis. In the present thesis a new approach was established with feasible synthetic pathways towards small and compact photocatalytic active [FeFe] hydrogenase model complexes with silicon containing heteroaromatic systems as the photosensitizer as well as one carbon analogue system directly imbedded into the bridging dithiolate unit. The synthesized model complexes as well as all other compounds were fully characterized by NMR and IR spectroscopy, mass spectrometry, elemental analysis, UV-vis and fluorescence spectroscopy, XRD analysis as well as cyclovoltammetry. Further theoretical studies were performed for a better understanding of these systems. Finally, comprehensive photocatalytic investigations were carried out. Within this work a turn-over number of 539 were reached under optimized conditions after 7 h irradiation, what represents an exceptionally turn-over frequency of 77 molecules H2/h. The approach of creating such small and compact [FeFe] hydrogenase model complexes makes this design to a powerful platform for proton reduction catalysts. A different aspect of this work was the utilization of the sterically bulky and silicon containing dithiolate as linker in a [FeFe] hydrogenase model compound for the investigation of the rotated state species of [FeIFeI] subsite models. Inspired by recently published results is reported an example with the highest degree of rotation so far (87,1°) for [FeIFeI] hydrogenase models without any agostic interactions (Fe…H-C).
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