Second coordination sphere effects in [FeFe]-Hydrogenase mimics

Iron–iron hydrogenase are fascinating metallo‐enzymes able to reversibly perform interconversion between protons and dihydrogen with high rates at low overpotentials. Nevertheless, activity and stability of synthetic analogues without the protein matrix are rarely comparable to the enzyme.
This thesis investigates second coordination sphere effects around synthetic hydrogenase models.
Chapter 2 discusses di‐iron complexes featuring several pyridyl proton‐relays on phosphine ligands. This work demonstrates that proton‐responsive ligands alone are sufficient to achieve high catalytic rates in di‐iron hydrogenase mimics, while the overpotentials remain high.
Chapter 3 presents a straightforward approach for the immobilization of benzene dithiolate di‐iron complexes onto conductive (nano)FTO electrodes.
Specifically, we envision supramolecular M₁₂L₂₄ Fujita‐type cages as a suitable platform to introduce a second coordination sphere around synthetic di‐iron models, emulating the protein environment. Chapter 4 introduces supramolecular M₁₂L₂₄ cages, however this chapter focuses on the preparation of cages featuring redox‐active probes, encapsulated by both supramolecular or covalent strategies, to enable the study of heterogeneous electron transfer processes.
Chapter 5 describes the preparation of a sterically‐demanding molecular electrolyte inhibiting access to the cage cavity. Voltammetric investigation of cages containing redox‐active probes employing this large‐sized electrolyte revealed that these self‐assembled cages bear similarities to macroscopic Faraday cages.
Chapter 6 presents general approaches to introduce a second coordination sphere environment around di‐iron hydrogenases models. We demonstrate for the first time that tuning the local environment around the encapsulated catalyst affords a significantly decreased overpotential, highlighting the importance of the second coordination sphere for catalytic performance.