[FeFe]hydrogenase mimics for proton reduction catalysis: Supramolecular proton reduction catalysts with appended redox-active and proton-responsive ligands towards application in a molecular artificial leaf

Hydrogen gas is a viable, sustainable alternative to fossil fuels, but only when produced from sustainable resources such as water and sunlight. Devices that can perform the photocatalytic splitting of water are colloquially called ‘artificial leaves’ and should contain at least a light-absorbing entity and water splitting catalysts. In this thesis, molecular catalysts are studied that mimic the all-iron hydrogenase enzyme which can convert electrons and protons into dihydrogen. Two main functionalities are crucial to the efficient operation of the enzyme: a proton relay and an electron reservoir to pre-organize the reaction substrates close to the active site. Chapter 3 elaborates on a catalyst that incorporates such a proton relay in the form of a phosphoramidite ligand which speeds up the overall catalytic reaction rate. Chapters 4 and 5 are devoted to mimics coupled to phosphole ligands that act akin the electron reservoir present in the enzyme. The inclusion of this latter functionality leads to a synthetic electrocatalyst that is on a par with the natural enzyme, operating at high rates in aqueous environment and being tolerant to oxygen. All these catalysts can be coupled, in a supramolecular fashion, to porphyrin photosensitizers which are based on the chlorophyll units present in the natural photosystems. Chapter 6 presents porphyrinic metal-organic frameworks grown onto electrodes which can accommodate supramolecular catalysts to, as a whole, form part of an artificial leaf.