Ghosh, S; (2015) Enzyme inspired proton reduction catalysts. Doctoral thesis , UCL (University College London).

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Abstract

This thesis demonstrates electrocatalytic proton reduction by a variety of molecular catalysts including biomimetic models of [FeFe]-hydrogenase enzyme. Hydrogenases are group of metalloenzymes capable of reversible reduction of protons into dihydrogen and are divided into three groups according to the metal content in their active sites namely [FeFe]-hydrogenase, [NiFe]-hydrogenase and [Fe]-hydrogenase. The principle objective of this work has been the development of efficient iron-based electrocatalysts that can catalyse the reduction of protons at reasonably mild potentials. Chapter 1 provides an overview of electrocatalytic proton reduction by earthabundant metal complexes together with a brief discussion of hydrogenase enzymes and model complexes developed to mimic the function of the [FeFe]- hydrogenase. The synthesis, characterisation and catalytic properties of diiron biomimetics containing various diamines and diphosphines are detailed in Chapters 2-5. Most of these ligands are electrochemically non-innocent and were used in order to mimic the function of the [FeFe]-hydrogenase active site as the later also bonded to an additional redox co-factor which relays electron to-from the diiron centre during catalysis. Chapters 6-7 detail the synthesis, structure and electrocatalytic proton reduction ability of octahedral and square-pyramidal mononuclear iron complexes. These complexes have certain features of the active site of [FeFe]-hydrogenase and are shown to be efficient catalysts for the reduction of protons. Chapters 8-10 detail electrocatalytic proton reduction by low-valent iron carbonyl clusters. All have an electronegative main group element directly bonded to the cluster core which provides a site for acidic hydrogen to interact with metalbound basic hydride during catalysis. Electrocatalytic proton reduction by related triruthenium 2-aminopyridinate clusters has also been described in Chapter 10.

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