Modelling proton relays in molybdenum-containing metalloenzymes

Haque, Farhana (2022) Modelling proton relays in molybdenum-containing metalloenzymes. Doctoral thesis, University of East Anglia.

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Molybdenum is found in the active site of a number of metalloenzymes. It is supported in these systems by one or more sulphide ligands. This combination allows access to a range of oxidation states in which catalysis can take place. Mimicking this intriguing chemistry in synthetic models offers the potential to develop new catalysts for important industrial processes.

In this thesis, we explore the possibility of developing molybdenum-based mimics of two important systems: Nitrogenase and Formate Dehydrogenase (FDH). Central to this modelling is the introduction of a proton relay. These are present in the native enzyme but are largely absent in the currently known synthetic models. Two approaches were explored in developing nitrogenase mimics. We first utilised a range of N -heterocyclic carbenes around molybdenum centre to enhance its electron density. Regrettably we were unable to isolate the target systems. Our second approach was to have molybdenum complexes supported by PNP ligands. Novel PNP ligands were synthesised and coordinated to molybdenum. Crystallisation showed that these ligands gave a mixture of mono- and bis(PNP) complexes. This precluded the study of the reactivity of the individual systems.

Shifting our attention to FDH models, we first developed a new synthetic route to functionalised molybdenum bis dithiolenes. The overall synthetic strategy utilised a 1,3-dithiolone as the key intermediate. Our ligand included a pendant hydroxy group for proton relay. Our initial aim was to explore the effect of a range of protecting groups on the oxygen of the hydroxy group by deprotecting the ligand once it was coordinated to molybdenum. Unfortunately, the deprotection step was too harsh for our molybdenum carbonyl complex and it decomposed within minutes. We then switchedsw to using the well established technique of transmetallation via nickel. Whilst this impacted on yield, this allowed us to access the target complexes.

Computational simulation is a powerful method for studying difficult to access systems. Here, we employed Density Functional Theory (DFT) to model the behaviour of our target complexes. We established that there is not one strongly preferred isomer.

Electrochemical methods are central to understanding the catalysis of redox active metals. We have studied the fundamental electrochemistry of our nickel and molybdenum dithiolenes and found them to be comparable to literature complexes. We explored the ability of our novel molybdenum dithiolene to catalyse electroreduction, revealing two competing pathways.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Chemistry
Depositing User: Chris White
Date Deposited: 18 Jan 2023 11:34
Last Modified: 18 Jan 2023 11:34


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