Computational Studies Into Factors That Influence the Structure and Reactivity of Nitrogenase's Biomimetic Transition Metal Complexes

Abstract

Many important large scale industrial reactions are performed using unsustainable or otherwise energy inefficient processes requiring high temperatures and pressures. In nature, enzymes are capable of catalysing a number of such reactions under ambient conditions. Through the understanding of how the enzymes achieve their catalytic activity, synthetic analogues capable of mimicking some of their properties can be created. With sufficient development, one day such catalysts may be employed on a large scale to allow these reactions to be carried out at ambient (or at least milder) conditions. The reactions which are discussed in this thesis are N2 --> NH3 and CO --> CnHm, both of which are known to be catalysed by the nitrogenase enzymes. The former reaction is undertaken industrially using the Haber-Bosch process, with ammonia being an important product used for various applications, perhaps the most notable being the nitrogen source in fertiliser. The latter reaction is done using the Fischer-Tropsch process, with the product hydrocarbons otherwise typically obtained from unsustainable reserves. The computational work presented in this thesis, using DFT, aims to further the understanding of the functionality of synthetic complexes displaying catalytic activity of relevance to these reactions, and relate it to the functionality of the nitrogenase enzymes where possible. Chapters 3 and 4 investigate the [MFe3S4] 3+ cubane complexes, where M is Mo/V, in relation to the binding and reduction of hydrazine (Chapter 3) and carbon monoxide (Chapter 4). The electronic structure features enabling catalytic activity and possible mechanistic pathways are presented. Furthermore, connections to the enzyme systems are made by comparing and contrasting the results between the Mo and V complexes. Chapter 5 investigates the reduction of N2 by a mononuclear Fe complex through the formation of a mu-binding [Fe-N-N-Fe] species. The electronic structure features enabling catalytic activity are discussed and the likely protonation order of N2 is proposed.

Date of Award	1 Aug 2025
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Michael Anderson (Supervisor), Patrick O'Malley (Supervisor) & Samuel De Visser (Supervisor)