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Cleaner synthesis of amines remains a key challenge in organic chemistry because of their prevalence in pharmaceuticals, agrochemicals and synthetic building blocks. Here, we report a different paradigm for chemoselective hydrogenation of nitro compounds to amines, under mild, aqueous conditions. The hydrogenase enzyme releases electrons from H 2 to a carbon black support which facilitates nitro-group reduction. For 30 nitroarenes we demonstrate full conversion (isolated yields 78 – 96%), with products including pharmaceuticals benzocaine, procainamide and mesalazine, and 4-aminophenol – precursor to paracetamol (acetaminophen). We also showcase gram-scale synthesis of procainamide with 90% isolated yield. We demonstrate potential for extension to aliphatic substrates. The catalyst is highly selective for reduction of the nitro group over other unsaturated bonds, tolerant to a wide range of functional groups, and exhibits excellent stability in reactions lasting up to 72 hours and full reusability over 5 cycles with a total turnover number over 1 million, indicating scope for direct translation to fine chemical manufacturing. The reduction of nitro-groups is a common synthetic route to amines, but biocatalytic strategies for such reactions are still being developed. In this study, the authors repurposed the hydrogenase enzyme by immobilisation on carbon black to yield a heterogeneous chemobiocatalyst for selective production of amines.

This thesis explores the activity of single atom metal catalysts on graphene-like support (SACs) and metal nitrides for the nitrogen reduction reaction (NRR). Furthermore, extensive analysis of HER activity and in-situ characterisation are carried out to derive a structure-activity relationship of SACs in the hydrogen evolution reaction (HER). To that end, a library of single atom transition metals on nitrogen-doped graphene (M-NGs) with comparable compositions is synthesised by a carbon backbone method. Their HER activity is assessed showing Ru-NG and Co-NG to be highly active. The data is correlated with the φ factor, a computationally suggested descriptor for electron density on the metal site constituting the first experimental substantiation of this design principle. Additionally it is found that HER activity on cobalt-containing SACs can be further tuned by changing the coordination environment of the metal via the inclusion of oxygen into the first coordination shell. In in-situ XANES and IR spectroelectrochemical thiocyanate poisoning experiments three distinct active sites are observed and it is suggested that distortion from the square planar Co-N₄ environment caused by axial oxygen ligands leads to decreased HER activity. In the second part of this thesis Co₃Mo₃N was identified as a potential electrocatalyst for the direct reduction of N₂ to N³- in molten chloride eutectics. Based on experimental evidence and previous literature reports, a Mars van Krevelen-type mechanism is suggested for the reaction in which Li⁺ ions facilitate the activation of dinitrogen, as well as enable participation of the lattice nitrogen of Co₃Mo₃N.