Chemistry related to the actives sites of the [Fe]- and [FeFe]-hydrogenases
Hydrogenases are an important group of enzymes found in a range of microorganisms. There are three phylogenetically distinct classes of hydrogenase all of which feature iron-containing complexes. The work contained in this thesis has two main focuses: the synthesis and characterization of novel mimics of the [Fe]-hydrogenase active site, and spectroscopic studies on the interaction of iron-sulfur clusters with CO and CN− relevant to the biosynthesis of the H-cluster of [FeFe]-hydrogenase. The mechanism by which the [Fe]-hydrogenase functions is not fully understood, and biomimetic models currently offer limited insight. This emphasises the need to explore the fundamental organometallic chemistry of biologically relevant mono-iron complexes. Here, novel ferracyclic complexes featuring abiological ligands were synthesised, extending an existing family of mimics. Examination of the spectroscopic and electrochemical properties of these systems demonstrated that none are redox active in a range relevant to the enzyme. The route by which microorganisms convert {4Fe4S} precursors into the {2Fe2S} assembly of the H-cluster of [FeFe]-hydrogenase is currently attracting significant scientific attention, in particular how the Fe(CO)(CN) moiety of the subsite is assembled. Here, the reaction of CO and CN− with synthetic iron-sulfur clusters was used to seek out chemical precedence for the generation of this motif. It is clearly shown that Fe4S4 clusters can be functionalised with CO and CN− groups. Crucially, whilst good spectroscopic evidence for a complex featuring moiety A Fe(CO)(CN) was obtained this was not the case for an independent cluster featuring only moiety B Fe(CO)2(CN). However, there is some evidence for the formation of a cluster bearing both groups simultaneously.
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