Iron imide chemistry

Lee, S.C. (2002) Iron-imide clusters and nitrogenase Abiological chemistry of biological relevance In Leigh, G. J. and Winterton, N. (eds) Modem Coordination Chemistry Royal Society of Chemistry, Cambridge, pp. 278-287. 

Iron-Imide Clusters and Nitrogenase A biological Chemistry of Biological Relevance ... 

Iron-Imide Clusters and Nitrogenase Abiological Chemistry of Biological Relevancel... 

The synthesis of the imidoiron cubane 4 and the possibility of cluster-bound imide ligands as intermediates during nitrogenase turnover has led us to a general exploration of weak-field iron-imide (Fe-NR) cluster chemistry. Our initial studies establish the existence of a rich reaction manifold that is readily accessible from simple iron(iii) precursors. A recent report from Fenske and co-workers describes additional synthetic routes to Fe-NR clusters,further demonstrating the generality of the chemistry. 

Our preliminary survey of Fe-NR cluster chemistry reveals strong parallels between imide and sulfide ligation on high-spin iron. The dinuclear, trinuclear, and tetranuclear geometries found in imidoiron clusters all have structural counterparts in fundamental biologically-relevant Fe-S cluster motifs (Figure... 

Chemical differences between imide and sulfide ligand types, however, are substantive and dictate synthetic tactics. In ionic form, N-anions are considerably more basic than sulfur anions [e.g. in DMSO PhNH2, = 30.6 PhSH, 10.3) and, when coordinated to weak-field iron, the former remain more reactive than the latter. Furthermore, redox transformations coupled to weak-field iron are much more accessible with sulfur than nitrogen. As a result, imide ligation is introduced in Scheme 5.9 by protolysis rather than the salt-metathesis or redox routes typical in Fe-S chemistry. Protolysis requires iron precursors with reactive ligands as latent bases the relative instability of these complexes forces the incorporation of imide (or equivalent N-anions) early in the synthetic sequence. 

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