Iron-Imide Cluster Chemistry

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. 

When the self-assembly reaction is conducted in toluene, a different product distribution is obtained. Neutral cluster products are still formed in low yields however, terminal imide cluster 7 is now the predominant neutral species, with chlorocubane 5 virtually absent as judged by NMR spectroscopy. The 

The presence of lithium chloride alters the chemistry, presumably by coordination to intermediary species during cluster self-assembly. Thus, the addition of one equivalent of LiCl to 9 yields the chloride adduct 12 further treatment with one equivalent of r-butylamine leads to neutral cubane 5, but at a much reduced rate compared to the reaction without LiCl. The reaction with aniline is also retarded in the presence of LiCl, and the formation of azobenzene is significantly diminished. We have identified three products from this reaction 

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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... 

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... 

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