| The syntheses, from ferric precursors, of weak field, high spin iron-imide (Fe-NR) clusters in three core motifs—dinuclear [Fe2(μ-NR) 2]2+ (R = tBu, Mes, Ph, p-Tol), trinuclear [Fe3(μ-NR)4]2+ (R = Ph, p-Tol), and tetranuclear [Fe4(μ 3-NR)4]z+ (R,z = tBu, 3–7; Ph, 2)—are described. Clusters are characterized by single crystal X-ray crystallography, cyclic voltammetry, and UV-Vis, 1H NMR and MOssbauer spectroscopies.; Protonolysis by primary amines of FeCl[N(SiMe3)2] 2(THF) (3) and [FeCl2{lcub}N(SiMe3) 2{rcub}2]− (4) is a useful route to dinuclear, trinuclear, and tetranuclear iron-arylimide clusters and the iron-alkylimides Fe4(μ3-NtBu) 4Cl2(NtBu)2 ( 15) and Fe2(μ-NtBu) 2Cl2(NH2tBu) 2 (16). The use of the chloride sources—LiCl and R4NCl(R = n-Bu, Et)—to generate 4 from 3 suppresses redox chemistry that leads to the production of azoarenes during protonolysis. The reaction of FeCl3 and 2 equivalents of LiNHtBu generates the remaining tetranuclear iron-alkylimides, including Fe4(μ3-N tBu)4Cl4 (11) and Fe 4(μ3-NtBu)4Cl 3(NtBu) (13), in a mixture of products that is separated by utilizing the redox and solubility properties of the compounds. The first observed stable terminal imide bound to iron is found in 13.; Core and terminal ligand replacement of 16 results in the production of several new dinuclear iron-alkylimide compounds, including (Et4N) 2[Fe2(μ-NtBu)2Cl 4] (14) and Fe2(μ-NtBu) 2[N(SiMe3)2]2 (20), which contains two trigonal planar iron sites. The core-bound imides of [Fe 4(μ3-NPh)4Cl4]2− (10), 14, and 16, are found to exchange with free arylamines in solution, and 10 is found to catalytically disproportionate arylhydrazines into their respective azoarenes and arylamines. Replacement of core-bound imide with sulfide results in the first synthesis of weak-field, high spin iron-imide-sulfide (Fe-NR-S) clusters, including (Et4N)2[Fe4(μ3-N tBu)2(μ3-S)2Cl4 ] ([Et4N]27) and (Et4N)2[Fe 2(μ-NtBu)(μ-S)Cl4] ([Et4N]29).; The structures of the Fe-NR and Fe-NR-S complexes are homologous to fundamental iron-sulfur (Fe-S) cluster motifs. The analogy to Fe-S chemistry also encompasses parallels between Fe-mediated redox transformations of nitrogen and sulfur ligands and reductive core conversions of linear dinuclear and trinuclear clusters to heterocubane species. The correspondence of nitrogen and sulfur chemistry at iron is intriguing in the context of speculative Fe-mediated mechanisms... |
