Comprehensive iron-selenium-thiolate cluster chemistry

Reconstitution of apoferredoxins and other proteins with iron salts and selenide has resulted in the incorporation of Fe{sub n}Se{sub n} clusters in proteins whose native clusters are Fe{sub n}S{sub n} (n = 2,4). These nonnative clusters have proven useful in interpreting certain electronic features of native cluster, and tend to occur in high-spin' forms (S {ge} 1/2). These observations have prompted investigation of a comprehensive set of Fe-Se-SR clusters. Reaction of (Et{sub 4}N){sub 2}(Fe(SEt){sub 4}) with 1 equiv of elemental Se in acetonitrile affords (Et{sub 4}N){sub 2}(Fe{sub 2}Se{sub 2}(SEt){sub 4}) (1, 55%). Ligand substitution of 1 with 4 equiv of PhSH gives (Et{sub 4}N){sub 2}(Fe{sub 2}Se{sub 2}(SPh){sub 4}) (2, 72%). Reaction of (Et{sub 4}N){sub 2}(Fe(SEt){sub 4}) with 1.4 equiv of elemental Se in acetone gives (Et{sub 4}N){sub 3}(Fe{sub 3}Se{sub 4}(SEt){sub 4}) (3, 67%), which with PhSH is converted to (Et{sub 4}N){sub 3}(Fe{sub 3}Se{sub 4}(SPh){sub 4}) (4, 66%). The reaction system FeCl{sub 3}/Se/4NaSEt in ethanol assembles (Et{sub 4}N){sub 2}(Fe{sub 4}Se{sub 4}(SEt){sub 4}) (5, 66%). The (Fe{sub 4}({mu}{sub 3}-Se){sub 4}){sup 2+} core has the familiar cubane stereochemistry with a compressed tetragonal distortion from cubic symmetry. Reduction of 3 with Zn in acetonitrile or 5 with sodium acenaphthylenide in THF/acetonitrile gives (Et{sub 4}N){sub 3}(Fe{sub 4}Se{sub 4}(SEt){sub 4}) (6, 56-68%). The reaction system FeCl{sub 3}/Na{sub 2}Se{sub 2}/3NaSEt assembles (Et{sub 4}N){sub 4}(Fe{sub 6}Se{sub 9}(SEt){sub 2}) (7, 68%). Of all properties, isotropic shifts most readily distinguish Fe-S and Fe-Se clusters of the same nuclearity. Comparison of the structures of (Fe{sub 4}Q{sub 4}){sup 2+} structures (Q = S, Se) provides strong evidence that a compressed tetragonal geometry is the intrinsically preferred structure of this oxidation state.