Chemical and electrochemical interrelationships of the 1-Fe, 2-Fe, and 4-Fe analogs of the active sites of iron-sulfur proteins

Abstract

Previous studies of the reactivity properties of the complexes [Fe2S2(SR)4]2~a nd [Fe4S4(SR)4]2" have demonstrated the occurrence of thiolate ligand substitution reactions with retention of Fe2S2 and Fe4S4 core structures. Described in this report are reactions which provide chemical and electrochemical interrelationships of 1-Fe, 2-Fe, and 4-Fe synthetic analogues of the active sites of iron-sulfur proteins. These reactions include (i[Fe4S4(SPh)4]3~by electrochemical reactions; and (iii) tetranuclear dianion-tetranuclear trianion chemical reduction, [Fe4S4(SR)4]2" -* [Fe4S4(SR)4]3". These transformations are correlated with prior synthetic and ligand-exchange processes to provide an overall reaction scheme starting with a simple iron(II) salt, progressing through intermediate 1-Fe and 2-Fe species and terminating in the 4-Fe complexes with cubane-type stereochemistry. Reaction iii was accomplished using sodium acenaphthylenide in hexamethylphosphoramide as reductant. The product trianion was obtained as oxygen-sensitive, crystalline Me4N+ or Et4N+ salts and is an analogue of the 4-Fe active sites of reduced ferredoxin proteins. With its isolation synthetic analogues of five of the seven known physiological proteins have been obtained in substance.

Initial synthesis and structure of an all-ferrous analogue of the fully reduced [Fe 4 S 4 ] 0 cluster of the nitrogenase iron protein

“…2; selected interatomic distances are collected in (18)(19)(20)(21)(22)(23). The volumes in Table 2 were calculated from atomic coordinates (24) 6 , for which v CN ϭ 2,116 and 2,041 cm Ϫ1 , respectively. To the extent that the trends in stretching frequencies are parallel, the data for the clusters support reduction to the all-ferrous state, in which there appears to be sufficient electron donation into the * orbitals of the ligand to reduce v CN to Ͻ2,058 cm Ϫ1 , the value for (Bu 4 N)(CN).…”

Biomimetic Multifunctional Porous Chalcogels as Solar Fuel Catalysts

“…In solution, this reduction is always irreversible. 17 However, the all-ferrous state of the cluster could be more easily stabilized when bound in the chalcogel. When the gels are prepared without Fe 4 S 4 clusters, we see no comparable redox events ( Figure 2B).…”

Stabilities of cubane type [Fe4S4(SR)4]2− clusters in partially aqueous media

“…We designate these clusters as [Fe 4 S 4 {β-CD-(SC 6 H 4 S)} 4 ] 2− ( 18 ) and [Fe 4 S 4 {β-CD-(SC 6 H 4 S) 2 } 2 ] 2− ( 19 ), respectively, following published structural depictions. While these are unproven, absorption spectra and redox potentials are fully consistent with coordination of four arylthiolates to [Fe 4 S 4 ] 2+ as in [Fe 4 S 4 (SPh) 4 ]2 − [37]. Cluster 19 is proposed to have a structure in which two bidentate dithiolates bind to the same cluster, an arrangement unproven in any Fe 4 S 4 cluster.…”

“…In polar organic solvents, clusters with aliphatic thiolate ligands present absorption bands near 300 nm (ε M ~ 22,000) and 420 nm (ε M ~ 17,000) and those with aromatic thiolate ligands a band near 450 nm (ε M ~ 17,000) [36,37]. Addition of water (≲10% v/v) tends to cause small blue shifts of the visible feature and variable but small intensity changes.…”