Synthesis of a new 4Fe4S cluster with a biomimetic bulky thiolate ligand as model for the [Fe4S4] states of high potential iron-sulfur proteins

Abstract The new clusters (X) 2 [Fe 4 S 4 (SCH 2 tib 4 ] (XEt 4 N, Ph 4 P) have been synthesized with a sterically encumbered and benzyl-type thiolate ligand, in order to study its influence on the formation and stability of the oxidized state [Fe 4 S 4 ] 3+ . Both clusters exhibit a stable redox couple in CH 2 Cl 2 , and the oxidized (Ph 4 P) [Fe 4 S 4 (SCH 2 tib) 4 ] can be generated in solution by chemical oxidation. EPR and 1 H NMR studies show that this species is unstable in solution at room temperature and that it decomposes, possibly by way of a transient [3Fe4S] + state. The isotropic shift, longitudinal relaxation time and temperature dependence of the SCH 2 protons' resonance have been analyzed both in the [4Fe4S] 2+ and [4Fe4S] 3+ states, and compared to results available on the same oxidation state centers in [4Fe4S] proteins.