[2Fe-2S] cluster, 2 and the first candidate of [2Fe-2Se] cluster, 3, were successfully synthesized. Where, L- = 2-((S)-(-)-1-phenylethylimino)-4-(2,6-diisopropylphenylimido)pentane), cod = 1,5-cyclooctadiene and E = sulfur or selenium. All metal complexes were characterized by using X-ray crystallography, 1H-NMR and cyclic voltammetry. 1H NMR and crystallographic data of 2 and 3 agrees with the only reported synthetic [2Fe-2S] clusters, in that both possess high-spin Fe3+ centers. Electrochemical studies of complex 2 showed multiple quasi-reversible redox events, whereas 3 shows only one, suggesting its ability to perform multielectron exchange reactions. Kinetic experiments were carried out to explore the activation parameters for the reaction of elemental sulfur and selenium with complex 1. These reactions were monitored using UV-Visible spectroscopy. Kinetic isotopic effect (KIE) for the S atom transfer reaction is 1.036, which reflects the S-S bond breaking involvement in the reaction, and this also agree with the ΔH‡ = 17.18 kJ/mol. The ΔS‡ = -182 J/molK, may be due to the formation of a highly ordered intermediate state in S8 activation reaction. 1 may act as a catalyst for S or Se atom transfer reactions in 2 and 3 to external substrate like PPh3.

Synthesis, characterization, and kinetic studies of [2Fe-2E] (E = S, Se) model complexes

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