Facile access to tetra-substituted FeIIFeII biomimetics for the oxidized state active site of [FeFe]-hydrogenases

Abstract

In this study, we present a convenient method to obtain two types of novel tetra-substituted Fe/Se salts through a dehalogenation reaction, aiming to advance research on mimicking the Fe^IIFe^II oxidation state of [FeFe]-H₂ases. Initially, by treating [Fe₂(μ-SeBn)₂(CO)₄(dppv)] (Bn = CH₂C₆H₅, dppv = cis-1,2-bis(diphenylphosphino)ethylene) with one equivalent of dppv under UV and reflux conditions, the neutral Fe^IFe^I and Fe^IIFe^II precursors [Fe₂(μ-SeBn)₂(CO)₂(dppv)₂] (1) and [Fe₂(μ-SeBn)₂(μ-Se)(CO)₂(dppv)₂] (2) were successfully isolated in good yields. Subsequently, 1 underwent dehalogenation reactions with halocarbons (such as CCl₄ and CBr₄) or I₂, leading to the formation of tetra-substituted salts [Fe₂(μ-SeBn)₂(μ-X)(CO)₂(dppv)₂]⁺ (X = Cl, Br, and I) ([3]Cl, [4]Br and [5]I₃). GC-MS analysis of the reaction with carbon tetrachloride detected the formation of the homo-coupled product CCl₃–CCl₃ (m/z = 235), indicating the presence of a CCl₃˙ species. Notably, 2 also exhibited intriguing reactivity with R–X and I₂. Unlike 1, the reaction of 2 with RX or I₂ involved cleavage of the C–Se bond, leading to the isolation of [Fe₂(μ-SeBn)(μ-Se₂)(CO)₂(dppv)₂]⁺X⁻ (X = Cl, Br, I₃) ([6]Cl, [6]Br and [6]I₃) in good yields. The reaction involved debenzylation of 2 and was confirmed by GC-MS detection of C₆H₅CH₂CCl₃ (m/z = 208) in the reaction with CCl₄, suggesting a radical pathway.