A Synthetic Model of Enzymatic [Fe₄S₄]-Alkyl Intermediates

Although alkyl complexes of [Fe₄S₄] clusters have been invoked as intermediates in a number of enzymatic reactions, obtaining a detailed understanding of their reactivity patterns and electronic structures has been difficult owing to their transient nature. To address this challenge, we herein report the synthesis and characterization of a 3:1 site-differentiated [Fe₄S₄]²⁺-alkyl cluster. Whereas [Fe₄S₄]²⁺ clusters typically exhibit pairwise delocalized electronic structures in which each Fe has a formal valence of 2.5+, Mössbauer spectroscopic and computational studies suggest that the highly electron-releasing alkyl group partially localizes the charge distribution within the cubane, an effect that has not been previously observed in tetrahedrally coordinated [Fe₄S₄] clusters.