Interaction of Nitric Oxide with Tetrathiolato Iron(II) Complexes: Relevance to the Reaction Pathways of Iron Nitrosyls in Sulfur-Rich Biological Coordination Environments

The mechanism of formation of dinitrosyl iron complexes (DNICs) coordinated by cysteine residues at iron−sulfur protein sites has received little attention in the chemical literature. As a logical first step toward elucidating this mechanism and characterizing new iron−nitrosyl intermediates, we investigated the interaction of NO (g) and NO+ with iron−sulfur complexes chosen to mimic sulfur-rich iron sites in biology. The reaction of NO (g) with [Fe(StBu)4]2- cleanly affords the mononitrosyl complex, [Fe(StBu)3(NO)]- (1), a previously unknown species evoked in this chemistry. Reaction of [Fe(StBu)4]2- with NO derivatives, such as NO+, yields the corresponding dinitrosyl S-bridged Roussin red ester [Fe2(μ-StBu)2(NO)4] (2). The nitrosyl complexes 1 and 2 can chemically convert to the DNIC, [Fe(StBu)2(NO)2]- (3). The results should aid in the spectroscopic identification and elucidation of reaction pathways for the nitrosylation of iron in biologically related sulfur-rich coordination environments.