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(mu-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.