Anionic Roussin’s Red Esters (RREs) syn-/anti-[Fe(µ-SEt)(NO)₂]₂⁻: the Critical Role of Thiolate Ligands in Regulating the Transformation of RREs into Dinitrosyl Iron Complexes and the Anionic RREs

Abstract

The anionic syn-/ anti-[Fe(mu-SEt)(NO) 2] 2 (-) ( 2a) were synthesized and characterized by IR, UV-vis, EPR, and X-ray diffraction. The geometry of the [Fe(mu-S) 2Fe] core is rearranged in going from [{Fe(NO) 2} (9)-{Fe(NO) 2} (9)] Roussin's red ester [Fe(mu-SEt)(NO) 2] 2 ( 1a) (Fe...Fe distance of 2.7080(5) A) to the [{Fe(NO) 2} (9)-{Fe(NO) 2} (10)] complex 2a (Fe...Fe distance of 2.8413(6) A) to minimize the degree of Fe...Fe interaction to stabilize complex 2a. On the basis of X-ray absorption (Fe K- and L-edge), EPR and SQUID, complex 2a is best described as the anionic [{Fe(NO) 2} (9)-{Fe(NO) 2} (10)] Roussin's red ester with the fully delocalized mixed-valence core. The complete bridged-thiolate cleavage yielded DNIC [(EtS) 2Fe(NO) 2] (-) ( 3a) in the reaction of 2 equiv of [EtS] (-) and complex 1a, whereas reaction of 2 equiv of [(t)BuS] (-) with [Fe(micro-S (t)Bu)(NO) 2] 2 (1b) gave DNIC [((t)BuS) 2Fe(NO) 2] (-) (3b) and the anionic Roussin's red ester [Fe(mu-S (t)Bu)(NO) 2] 2 (-) (2b) through bridged-thiolate cleavage in combination with reduction. In contrast to the inertness of DNIC 3b toward complex 1b, nucleophile DNIC 3a induces the reduction of complex 1a to produce the anionic Roussin's red ester 2a. Interestingly, dissolution of complex 3a in MeOH at 298 K finally led to the formation of a mixture of complexes 2a and 3a, in contrast to the dynamic equilibrium of complexes 3b and 1b observed in dissolution of complex 3b in MeOH. These results illustrate the aspect of how the steric structures of nucleophiles ([EtS] (-) vs [ (t)BuS] (-) and [(EtS) 2Fe(NO)2](-) vs [((t)BuS) 2Fe(NO)2] (-)) function to determine the reaction products.

Redox conversions of dinitrosyl iron complexes with natural thiol-containing ligands

“…= 2.0, these authors associate it with B-DNIC able to accept only one electron. In the framework of this hypothesis, the electronic configuration of two iron atoms in B-DNIC changes from d 9 -d 9 ({Fe(NO) 2 } 9 -{Fe(NO) 2 } 9 ) to d 9 -d 10 ({Fe(NO) 2 } 9 -{Fe(NO) 2 } 10 ), while the antiferromagnetic interactions between two Fe(NO) 2 groups favor the conversion of B-DNIC into the paramagnetic form (S = ½) [12,14,15].…”

13. Reactivity of iron-sulfur clusters with nitric oxide

“…The salt and ester are often considered together as they are related by structure. The oneelectron reduced form of the ester is also known, is EPR active with S=1/2, and features a slightly elongated Fe-Fe distance [83].…”

Mechanisms of Nitric Oxide Reactions Mediated by Biologically Relevant Metal Centers

“…The structures drawn in Fig. 2 are qualitative representations of structures that have been determined using X-ray crystallography [35][36][37][38].…”

“…Notably, the complex is not very stable, and NO readily dissociates from the Cu coordination site. Table 1 summarizes some structural and IR spectral data for examples of heme and non-heme iron nitrosyls and of copper nitrosyls [17,18,[36][37][38][39][40][41][42][43][44][45][46].…”