Electronic Structure of Nitric Oxide Adducts of Bis(diaryl-1,2-dithiolene)iron Compounds:  Four-Membered Electron-Transfer Series [Fe(NO)(L)₂]^z(z= 1+, 0, 1−, 2−)

Abstract

Four members of the electron-transfer series [Fe(NO)(S(2)C(2)R(2))2]z (z = 1+, 0, 1-, 2-) have been isolated as solid materials (R = p-tolyl): [1a](BF4), [1a]0, [Co(Cp)2][1a], and [Co(Cp)2]2[1a]. In addition, complexes [2a]0 (R = 4,4-diphenyl), [3a]0 (R = p-methoxyphenyl), [Et(4)N][4a] (R = phenyl), and [PPh(4)][5a] (R = -CN) have been synthesized and the members of each of their electron-transfer series electrochemically generated in CH(2)Cl(2) solution. All species have been characterized electro- and magnetochemically. Their electronic, Mössbauer, and electron paramagnetic resonance spectra as well as their infrared spectra have been recorded in order to elucidate the electronic structure of each member of the electron-transfer series. It is shown that the monocationic, neutral, and monoanionic species possess an {FeNO}6 (S = 0) moiety where the redox chemistry is sulfur ligand-based, (L)2-(L*)1-: [Fe(NO)(L*)2]+ (S = 0), [Fe(NO)(L*)(L)]0 <--> [Fe(NO)(L)(L*)]0 (S = 1/2), [Fe(NO)(L)2]- (S = 0). Further one-electron reduction generates a dianion with an {FeNO}7 (S = 1/2) unit and two fully reduced, diamagnetic dianions L2-: [Fe(NO)(L)2]2- (S = 1/2).

Influence of Thiolate Ligands on Reductive N−O Bond Activation. Probing the O2− Binding Site of a Biomimetic Superoxide Reductase Analogue and Examining the Proton-Dependent Reduction of Nitrite

“…The extremely short Fe–X (X= NO) bond of 2 (Table 2) reflects the highly covalent nature of the Fe–NO bond. 18,27 This bond length is comparable to the DFT calculated distance in IPNS Fe-NO, 16 is slightly above the range typical for {FeNO} 7 species (1.68–1.76 Å), and well above that of {FeNO} 6 species (1.63–1.67 Å), 18,28,32,34–40 including [Fe(S 2 Me2 N 3 (Pr,Pr))(NO)] + ( 6 , Fe–NO= 1.676(3) Å). 26 The N-O bond length (1.118(6) Å) in 2 is closer to that of free NO (1.15 Å) than to NO − (1.26 Å), and is unexpectedly shorter than that of 6 (1.161(4) Å), despite the presence of an additional electron in the π*-manifold of {FeNO} 7 2 versus {FeNO} 6 6 .…”

“…8,11,30,33 Whereas compounds with the Fe(II)-NO• electron distribution are typically S= ½, and are usually described as containing a low-spin (S= 0) Fe(II) ligated by (S= ½.) NO•, 28,29,32,45 although the electronic description of these compounds is more controversial. 31 Compound 2 is intermediatespin S= 3/2 ( vide infra ), suggesting that the former description might be more accurate, despite the fact that the ν NO frequency falls below that of an Fe(III)-NO − compound.…”

Spectroscopic and Computational Characterization of the NO Adduct of Substrate-Bound Fe(II) Cysteine Dioxygenase: Insights into the Mechanism of O2 Activation

“…58, 59 While the third synthetic complex features two mono-anionic dithiolene ligands in addition to the nitrosyl ligand, its square-pyramidal ligand environment bears little resemblance to the CDO active site. 63 …”

Chemistry of Bound Nitrogen Monoxide and Related Redox Species

“…radical. 103 Unfortunately, no crystal structure is available in order to put in evidence the predictable bending of FeNO in [1a] 2À . L 1 ¼ S 2 C 2 R 2 , R ¼ p-tolyl.…”