Insight into the Dinuclear {Fe(NO)₂}¹⁰{Fe(NO)₂}¹⁰ and Mononuclear {Fe(NO)₂}¹⁰ Dinitrosyliron Complexes

Abstract

The reversible redox transformations [(NO)(2)Fe(S(t)Bu)(2)](-) ⇌ [Fe(μ-S(t)Bu)(NO)(2)](2)(2-) ⇌ [Fe(μ-S(t)Bu)(NO)(2)](2)(-) ⇌ [Fe(μ-S(t)Bu)(NO)(2)](2) and [cation][(NO)(2)Fe(SEt)(2)] ⇌ [cation](2)[(NO)(2)Fe(SEt)(2)] (cation = K(+)-18-crown-6 ether) are demonstrated. The countercation of the {Fe(NO)(2)}(9) dinitrosyliron complexes (DNICs) functions to control the formation of the {Fe(NO)(2)}(10){Fe(NO)(2)}(10) dianionic reduced Roussin's red ester (RRE) [PPN](2)[Fe(μ-SR)(NO)(2)](2) or the {Fe(NO)(2)}(10) dianionic reduced monomeric DNIC [K(+)-18-crown-6 ether](2)[(NO)(2)Fe(SR)(2)] upon reduction of the {Fe(NO)(2)}(9) DNICs [cation][(NO)(2)Fe(SR)(2)] (cation = PPN(+), K(+)-18-crown-6 ether; R = alkyl). The binding preference of ligands [OPh](-)/[SR](-) toward the {Fe(NO)(2)}(10){Fe(NO)(2)}(10) motif of dianionic reduced RRE follows the ligand-displacement series [SR](-) > [OPh](-). Compared to the Fe K-edge preedge energy falling within the range of 7113.6-7113.8 eV for the dinuclear {Fe(NO)(2)}(9){Fe(NO)(2)}(9) DNICs and 7113.4-7113.8 eV for the mononuclear {Fe(NO)(2)}(9) DNICs, the {Fe(NO)(2)}(10) dianionic reduced monomeric DNICs and the {Fe(NO)(2)}(10){Fe(NO)(2)}(10) dianionic reduced RREs containing S/O/N-ligation modes display the characteristic preedge energy 7113.1-7113.3 eV, which may be adopted to probe the formation of the EPR-silent {Fe(NO)(2)}(10)-{Fe(NO)(2)}(10) dianionic reduced RREs and {Fe(NO)(2)}(10) dianionic reduced monomeric DNICs in biology. In addition to the characteristic Fe/S K-edge preedge energy, the IR ν(NO) spectra may also be adopted to characterize and discriminate [(NO)(2)Fe(μ-S(t)Bu)](2) [IR ν(NO) 1809 vw, 1778 s, 1753 s cm(-1) (KBr)], [Fe(μ-S(t)Bu)(NO)(2)](2)(-) [IR ν(NO) 1674 s, 1651 s cm(-1) (KBr)], [Fe(μ-S(t)Bu)(NO)(2)](2)(2-) [IR ν(NO) 1637 m, 1613 s, 1578 s, 1567 s cm(-1) (KBr)], and [K-18-crown-6 ether](2)[(NO)(2)Fe(SEt)(2)] [IR ν(NO) 1604 s, 1560 s cm(-1) (KBr)].

Chelate‐Thiolate‐Coordinate Ligands Modulating the Configuration and Electrochemical Property of Dinitrosyliron Complexes (DNICs)

“…[7] The stabilityo fc omplex 1 may be ascribed to thec helating effect of the pdt ligand to optimize (modulate) the ironÀsulfur bonding of the {Fe(NO) 2 NO. Due to the extremely low n NO stretching frequency [ñ = 1461 cm À1 (m-NO)], the electronic structure of the bridging NO ligand may be assigned as an itroxyl anion (NO À ).…”

“…The distorted dihedral angle of the [2Fe2S] core of complex 5b (dihedral angle 1278)i ss maller than that of the observed dianionic reduced RRE [Fe(m-StBu)(NO) 2 ] 2 2À (dihedral angle 1398). [7] Presumably,t he long Fe···Fe distance of 3.215 i se mployed to relieve the electronic richnesso ft he {Fe(NO) 2 } 10 -{Fe(NO) 2 } 10 core. The molecular structure of complex 6 is shown in Figure 7.…”

“…Complex 2,c ontaining the shorter backbone length, displays the pre-edge energy at 7113.3 eV,f alling within the reported range of 7113.1-7113.3 eV for {Fe(NO) 2 } 10 DNICs. [7] The SK -edge spectra of complexes[ (NO) 2 Fe(S(CH 2 ) 3 …”

“…The chemical redox reactions, electrochemistry,a nd extended transition state and natural orbitalsf or chemical valence (ETS-NOCV) analysis of {Fe(NO) 2 } and the electrochemical redox potentialo ft he DNICs. The Fe K-edge pre-edge energy and SK -edge XAS demonstrate that the oxidation of complex 1 yielding[(NO) 2 Fe(S(CH 2 ) 3 2À in the polar organic solvent( CH 3 CN), [7] the reduction of the {Fe(NO) 2 } 9 DNIC [(NO) 2 Fe(S(CH 2 ) 3 S)] À bearing ac helate pdt ligand by [KC 8 ]+ +[18-crown-6-ether]g enerates the monomeric {Fe(NO) 2 } 10 reduced-formD NIC 1 with the coordination sphere retained (Scheme1b), characterizedb yI R spectroscopy,c yclic voltammogram (CV), X-ray absorption spectroscopy (XAS), and single-crystal X-ray diffractiona nalysis. Upon reduction of the {Fe(NO) 2 } 9 DNIC [(NO) 2 Fe(S(CH 2 ) 3 S)] À in CH 3 CN at 0 8C, [4e] the IR spectrum (n NO )r eveals as ignificant shift from ñ = 1718 (s), 1674 cm À1 (vs) to ñ = 1600 (s), 1552 cm À1 (vs) in CH 3 CN, demonstrating the formation of the {Fe(NO) 2 } 10 DNIC 1 (see Figure S1 in the Supporting Information).…”

Recent advances in multinuclear metal nitrosyl complexes

“…Compound 21 is best described as {Fe(NO) 2 } 10 -{Fe(NO) 2 } 10 according to the Enemark - Feltham notation. This µ-oxo diiron compound can be converted to RRE 2− by addition of [St-Bu] − [107]. …”