Anionic/Neutral Dinitrosyl Iron Complexes (DNICs) Containing [S,S]/[S,N]/[S,O] Ligation Modes: Synthesis and Electronic Structure Study of {Fe(NO)2} Core

• Main Authors: Tsai, Ming-Li, 蔡明利
• Other Authors: Liaw, Wen-Feng
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/23143961087120015743

博士 === 國立清華大學 === 化學系 === 97 === Roussin’s red esters [Fe(μ-SR)(NO)2]2 (RREs) were synthesized to delineate the interconversion among the anionic/neutral {Fe(NO)2}9 DNICs and RREs. In contrast to the bridged-thiolate cleavage yielding the neutral {Fe(NO)2}9 [(SC6H4-o-NHCOPh)(Im)Fe(NO)2] (2) (Im = imidazole) by reacting 2 equiv of imidazole with [Fe(μ-SC6H4-o-NHCOPh)(NO)2]2 (1), addition of the Lewis base [OPh]– to the THF solution of complex 1 and [Fe(μ-SC6H4-o-COOH)(NO)2]2 (4) yielded the EPR-active, anionic {Fe(NO)2}9 [(SC6H4-o-NCOPh)Fe(NO)2]– (5) and [(SC6H4-o-COO)Fe(NO)2]– (6) with the anionic [SC6H4-o-NCOPh]2– (S,N-bonded) and the anionic [SC6H4-o-COO]2– (S,O-bonded) ligands bound to the {Fe(NO)2} core in a bidentate manner, respectively. Complexes 1-5 were characterized by IR, UV-vis, EPR, and single-crystal X-ray diffraction. Detailed examinations of the EPR (the pattern at room temperature and 77 K) and IR spectra (the relative position of the νNO stretching frequencies) of these complexes indicates that the EPR spectrum in combination with the IR νNO spectrum may serve as an efficient tool for the discrimination of the different binding modes of anionic {Fe(NO)2}9 DNICs, the neutral {Fe(NO)2}9 DNICs, and Roussin’s red ester. Also, the ligand frameworks provide an opportunity to demonstrate the possible binding modes of Fe(NO)2 fragment in polypeptide chain or cysteine-containing biomolecules possessing the biological HScys-X-X-L (L = -NHC(O)R, -C(O)OH) motif. The detailed DFT calculations further elucidate that the modulations of electronic structures via geometrical constraints on the {Fe(NO)2}9 core, i.e. increase/decrease of the S-Fe-S chelating angles of [(S(CH2)3S)Fe(NO)2]–, might adopt three redox-couples ({Fe(NO)2}8 {Fe(NO)2}9 {Fe(NO)2}10) and accompanied by the formations the localized sulfide radical species in the {Fe(NO)2}8 DNICs/ delocalized thiyl radical species in the {Fe(NO)2}10 DNICs, respectively. This extraordinary phenomenon may result from the inter-electron-transfer among redox-active Fe center, thiolate and NO ligands by tuning the ligand filed strength. The modulations of electronic structures ({FeI(NO•)2}, {FeII(NO•)(NO—)}, and {FeIII(NO—)2}) derived from [S/S], [S/N, S/O, N/N], [O/O] ligation modes, respectively, would preserve the {Fe(NO)2}9 core. Based on the ESI-MS and IR 轩NO stretching frequencies data, a potential specific-targeting RREs ([Fe(μ-SC2H4C(O)NH-2-deoxyglucosamide)2(NO)2]2 (8) was successfully synthesized by the amide-bond formation between the COOH end on the [Fe(贡-SC2H4COOH)(NO)2]2 (7) and the NH2 end on the glucosamine.