Abstract
Reaction of Fe(CO)2(NO)2 and sparteine/tetramethylethylenediamine (TMEDA) in tetrahydrofuran afforded the electron paramagnetic resonance (EPR)-silent, neutral {Fe(NO)2}10 dinitrosyl iron complexes (DNICs) [(sparteine)Fe(NO)2] (1) and [(TMEDA)Fe(NO)2] (2), respectively. Furthermore,□eaction of [(sparteine)Fe(NO)2] and [PPN][Fe(NO)(S,S-C6H4)2] yielded [PPN][Fe(NO)(S,S-C6H4)2Fe(NO)2]. The cationic {Fe(NO)2}9 complex [(sparteine)Fe(NO)2][BF4] (3) was obtained from the reaction of complex 1 and [NO][BF4] in CH3CN. Reaction of complex 3 and ligands including thiolate, carboxylate, and imidzole species implicated the formation of DNICs. Meanwhile, DNIC or RRE were obtained from the reaction of complex 1/3 and rubredoxin. The stable and isolable anionic {Fe(NO)2}9 DNIC [(S(CH2)3S)Fe(NO)2]- (4), with a bidentate alkylthiolate coordinated to a {Fe(NO)2} motif, was prepared by the reaction of [S(CH2)3S]2- and the complex 3. Transformation from the neutral complex 1 to the anionic complex 4 was verified via the cationic complex 3. Here complex 3 acts as an {Fe(NO)2}-donor reagent in the presence of thiolates. The EPR spectra of complex 3 exhibit an isotropic signal with g = 2.032 at 298 K, respectively, the characteristic g value of {Fe(NO)2}9 DNICs. On the basis of N-O/Fe-N(O) bond lengths of the single-crystal X-ray structures of the {Fe- (NO)2}9/{Fe(NO)2}10 DNICs, the oxidation level of the {Fe(NO)2} core of DNICs can be unambiguously assigned. The mean N-O distances falling in the range of 1.214(6)-1.189(4) □ and the Fe-N(O) bond distances in the range of 1.650(7)-1.638(3) □ are assigned as the neutral {Fe(NO)2}10 DNICs. In contrast, the mean N-O bond distances ranging from 1.178(3) to 1.160(6) □ and the mean Fe-N(O) bond distances ranging from 1.695(3) to 1.661(4) □ are assigned as the anionic/neutral/cationic {Fe(NO)2}9 DNICs. In addition, an EPR spectrum in combination with the IR νNO (the relative position of the νNO stretching frequencies) and their difference NO spectrum may serve as an efficient tool for discrimination of the existence of the anionic/cationic/neutral {Fe(NO)2}9 DNICs and the neutral {Fe(NO)2}10 DNICs.