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Keywords:

  • N ligands;
  • S ligands;
  • Iron;
  • Crown compounds;
  • Reduction

Abstract

The monomeric {Fe(NO)2}10 dinitrosyliron complexes (DNICs) [K-18-crown-6-ether][(NO)2Fe(NC9H6-NH)] (1), [K-18-crown-6-ether][(NO)2Fe(NC9H6-O)] (2), and [K-18-crown-6-ether][(NO)2Fe(NC9H6-S)] (3) containing [N,NH], [N,O], and [N,S] ligations were synthesized by displacing the N,N,N′,N′-tetramethylethylenediamine (tmeda) group of {Fe(NO)2}10 (tmeda)Fe(NO)2 with quinolin-8-amide, quinolin-8-olate, and quinolin-8-thiolate, respectively. Anionic {Fe(NO)2}10 DNICs 13 were characterized by IR, 1H NMR, and UV/Vis spectroscopy and single-crystal X-ray diffraction. The binding affinity of the ligands (i.e., [NC9H6NH], [NC9H6O], and [NC9H6S]) toward the {Fe(NO)2}10 fragment was also investigated, and ligand substitution was found to follow the order [NC9H6S] > [NC9H6O] > [NC9H6NH]. Displacement of the tmeda group of (tmeda)Fe(NO)2 by [K-18-crown-6-ether][SC6H4-o-NH2] and [PPh4][SC6H4-o-NH2] afforded monomeric {Fe(NO)2}10 DNIC [K-18-crown-6-ether][(NO)2Fe(SC6H4-o-NH2)] (4) and dimeric {Fe(NO)2}10–{Fe(NO)2}10 DNIC [PPh4]2[(NO)2Fe(μ-SC6H4-o-NH2)]2 (5), respectively. The function of the countercation in the formation of monomeric {Fe(NO)2}10 DNIC 4 or dimeric {Fe(NO)2}10–{Fe(NO)2}10 DNIC 5 was also demonstrated upon reduction of the {Fe(NO)2}9 DNICs [cation][(NO)2Fe(SC6H4-o-NH2)2] (6) {cation = K-18-crown-6-ether (6a), [PPh4] (6b)}. In contrast to the formation of thiolate-containing {Fe(NO)2}9 DNICs through nucleophilic cleavage of the bridging thiolates of Roussin's red esters, the transformation of complexes 4 and 5 into complexes 6a and 6b, respectively, in the presence of disulfide provides a new synthetic pathway for the synthesis of thiolate-containing {Fe(NO)2}9 DNICs.