New Members of a Class of Monomeric {Fe(NO)₂}¹⁰ Dinitrosyliron Complexes and a Dimeric {Fe(NO)₂}¹⁰–{Fe(NO)₂}¹⁰ Dinitrosyliron Complex

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 1–3 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.