Synthesis and reactivity of the five-coordinate {Fe(NO)2}9 [(TMEDA)Fe(NO)2I]

The reaction of [Fe(μ-I)(NO)2]2 and TMEDA in a 1:2 molar ratio in THF affords the neutral five-coordinate DNIC [(TMEDA)Fe(NO)2I] (1). The single-crystal X-ray structure shows that the geometry of iron center of complex 1 is best described as a distorted trigonal bipyramidal with two nitrosyl groups positioned in the equatorial plane. The EPR spectrum of complex 1 displays the six-line signal with g = 2.031 (aI = 37.6 G) at 298 K. The coincident g values of EPR among complex 1, protein-bound DNICs and low-molecular-weight DNICs implicate that the five-coordinate DNICs may exist in biological system. The interconversion between complex 1 and [(TMEDA)Fe(NO)2] (2) reveals that the {Fe(NO)2}9 DNICs containing [amine, amine] ligation mode could be stabilized by the five-coordinated geometry while the {Fe(NO)2}10 DNICs containing [amine, amine] ligation mode favors the four coordination sphere. In addition, the transformation from complex 1 to [Fe(NO)2(C3H3N2)]4 (3), [Fe(μ-SPh)(NO)2]2 (4), [PPh4][(PhS)2Fe(NO)2] (5) and [Na-18-crown-6-ether][(C3H3N2)2Fe(NO)2] (6), respectively, in the presence of thiolates or imidazolates indicates that complex 1 could be employed as the precursor for the syntheses of the DNICs containing the [N,N]/[N,S]/[S,S] different ligations.

Graphical abstractThe interconversion between the five-coordinate {Fe(NO)2}9 [(TMEDA)Fe(NO)2I] and four-coordinate {Fe(NO)2}10 [(TMEDA)Fe(NO)2] is demonstrated via the reduction with CoCp2 and oxidation with I2, respectively.Figure optionsDownload full-size imageDownload as PowerPoint slide