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

The reaction of [Fe(mu-I)(NO)(2)](2) and TMEDA in a 1:2 molar ratio in THF affords the neutral five-coordinate DNIC [(TMEDA)Fe(NO)(2)I] (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 (a(I) = 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(mu-SPh)(NO)(2)](2) (4), [PPh4][(PhS)(2)Fe(NO)(2)] (5) and [Na-18-crown-6-ether][(C3H3N2)(2)Fe(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. (C) 2009 Elsevier B.V. All rights reserved.