Preparation and structural characterization of [K(18-crown-6)]+ salts of [RNSN]- anions and the [NSN]2- dianion

[K(18-crown-6)](+) salts of the [RNSN](-) anions (R = Alk, Ar) and the [NSN](2-) dianion, which are thermally stable and very soluble in aprotic organic solvents, were prepared from [K(18-crown-6)](+)[tBuO](-) and the corresponding R-N=S= N-SiMe3 and (Me3Si-N=)(2)S, respectively. The salts are characterized by multinuclear (H-1, C-13, N-14, F-19, Si-29 and K-39) NMR spectroscopy in solution and by X-ray diffraction in the solid state. The experimentally determined bond lengths confirm that the [RNSN](-) anions are thiazylamides, R-N--Sequivalent toN rather than sulfur diimides, R-N=S=N-. Relative to O=S=O, in the [NSN](2-) dianion, which is the genuine aza-analogue of sulfur dioxide, the bond lengths are elongated and the bond angle is widened. This might reflect electrostatic repulsion between the negatively charged N atoms. The experimental results are in agreement with theoretical calculations (RHF, B3LYP, MP2). In the nitrogen NMR spectra, when going from [AlkNSN](-) to [ArNSN](-), the low-field signal of the terminal (unsubstituted) N atom reveals further deshielding, whereas the high-field signal of the internal (substituted) N atom displays further shielding. The N-14 NMR resonance for the [NSN](2-) dianion is practically insensitive to the counterion. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).