Preparation and Structural Characterization of [K(18‐crown‐6)]+ Salts of [RNSN]− Anions and the [NSN]2− Dianion

Abstract

Abstract[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=)2S, respectively. The salts are characterized by multinuclear (1H, 13C, 14N, 19F, 29Si and 39K) 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−−S≡N 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 14N NMR resonance for the [NSN]2− dianion is practically insensitive to the counterion. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)