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)

Structures and EPR spectra of binary sulfur–nitrogen radicals from DFT calculations

“…The second published spectrum assigned to this radical has aN = 1.12 mT, but with much narrower lines which also allowed for observation of 33 S coupling of ~0.5 mT at high gain [4]. However, due to the extremely low natural abundance of 33 Figure 3 shows simulations, using hfc values from our calculations, which predict the appearance of the spectra of this radical at natural abundances of the isotopes and with 33 S enrichment. While the former is indistinguishable in appearance from the many reported spectra for radicals containing one 14 N nucleus, the latter has clearly identifiable patterns unique to radicals involving hyperfine coupling to one 14 N and two 33 S nuclei.…”

“…• using the calculated isotropic hfc constants (a) with natural abundances of the isotopes and (b) with 99% enrichment in 33 S. Lineshapes have a 30% Gaussian admixture and typical, rather broad, linewidths of 0.12 mT.…”

“…The only binary S,N species for which 33 S data was available at that time was the [S3N2] +• cation radical, which is also the only binary radical for which the full g and a tensor components have been determined from measurements of anisotropic spectra [5]. An earlier review by Oakley discusses the redox properties of sulfur-nitrogen compounds -including free radicals -in the context of their fundamental chemical and electronic properties [6].…”

Fluoride ion transfer and stabilisation of reactive ions

“…TAS þ ArNSN À decomposes readily at low temperatures, (18-crown-6-K þ ) salts are stable at room temperature, they are useful reagents. Even the dianion SN 2 2À can be stabilised [96].…”

Fundamental chemistry of binary S,N and ternary S,N,O anions: analogues of sulfur oxides and N,O anions

“…2). 39 In the solid state the NSN 2dianion exhibits modestly longer S-E bond lengths compared to the corresponding distances in the isoelectronic SO2 molecule (E = N, 1.484(3) Å; E = O, 1.4297(4) Å). The E-N-E bond angle (E = N, 129.9(2) o ; E = O, 117.5(1) o ) is significantly widened in the dianion, presumably as a result of Coulombic repulsions between the negatively charged N atoms.…”