Sulphur–nitrogen anions: 14N and 15N NMR investigations of the deprotonation of cyclic sulphur imides and sulphur–ammonia solutions

Abstract

The following systems have been investigated by 14N and (or)15N NMR spectroscopy: (a) the deprotonation of S7NH by n-BuLi, (b) solutions of S8, S7NH, 1,3- and 1,4-S6(NH)2, and K2SN2 in liquid ammonia, (c) the reaction of sodium azide with sulphur in hexamethylphosphoramide (HMPA), (d) the reactions of S7NH and S4(NH)4 with potassium amide in liquid ammonia in various molar ratios, and (e) the reaction of (NSCl)3 with potassium amide (1:6 molar ratio) in liquid ammonia. These investigations have provided an NMR characterization of the thermally unstable S7N− (δ15N ca. −324 ppm) and S2N2H− ions (δ14N + 7 and −149 ppm, 1J(14N−1H) 36 Hz, 1J(15N−H) 55 Hz, 2J(15N-15N) 2.2 Hz) in liquid ammonia, demonstrated the existence of S7N−, in addition to SSNSS−, as the major nitrogen-containing ingredient of sulphur–ammonia solutions (SAS), and confirmed the formation of the SSNSS−, but not S7N−, from the reaction of sodium azide and sulphur in HMPA. Consistent with previous chemical investigations, the NMR data show that the S7N− and S2N2H− ions are thermally unstable with respect to the formation of SSNSS− and S3N3−, respectively, in solution. Solutions of S4(NH)4/4KNH2 or (NSCl)3/6KNH2 show the same two 14N or 15N NMR resonances at ca. +97 and −108 ppm as a solution of NSN2− in liquid ammonia. Keywords: sulphur–nitrogen anions, nitrogen NMR, liquid ammonia.