15N NMR study of dialkyl, N‐alkyl‐N′‐phenyl and diphenyl sulphur diimides: Assignment of configuration in solution

Abstract

¹⁵N NMR spectra of dialkyl sulphur diimides (1) [R¹(NSN)R²; R¹ = R² = Me (a), Et (b), ⁿPr (c), ⁱPr (d), ⁿBu (e), ^tBu (f), ^tOct (g)], N‐alkyl‐N′‐phenyl sulphur diimides (2) [R¹(NSN)R²; R¹ = Me (a), Et (b); R² = Ph] and diphenyl sulphur diimide (3) were measured at variable temperature. The assignment is based on the comparison with data for the corresponding N‐sulphinylamines R¹(NSO). The Z/E configuration is always preferred at low temperature, whereas the minor isomer adopts the Z/Z configuration. In the presence of bulky substituents (If and g), only the isomer with Z/E configuration is observed. At room temperature, ¹⁵N NMR signals were not observed for symmetrically substituted sulphur diimides, but a single averaged ¹⁴N resonance can be measured. The unsymmetrically substituted sulphur diimides 2a and b adopt the Z/E configuration with the alkyl group Z and the phenyl group E. There are no indications of other isomers at low temperature. ¹⁴N NMR spectra at room temperature prove that the (Z)‐phenyl/(E)‐alkyl isomer contributes little to the equilibrium.