Sulfur diimides of the type R(NSN)R' (1-19, 2a-9a, 12a-17a, 20a, 3b-16b, 20b) were investigated by N-15, Si-29 and Sn-119 NMR at variable temperature in order to determine their preferred configuration (E/Z, Z/E, E/E or 2/2) in solution. All sulfur diimides studied are highly fluxional at room temperature. In some cases with N(t)Bu groups, the presence of two isomers could be demonstrated. In solution, the E position is preferred for a silyl group, as shown, e.g., for N-tert-butyl-N'-trimethylsilyl sulfur diimide (2a). In the case of one germyl group, there is little preference of either E or Z position, whereas stannyl groups prefer to be in Z position. The situation in solution may differ considerably from the configurations determined in the solid state. Single crystal X-ray analyses were carried out for di-tert-butyl- (1), bis(triphenylsilyl)- (7) and N-trimethylsilyl-N'-triphenylsilylsulfur diimide (7b). All three molecules adopt the Z/E configuration in the crystal. Solid-state Si-29 CP/MAS NMR spectra indicate that in the case of 7 the bulk material consists of two isomers, one with the Z/E configuration, as found from the X-ray analysis, and a second one, most likely with E/E configuration. Solid-state Sn-119 CPIMAS NMR spectra of bis(trimethylstannyl)sulfur diimide (4) prove that there is only one tin site in the solid state, most likely the isomer with Z/Z configuration. In contrast, solid-state Sn-119 NMR spectra of bis(triphenylstannyl)sulfur diimide (6) suggest that it exists solely as isomer with Z/E configuration.
