Reactions between N,N'-di-tert-butyl sulfur diimide, (t)Bu(NSN)(t)Bu (1), and the amino-imino-thiophosphoranes Me(3)Si(R)NP(S)=N(t)Bu [R = (t)Bu (6a), SiMe(3), (6b)] afforded the 1,2,4,3-thiadiazaphosphetidines 7a,b via [2 + 2]cycloaddition. The corresponding products 8a,b were obtained when one (t)Bu group in 1 was replaced by a 2-(1,3-di-tert-butyl-1,3,2-diazaphosphoridnyl) group (2). In contrast, the reactions between 6a and the three different 2-(1,3-di-tert-butyl-1,3,2-diazaphospholidinyl)-substituted sulfur diimides [CH2(N(t)Bu)]P-2(NSN)R(1) [R(1) = (t)Bu (3), Me(3)Si (4), [CH2(N(t)Bu)]P-2 (5)1 gave the same phosphorus compound 9 which was identified as a zwitterionic bicyclic amino-imino-thiophosphorane. Exchange between imino groups at phosphorus and sulfur is the first step in this reaction, followed by 1,3-shifts of Me(3)Si and phosphinyl groups and the final intramolecular N-P coordinative stabilization. The products were characterized by nultinuclear NMR (H-1-, C-13- N-15-, Si-29- and P-31 NMR). The molecular structures of the cycloadduct 8a and the zwitterionic compound 9 were determined by single crystal X-ray analyses. In solution, NMR spectra show that 8a is present as a single isomer in solution, whereas NMR spectra of 9 at 218 K indicate the presence of two isomers (86:14).
