Darstellung und Konformationsuntersuchungen von cis- und trans-Isomeren des 1,2,4,5-Tetramethyl-3,6-diphenoxy-3,6-dithioxo-1,2,4,5-tetraaza-3,6-diphosphacyclohexans

Synthesis and Conformational Analysis of Cis- and Trans-Isomers of 1,2,4,5-Tetramethyl-3,6-diphenoxy-3,6-dithioxo-1,2,4,5-tetraaza-3,6-diphosphacyclohexane A mixture of isomers of the title compound could be prepared in much better yields (up to ca. 25%) by the reaction of bis(1,2-dimethylhydrazido) thiophosphoric acid O-phenylester with phenoxythiophosphoryl dichloride in the presence of triethylamine and aluminum chloride as catalyst. Separation of cis- and trans-isomers was achieved by sorting of crystals or in low yields by fractional crystallization. ³¹P- and mainly ¹H-NMR investigations at different temperatures show, that in both isomers the saturated sixmembered ring has a twist-conformation in which sulfur and phenoxy substituents located cis or trans respectively adopt the isoclinal positions. The isomers reveal remarkably different barriers of activation for the interconversion of two enantiomeric twist forms (cis ΔG^# = 63 ± 1 kJ/mol; trans 47 ± 1 kJ/mol).