Synthesis of 3a,6a-diaza-1,4-diphosphapentalenes and their halogen derivatives. Specific features of the structure and behavior in solutions

Such ketazines as azines of acetophenone and its substituted derivatives (p-F, m-Cl, p-I, p-Me, p-OMe), acetone, dibenzyl ketone, propiophenone, and indan-2-one were studied in the reaction with phosphorus(ɪɪɪ) chloride. The possibility of the formation of 1,4-dichloro-3a,6a-diaza-1,4-diphosphapentalenes is largely determined by the nature of the starting ketazine. Diazadiphosphapentalene dichlorides exist in solution as a mixture of cis- and trans-isomers, but crystallize exclusively as 1,4-trans-isomers. Reduction of 3a,6a-diaza-1,4-diphosphapentalene dichlorides with manganese in tetrahydrofuran gives the corresponding diazadiphosphapentalenes in 52–63% yield. The electrochemical properties of the obtained compounds were studied by cyclic voltammetry. Two dichlorides of 3a,6a-diaza-1,4-diphosphapentalenes were found to have anomalous oxidation potentials of 0.29 and 0.13 V related to the formation of free diazadiphosphapentalenes in solution as a result of disproportionation under the influence of the donor solvent, which was confirmed by 31P NMR spectroscopy, electronic absorption spectroscopy, and independent syntheses.