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(III) 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 cisand 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 infl uence of the donor solvent, which was confi rmed by 31 P NMR spectroscopy, electronic absorption spectroscopy, and independent syntheses.

The reaction of PCl 3 with diethyl ketazine and 4-phenylcyclohexanone azine results in the formation of 1,4-dichloro-3a,6a-diaza-1,4-diphosphapentalenes which were reduced by magnesium in THF to give corresponding diazadiphosphapentalenes EtMeDDP and PhcHexDDP, containing two-coordinate phosphorus atoms. According to the CVA data, the new diazadiphosphapentalenes are strong electron donors showing oxidation peak potentials at 0.34 and 0.10 V, respectively, (vs. Ag/AgCl). Interaction of 1,2,4,5-tetracyanobenzene (TCNB) with the obtained diazadiphosphapentalenes in any stoichiometry produces sandwich complexes of the composition DDP-TCNB-DDP. Black-purple crystals of π-complexes contain infinite molecular chains with short P•••P contacts between DDP molecules and short (Csp 2 À H•••N) contacts between TCNB molecules. Calculations showed that each TCNB molecule is an acceptor of ~0.3e from two DDP molecules. Estimation of the HOMO-LUMO gap from the onset of optical absorption give values of 1.25 eV and 1.31 eV for [(EtMeDDP) 2 (TCNB)] and [(PhcHexDDP) 2 (TCNB)] respectively.

A number of two‐deck dicationic 3a,6a‐diaza‐1,4‐diphosphapentalenes (DDP)2X2 (X=halogen or complex ion) have been characterized. Interdeck distances P(1)⋅⋅⋅P(3) and P(2)⋅⋅⋅P(4) in crystal structures, as a rule, significantly exceed the sum of covalent radii, however they are still within the sum of van der Waals radii. The 31P NMR data indicate that phosphorus atoms are equivalent in solution even at low temperatures (233 K). Based on DFT calculations, the formation of two equivalent P−P covalent bonds (<2.4 Å) is energetically unfavorable, despite the absence of steric barriers. The total energy of the model dication as a function of the P⋅⋅⋅P separation has a minimum at the P−P distance of 2.85 Å. This distance corresponds to the highest aromaticity index in the interdeck space (NICS(1.0)=−20.72). The energy of interdeck interactions is estimated at 10–15 kcal/mol.

No abstract

No abstract