3 a,6 a-Diaza-1,4-Diphosphapentalenes: Synthesis and Complexation with the Organic π-Acceptor 1,2,4,5-Tetracyanobenzene.

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 -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.