3a,6a‐Diaza‐1,4‐diphosphapentalenes: Synthesis and Complexation with the Organic π‐Acceptor 1,2,4,5‐Tetracyanobenzene

The reaction of PCl₃ 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 (Csp²−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.