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

Abstract

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 New Class of Two‐Deck Dicationic Heteropentalenes Existing by the Balance between Interdeck Aromaticity and Covalent P−P Bonding

“…31 P{ 1 H} (162 MHz, CD 3 CN, 293 K): δ = 108.9 ppm (s). 19 (cHexDDP) 2 (OTf) 2 (4). An equimolar mixture of cHexDDP (250 mg, 1.0 mmol) and cHexDDPCl2 (321 mg, 1.0 mmol) (Scheme 3) in methylene chloride (20 mL) was kept for 1 h at room temperature, and then 444 mg (2.0 mmol) TMSOTf was added.…”

“…Their important feature is that these compounds, unlike related aromatic P-containing heterocycles (azaphospholes, diazaphospholes, phosphinines), are π-donor heterocycles capable of forming charge-transfer complexes with organic π-acceptors. [18,19] The reason for such a striking difference is the high energy of the HOMO of diazadiphosphapentalenes localized on the π-system. A characteristic feature of DDPs is the dualism of their electronic structure, which makes it possible to consider them both as heterocycles and as stabilized (masked) singlet phosphinidenes [20] (Scheme 2).…”

“…The basis of two‐deck dications is 3a,6a‐diaza‐1,4‐diphosphapentalenes which can also be attributed to the young class of compounds. Their important feature is that these compounds, unlike related aromatic P‐containing heterocycles (azaphospholes, diazaphospholes, phosphinines), are π‐donor heterocycles capable of forming charge‐transfer complexes with organic π‐acceptors [18,19] . The reason for such a striking difference is the high energy of the HOMO of diazadiphosphapentalenes localized on the π‐system.…”