Hexaphosphabenzene

Hexaphosphabenzene is a valence isoelectronic analogue of benzene and is expected to have a similar planar structure due to resonance stabilization. Although several other allotropes of phosphorus are stable, no evidence for the existence of P₆ has been reported. Preliminary ab initio calculations on the trimerisation of P₂ leading to the formation of the cyclic P₆ were performed, and it was predicted that hexaphosphabenzene would decompose to free P₂ with an energy barrier of 13−15.4 kcal mol⁻¹, and would therefore not be observed in the uncomplexed state under normal experimental conditions. The presence of an added solvent, such as ethanol, might lead to the formation of intermolecular hydrogen bonds which may block the destabilizing interaction between phosphorus lone pairs and consequently stabilize P₆. The moderate barrier suggests that hexaphosphabenzene could be synthesized from a [2+2+2] cycloaddition of three P₂ molecules. Currently, this is a synthetic endeavour which remains to be conquered.