The cycloaddition reaction of 1,3-diphospha-2,4,5-tri-t-butylcyclopentadiene and 1,2,4-triphospha-3,5-di-t-butylcyclopentadiene: crystal and molecular structure of the ethanol adduct of P5C5But5H2

Abstract

Protonation of a 1 : 1 mixture of the anions (P₂C₃Bu^t₃)^–, 1 and (P₃C₂Bu^t₂)^–, 2, affords the corresponding di- and tri-phosphacyclopentadienes 3 and 4 which undergo a [4 + 2] cycloaddition reaction to form P₅C₅Bu^t₅H₂5 whose structure has been elucidated by NMR spectroscopy and a single crystal X-ray study of its EtOH adduct P₅C₅Bu^t₅H₃(OEt), 6; in the [4 + 2] cycloaddition reaction the diphosphacyclopentadiene acts as the diene and the triphosphacyclopentadiene as the dieneophile, unlike the corresponding self-cycloaddition reaction of the triphosphacyclopentadiene there is no subsequent [2 + 2] cycloaddition of the CC and PC bonds in 5 to give a cage structure.