Phosphindolizine: a compound with planar phosphorus

Abstract

Phosphindolizine, a fused ring with a bridgehead tricoordinated phosphorus, is nearly planar, with an inversion barrier of 3.5 kcal mol^-1 at the B3LYP/6-311+G** level of theory. Diphosphaphosphindolizine is planar. Both the six- and the five-membered rings exhibit significant aromatic character, even in phosphindolizine, which is not entirely planar. The lone pair of the tricoordinate phosphorus is delocalized. The estimated aromatic stabilization in the two rings is 40 kcal mol^-1.