Diphosphonio Isophosphindoles, Phospholes with a Planar Phosphorus

Which resonance formula is correct? The protonation of 1 to the symmetrical dication 2 is certainly most plausible from the indicated phosholide structure, which confers distinct basic character on the ring phosphorus. The bonding of the system 2 stable at room temperature, a phosphole with PH group, is however best explained by the phosphorane structure 2b. Certain is, that the reactivity and stability of these systems are understandable only in terms of the interplay of phosphonio substituents and annelated benzene ring.