Cationic Diiodo-Phosphoranides through Oxidative I-2 Addition to Tricyclic Phosphamethine Cyanines

Reaction of methylene- and ethylene-bridged bis-imidazolium salts with white phosphorus in the presence of KOtBu furnished moderate yields of tricyclic bis-imidazolio-phosphanide halides. Further oxidation of the products with one equivalent of I-2 gave bis-imidazolio-diiodophosphoranide iodides. All newly prepared compounds were characterized by analytical and spectroscopic data and single-crystal XRD studies. DFT calculations provide evidence for substantial stabilization of cyclic bis-imidazolio-phosphanide cations by pi-conjugation effects and suggest describing the bis-imidazolio-diiodophosphoranide cations as charge-transfer complexes of dicationic iodophosphines with iodide.