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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.

N-Heterocyclic carbene adducts of aluminium triiodide, IMes·AlI3 (1) and IPr·AlI3 (2) (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene and IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) are reported. These adducts are available by the reaction of aluminium triiodide with the correspondingN-heterocyclic carbene. Compounds 1 and 2 are soluble in hydrocarbon solvents, stable in inert atmosphere, and have been characterised by elemental analysis, NMR spectroscopy and single-crystal X-ray diffraction studies.