Synthesis, Characterization, X-Ray Structural Analysis, and Iodination Ability of Benzyl(triphenyl)phosphonium Dichloroiodate

Benzyl(triphenyl)phosphonium dichloroiodate (BTPPICl₂), BnPh₃P⁺(ICl₂)⁻, is easily synthesized in a nearly quantitative yield by the addition of BnPh₃P⁺Cl⁻ to a CH₂Cl₂ solution of iodine monochloride (ICl). BnPh₃P⁺Cl⁻ can be prepared by the reaction of Ph₃P and BnCl. The compound was characterized by physicochemical and spectroscopic methods (elemental analysis, FT-IR, and ¹H-NMR). The use of phosphonium counterion improves the quality of the BTPPICl₂ crystals. BTPPICl₂ crystallizes in the monoclinic system, and its crystal and molecular structure has been determined at 100(1) K by X-ray diffraction. The structure was solved by the direct method and had refined R value of 0.0637 for 699 reflections (I>2σ(I)), space group P21/n with a=12.4700(3), b=13.2196(3), c=14.4580(3) Å, β=102.6340(10)°, V=2325.67(9) ų, and Z=4. The I-atom is coordinated by two Cl-atoms as ligands in a linear geometry. This compound is a versatile reagent for the efficient and selective iodination of organic substrates, in particular of aromatic phenols to the corresponding iodo compounds, under mild conditions. To assess the generality of method, a wide variety of phenols with electron-donating and electron-withdrawing substituents were studied. BTPPICl₂ is a mild iodination reagent, which offers a new avenue for an expeditious iodination of phenols. The inexpensive, relatively non-toxic reagent, and mild conditions are the positive features of the procedure and reagent.