Polycoordinated iodine compounds

The triple bond of alkynes constitutes one of the oldest, simplest and most valuable functional groups in organic chemistry. Besides the common hydrocarbon acetylenes, a wide variety of functionalized alkynes (1) are known that play an important role in numerous organic transformations. The latest members of the family of functionalized alkynes are the alkynyl iodonium salts (2). These compounds are a subgroup of the di-coordinated positively-charged 8-1-2 iodine species L2U (3)k The first example of this type of molecules (4) was initially reported exactly one hundred years ago in 1894 by the German chemists Hartman and Meyer. To date, the best known and most widely used members of this class of polycoordinated iodine compounds are the diaryliodonium salts... 

Iodine differs in many aspects from the other halogens. Because of the large atomic size and the relatively low ionization energy, it can easily form stable polycoordinate, multivalent compounds. Interest in polyvalent organic iodine compounds arises from several factors (a) the similarity of the chemical properties and reactivity of I(III) species to those of Hg(+2), Tl(+3), and Pb(+4), but without the toxic and environmental problems of these heavy metal congeners ... 

Varvoglis, A., The Organic Chemistry of Polycoordinated Iodine,VCH Publishers, New York, 1992. Prakash, O. and Singh, S.P., lodobenzene diacetate and related hypervalent iodine reagents in the synthesis of heterocychc compounds, Aldrichimica Acta, 27,15, 1994. 

The 127I NQR spectra of an extensive series of iodonium compounds, [R2I]+BF, have been reported52,53. In addition to the fact that iodine is the only halogen that forms an extensive series of halonium compounds, the study of 127I has the advantage that, since its spin is equal to 5/2, there are two transitions and therefore both the coupling constant and the asymmetry parameter may be obtained. This is particularly important for a polycoordinated nucleus, since we may anticipate that the asymmetry parameter will be far from negligible. A selection of the NQR parameters for these compounds is shown in Table 9. Also studied were the iodonium halides, whose structures differ from those of the... 

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