Iodine iodonium salt complexes

Reaction between di-iodine and thioamides such as BZIM (5) or TZD (6) leads to the formation of iodonium salt complexes of [ (TZBl Rj-Ij 21 ] (23) and [(BZIM) [(BZIM)l2] (24) formulae according to the reaction in Scheme 13.1 [10],... 

It has also been shown that the disproportionation reaction, with the generation of the ionic componnd from thioamide-iodine complexes, exhibits pressure dependence [2]. A pressnre increase, leads to the ionic iodonium salt (iii) from (ii) (Scheme 13.2). The favouring of [MBZIM) ] [I3] (24a) formation, is also proven by compntational stndies, based on energetic gronnds [6]. 

Vinyliodonium ions, 35 and 36, are hypervalent iodine species in which one or two alkenyl ligands are bound to a positively charged iodine(III) atom. Although they are reactive with nucleophilic reagents, they are less labile than alkynyliodonium ions, and stable halide salts of vinyliodonium ions can be prepared. The first vinyliodonium compounds [i.e. (a, / -dichlorovinyl)iodonium salts] were synthesized by the treatment of silver acetylide-silver chloride complexes with (dichloroiodo)arenes or l-(dichloroiodo)-2-chloroethene in the presence of water (equation 152). The early work was summarized by Willgerodt in 1914115. This is, of course, a limited and rather impractical synthetic method, and some time elapsed before the chemistry of vinyliodonium salts was developed. Contemporary synthetic approaches to vinyliodonium compounds include the treatment of (1) vinylsilanes and vinylstannanes with 23-iodanes, (2) terminal alkynes with x3-iodanes, (3) alkynyliodonium salts with nucleophilic reagents and (4) alkynyliodonium salts with dienes. 

Benzene formed from photolysis of the 1 1 complex is a cage-escape product from 3(Jul-CHO+ /Ph ). Benzene formed from the photolysis of the 2 1 complex is an in-cage product from 3((Jul-CHO)2 /Ph ). The formation of 2 1 complexes of amino-substituted ketones and iodonium salts has been suggested to account for the high photosensitivity of polymeric Mannich bases with iodonium salts [102]. Formation of 2 1 donor iodonium cation complexes has been rationalized by consideration of the crystal structures of diphenyliodonium halides, which crystallize as dimers with square planar iodine atoms with two bridging halide counterions [102,108]. 

When di-iodine reacts with heterocycles like thioamides or selonoamides new charge transfer complexes containing iodine are obtained [1-10], Various types of such complexes have been obtained thus far, including so called spoke or extended spoke structures (DS 1 or DS l -1 ) (D is the hgand donor) [1], Also iodine coordinated to two thioamides to form iodonium salts ([DS-I-DS] (Ij) )... 

A detailed mechanism of the process shown in Scheme 1.3 is unknown. Two general mechanistic pathways, dissociative and associative, have been proposed for the ligand exchange reactions of X -iodanes (Scheme 1.4) [26, 127]. The dissociative pathway seems to be less likely to occur, because of the low stability of the dico-ordinated iodonium ion [PhIL]+ involved in this mechanism [127]. Such iodonium 8-1-2 species, however, have been frequently observed in the gas phase, for example, in mass spectrometry studies of protonated iodosylbenzene, [PhIOH]+ [101], or in the mass spectra of all known iodonium salts, [ArIR]+. The presence of cationic iodonium species in aqueous solution has been confirmed by spectroscopic measurements and potentiometric titrations of PhI(OH)OTs and PhI(OH)OMs [198] however, all available experimental data show that the iodonium species in solution are coordinated with solvent molecules or with available counteranions. X-Ray diffraction analysis of the protonated iodosylbenzene aqua complexes [PhI(H20)0H]+ isolated from aqueous solutions revealed a T-shaped stmcture, ligated with one water molecule at the apical site of the iodine(III) atom of hydroxy(phenyl)iodonium ion, with a near-linear O-I-O triad (173.96°), which is in agreement with a regular X -iodane structure [178]. 

Single-crystal X-ray structures have been reported for the following aryl- and heteroaryliodo-nium salts diphenyliodonium triiodide [412], (2-methylphenyl)(2-methoxyphenyl)iodonium chloride [413], (2-methoxy-5-methylphenyl)(4-methoxy-2-methylphenyl)iodonium trifluoroacetate [414], (2-methoxy-5-methylphenyl)(4-methoxyphenyl)iodonium trifluoroacetate [415], a complex of diphenyliodonium tetrafluoroborate with pyridine [416], a complex of diphenyliodonium tetrafluoroborate with 1,10-phenanthroline [417], a complex of diphenyliodonium tetrafluoroborate with 18-crown-6 [418], 1-naphthylphenyliodonium tetrafluoroborate [419], 3,10-dimethyl-10//-dibenzo[, e]iodinium tetrafluoroborate [420], aryl(pentafluorophenyl)iodonium tetrafluoroborates [421], 4,4 -[bis(phenyliodonium)]-diphenylmethane ditriflate [422], [bis(4-methoxyphenyl)](diethylaminocarbodithioato)iodine(in) [423], di(p-tolyl)iodonium bromide [424], diphenyliodonium chloride, bromide and iodide [425,426], diphenyliodonium nitrate [427], diphenyliodonium tetrafluoroborate [428], thienyl(phenyl)iodonium salts [401], (anft-dimethanoanthracenyl)phenyliodonium tosylate and hexafluorophosphate [429] and 3-mesityl-5-phenylisoxazol-4-yl(phenyl)iodonium p-toluenesulfonate [409]. 

Electrophilic iodine reagents are extensively employed in iodocyclization (see Section 4.2.1). Several salts of pyridine complexes with 1+ such as bis-(pyridinium)iodonium tetrafluoroborate and b/.s-(collidine)iodonium hexafluorophos-... 

Electrophilic iodine reagents have also been employed in iodocyclization. Several salts of pyridine complexes with I+ such as bis(pyiidinium)iodonium tetrafluoroborate and bis(collidine)iodonium hexafluorophosphate have proven especially effective.61 y-Hydroxy- and d-hydroxyalkcncs can be cyclized to tetrahydrofuran and tetrahydropyran derivatives, respectively, by positive halogen reagents.62 (see entries 6 and 8 in Scheme... 

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