Reported here for the first time are the synthesis and characterization of supramolecular complexes between diaryl-lambda(3)-iodanes and 18-crown-6 (18C6). Slow evaporation of solvents afforded 1:1 and 2:1 complexes between Ph(2)IBF(4) and 18C6 as stable crystals, depending on the conditions. X-ray crystal structures of these complexes indicated that each iodine atom contacts with the three adjacent oxygen atoms of 18C6 through two hypervalent secondary bonding and a weak interaction. (1)H NMR analyses and CSI-MS spectra showed that, in dichloromethane solution, Ph(2)IBF(4) exclusively forms the 1:1 complex with 18C6 (binding constant K(a), 1.02 x 10(3) M(-)(1)). The binding constants decrease with the increased solvent donor ability (Gutmann's DN). Changing the heteroatom ligand from BF(4) to the less nucleophilic PF(6) and AsF(6) increased the binding constant by about six times. Substitution of an electron-withdrawing group onto the para position of Ph(2)IBF(4) tends to increase in the complex stability. A linear Hammett relationship (rho = 0.59) between log K(a) and sigma(p)(+) values of substituents indicates that the diaryl-lambda(3)-iodanes with electropositive iodine(III) interact more efficiently with 18C6. Decreased binding magnitude was measured with 15C5, dibenzo-18C6, dibenzo-21C7, and dibenzo-30C10.
Tetra-n-butylammonium oxido-lambda(3)-iodane, prepared from 1-hydroxy-1,2-benziodoxol-3(1H)-one by reaction with tetra-n-butylammonium fluoride, directly undergoes oxygen atom transfer to alpha,beta-unsaturated carbonyl compounds, yielding epoxides.
The Koser reagent, [hydroxy(tosyloxy)iodo]benzene (1; Ts = p-toluenesulfonyl), is a useful oxidizing agent for a range of organic substrates.[1] It has been reported that upon dissolution in water the l 3 -iodane undergoes complete ionization to give the hydroxy(phenyl)iodonium cation (PhI + OH).[2] The hydroxy(phenyl)iodonium ion does not form an ion pair with a tosylate ion and is presumed to be ligated with at least one water molecule at an apical site of the iodine(iii) center. This aqua(hydroxy)(phenyl)iodonium ion 2 (L = H 2 O) is highly soluble in water with a pK a value of 4.30 at 20 8C.Iodosylbenzene is a polymer bridged by secondary I···O hypervalent interactions, [3] and hence is essentially insoluble in both nonreactive organic solvents and water at near neutral pH conditions; [4] however, at pH < 2.3 iodosylbenzene is highly soluble in water, in which 2 (L = H 2 O) was also assumed to be a primary monomeric species. [2] Aqua complexes of l 3 -iodanes with a water molecule coordinated to an iodine(iii) center are unique, and there are no well-established precedents. Therefore, direct evidence supporting the proposed structure of 2 (L = H 2 O) is highly desirable. Recently, Wirth and co-workers synthesized an interesting chiral hydroxyiodonium ion 3, in which the oxygen atom of the ortho methoxymethyl group replaces the tosylate ligand of the Koser reagent with a near-linear O À I···O triad. [5] We have reported the isolation and characterization of the crown ether complex 2·BF 4 À (L = [18]crown-6) of hydroxy-(phenyl)iodonium ion. In this complex, an oxygen atom of the crown ether is tightly bound to the iodine(iii) center at the apical site and forms a T-shaped structure with linear OÀI···O hypervalent bonding.[6] Herein, we report the first synthesis
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