1.2- Difluoro-4-iodobenzene

It was later discovered that the reactive intermediates in the iron porphyrin model systems were high-valent oxoiron porphyrin complexes. A green oxoiron(IV) porphyrin cation radical species (13) has been well characterized by various spectroscopic techniques, including visible spectroscopy, NMR, EPR, Mossbauer, and EXAFS (Figure 1.11) . It has recently been shown by Nam and Que that the oxygen-atom transfer from certain iodosylarenes is reversible with some iron porphyrins. For the case of 1,2-difluoro-4-iodobenzene both an oxoferryl species and an iodosyl-ferric species were observed to be in equilibrium . 

To overcome problems associated with the removal of iodobenzene and its derivatives formed upon fluorination of arylalkenes and arylalkynes with (difluoroiodo)arenes, polymer-supported (difluoroiodo)arenes were proposed.139 With these agents, the separation procedures are reduced to filtration of the iodinated polymer. For this purpose popcorn polystyrene is io-dinated and then transformed into the difluoroiodide by treatment with xenon difluoride in the presence of hydrogen fluoride in dichloromelhane at 25 C. The amount of active fluorine bonded to iodine atoms on the polymer support is estimated by iodometric titration. The reactions with phenyl-substituted alkenes result in rearranged gew-difluorides. The procedure provides the same fluorination products as with (difluoroiodo)benzenc (see Section 4.13.) but in much higher yields, e.g. PhCF2CH2Ph (96%), PhCF2CH(Me)Ph (95%). PhCH2CF2H (86%), and l,l-difluoro-2-phenylcyclopentanc (91 %). 

The following give abnormal results when treated with chlorosulphonic acid alone, preferably at 50 °C for 30-60 minutes fluorobenzene (4,4 -difluoro-diphenylsulphone, m.p. 98 °C) iodobenzene (4,4 -diiododiphenylsulphone, m.p. 202 °C) o-dichlorobenzene (3,4,3, 4 -tetrachlorodiphenylsulphone, m.p. 176 °C) and o-dibromobenzene (3,4,3, 4 -tetrabromodiphenylsulphone, m.p. 176— 177 °C). The resulting sulphones may be crystallised from glacial acetic acid, toluene or ethanol, and are satisfactory for identification of the original aryl halide. In some cases sulphones accompany the sulphonyl chloride they are readily separated from the final sulphonamide by their insolubility in cold 6 m sodium hydroxide solution the sulphonamides dissolve readily and are reprecipitated by 6 m hydrochloric acid. 

To investigate the mechanism further, a series of intramolecular competitive leactions of (difluoro)(phenyl)(4-substituted phenyl)silanes with iodobenzene were performed. As may... 

Direct anodic oxidation of iodobenzene and /Mira-methyliodoben-zene did not give the corresponding hypervalent difluorides. Therefore, indirect anodic oxidation was attempted using a chloride ion mediator. In this case, the desired difluoro products are not formed but instead a novel hypervalent iodobenzene derivative, such as 73, having I-F and I-Cl bonds is produced. It was found that difluorina-tion occurs by the reaction of dithioacetals with iodobenzene chlo-rofluorides. Indirect anodic oxidation of dithioacetals by using a catalytic amount of para-methoxyiodobenzene was attempted as shown in Scheme 55 and it was found that desulfurizative difluorina-... 

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