Iodoarenes tetrafluoroborate

Comparisons of product distributions in thermal and photochemical solvolyses show that the primary vinyl cation is not involved in thermolysis but is formed photochemically. The chirality probe approach using optically active 4-methylcyclohexylidenmethyl(aryl)iodonium tetrafluoroborate 19 was applied to the photosolvolysis.24 The rearranged product 4-methylcycloheptanone retained some optical activity, but the enantiomeric product in slight excess has a different structure depending on the iodoarene leaving group Arl of the substrate. The results indicate that the primary vinyl cation involved is not in a free, dissociated achiral form. 

Oxidation of iodoarenes was also effective with NaB03 H20 in Ac20/H2S04. The bromides were converted into the more useful ionic nitrates, trifluoroac-etates or tetrafluoroborates by oxidative anion metathesis, using the corresponding acid and 30% hydrogen peroxide, and refluxing the mixtures in methanol any liberated bromine was trapped by cyclohexene [20]. 

In this context, a functionalized ionic liquid, 1-(2-hydroxyethyl)-3-methyl imidazolium tetrafluoroborate [hemim][BF4], is reported as an efficient and recyclable reaction medium for the palladium catalyzed Heck reaction. The olefination of iodoarenes and bromoarenes with olefins generates the corresponding products in good to excellent yields under phosphine-ffee reaction conditions. After separation of the product, fresh starting materials are charged into the recovered ionic liquid which entraps the palladium catalyst. The reactions still proceed quantitatively for six cycles, without significant loss of catalytic activity. " The effect of both the cation and the anion on the chemical yield is shown in Figure 28. 

Hypervalent iodine reagents. Co-oxidation of electron-rich iodoarenes and iodine leads to diaryUodonium species which are conveniently isolated as tosylate or triflate salts/ For access to an unsymmetrical diaryhondium salt the oxidation is carried out with a mixture of a Art and Ar B(OH)2, in the presence of BF3 OEt2 (to form a tetrafluoroborate salt) at room temperature/... 

The mechanism of solvolysis of methoxy-substituted diaryliodonium tetrafluoroborates, Arl+Ph Bp4, in methanoi and 2,2,2-trifluoroethanol has been investigated [893]. The solvolysis products include alkox-ide substitution products (ArOR and PhOR) as well as iodoarenes (Phi and Arl). The ratios of products, ArOR/PhOR, range from 8 2 to 4 6. The results of this study provide experimental evidence against the formation of aryl cation under these conditions and support the pathways via ligand coupling or 5nAt2 mechanisms involving a solvent molecule as a nucleophile in the transition state [893]. If the reaction is performed in inert (not nucleophilic) solvent, various nucleophiles may be involved in the reaction with iodonium salt. 

Arenediazonium tetrafluoroborates (ArN2Bp4 where Ar=X-C6H4 X=H, 2-Me, 3-Me, 4-Me, 4-MeO, 4-MeCO, 2-Ph, 2-CI, 3-CI, 4-CI, 4-Br, 4-1, 3-NO2 and 4-NO2), like iodoarenes are converted into aldehydes in good yield by palladium-catalyzed carbonylation in the presence of poly-methylhydrosiloxane (PMHS) at room temperature. The rather slow reaction rate is remarkably enhanced by replacing the polymeric silane with EtaSiH (Eq 1.37). ° ... 

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