Polar Radicals. 17. On the Mechanism of Iodine Atom Transfer. A 9-I-2 Intermediate

Article abstract of DOI:10.1021/ja00378a022

The atom-transfer reaction of iodine from an aryl iodide to a phenyl radical has been shown to proceed via a 9-I-2 ntermediate.The relative kinetics of the reactions of the intermediate were investigated by studying its mode of decomposition upon formation from the reduction of a series of unsymmetrically substituted diaryliodonium salts.The iodonium salts were reduced by the electron-transfer reactions with several reagents: di-tert-butyl nitroxide, sodium 2,6-di-tert-butylphenylate, and sodium phenylate.The reduction by electron transfer of the iodonium salts by the latter reaction gives high yields of diaryl ethers.The mechanism fo ether formation has been shown to proceed by two mechanistic pathways.For the diaryliodonium salts that have a p-cyano or p-nitro substituent, the ether is formed by a nucleophilic aromatic substitution; however, when the substituents were not strongly electron withdrawing, the mechanism resulting in ether formation involved electron transfer from the phenylate anion to the iodonium salt to form the phenoxy radical and a 9-I-2 intermediate.The intermediate decomposes to an aryl radical and an aryl iodide.The ether is formed from the efficient coupling of the aryl radical and the phenoxy radical.