Electron transfer from a cyclic diaryliodine species to arenediazonium salts. Evidence for the intermediacy of 9-I-2 structures in iodine atom transfer reactions

2,2'-Diiodobiphenyl (1) reacts with arenediazonium hexafluorophosphates (ArN2+PF6-) in acetonitrile to form biphenyleneiodonium salt (4) and iodoarenes (ArI) as major products. The reaction follows a free-radical-chain mechanism and involves a cyclic diaryliodine, 9-I-2 species (3), which is trapped as the iodonium salt (4) by a single-electron transfer (SET) to the diazonium salt. The results show that diaryliodine intermediates formed by the addition of phenyl radicals to iodoarenes can have sufficient lifetimes to allow trapping by bimolecular processes.