SYNTHESIS, PROPERTIES, AND REACTIVITY OF N,N'-DIFLUOROBIPYRIDINIUM AND RELATED SALTS AND THEIR APPLICATIONS AS REACTIVE AND EASY-TO-HANDLE ELECTROPHILIC FLUORINATING AGENTS WITH HIGH EFFECTIVE FLUORINE CONTENT

N,N'-Difluoro-2,2'-, -2,4'-, -3,3'-, -4,4'-bipyridinium and substitute d N,N'-difluoro-2,2'-bipyridinium bis(triflates), bis(tetrafluoroborat es), bis(hexafluorophosphates), and bis(hexafluoroantimonates) 1-9 wer e synthesized in high yields by the direct fluorination of a mixture o f a bipyridyl and a Lewis acid, a Bronsted acid, or the alkali metal s alt of an acid. The higher homologues, trimer 10 and polymer II, were also synthesized. Unsubstituted or electron-donating group-substituted N,N'-difluorobipyridinium salts are stable nonhygroscopic crystals, w hile the electron-withdrawing group-substituted N,N'-diflurobipyridini um salts 3, 5, and 6 are moisture-sensitive crystals. Hydrolysis of Ib in boiling water gave 3,3'-dihydroxy-2,2'-bipyridyl. The reactivity d etermination indicated that the fluorinating capability decreased in t he order 2,2'- much greater than 2,4' > 3,3'- approximate to 4,4'-isom er much greater than N-fluoropyridinium salt and that the two N-F moie ties in a molecule mere effective for fluorination. This fluorination occurred in a step-by-step manner, and the reactivity difference betwe en the first and second fluorinations was very small. N,N'-Difluoro-2, 2'-bipyridinium bis(tetrafluoroborate) (Ib) is thus shown to be a high ly reactive and easy-to-handle electrophilic fluorinating agent with t he high effective fluorine content (103.3 g/kg) for preparing many flu oro organic compounds.