Reactions of fluoroalk-1-en-1-yltrifluoroborate and perfluoroalk-1-yn-1-yltrifluoroborate salts and selected hydrocarbon analogues with hydrogen fluoride and with halogenating agents in aHF and in basic solvents

The relative rate of the electrophilic hydrodeboration of K[R′BF3] with HF (27–100%) diminishes in the series R′ = C4H9CC > C4F9CFCFCC > CF2C(CF3) > C3F7CC ∼ (CF3)2CFCC > CF3CC. When R′ = CF3CC the new salt K[CF3CH2–CF2BF3] was obtained by addition of HF besides CF3CCH and K[BF4]. Small amounts of water caused the formation of K[CF3CH2–C(O)BF3] as a by-product. The electrophilic halofluorination of perfluoroalkenyltrifluoroborate salts with NCS or NBS in aHF (anhydrous HF) led to K[RFCFHal–CF2BF3] (from K[RFCFCFBF3]) and K[RFCHal2–CF2BF3] (from K[RFCHalCFBF3] and K[RFCCBF3]) (Hal = Cl, Br). Treatment of K[RFCFCFBF3] and K[RFCCBF3] with 5% F2/N2 in MeCN gave the corresponding salts K[RFCF2–CF2BF3] in 16–25% isolated yield. Reactions of K[trans-C4F9CFCFBF3] with Cl2 in MeOH resulted in K[C4F9CFCl–C(O)BF3] (major product). The latter was also obtained in reactions of K[trans-C4F9CFCFBF3] with Cl2 in MeCN or sulfolane after sequential methanolysis of the primarily formed products. In contrast, the salts K[RCFCFBF3] (R = CnF2n+1, trans-C4H9) and K[CF3CCBF3] underwent bromodeboration to RCFCFBr and CF3CCBr, respectively, when they were reacted with bromine in the polar solvents MeOH, MeCN, or sulfolane.

The electrophilic halofluorination of K[RFCFCFBF3] and K[RFCHalCFBF3] or K[RFCCBF3] with NCS or NBS in aHF yielded K[RFCFHal–CF2BF3] and K[RFCHal2–CF2BF3] (Hal = Cl, Br), respectively. K[CF3CCBF3] in aHF solution added slowly HF and formed K[CF3CH2−CF2BF3] besides protodeboration (CF3CCH and K[BF4]). In the presence of traces of water K[CF3CH2−C(O)BF3] was obtained as a by-product. K[trans-C4F9CFCFBF3] reacted with Cl2 in MeOH to give K[C4F9CFCl−C(O)BF3].Figure optionsDownload as PowerPoint slideHighlights
► Electrophiles react with fluorinated alk-1-en-1-yl- and alk-1-yn-1-yltrifluoroborates.
► H+ and “Hal+” attack C2 of C–C multiple bonds in alkenyl- and alkynyltrifluoroborates.
► H–F and “Hal–F” addition contra hydro- and halodeboration (C–B bond splitting).
► Electrophilic halofluorination with NCS and NBS in alkenyl- and alkynylfluoroborates.
► Fluorination of alkenyl- and alkynyltrifluoroborates with elemental fluorine in MeCN.