Synthesis of K[4-ROC6F4BF3] from potassium pentafluorophenyltrifluoroborate and O-nucleophiles

A new route to potassium polyfluoroaryltrifluoroborates, K[4-ROC6F4BF3], consisting in the nucleophilic alkoxydefluorination of K[C6F5BF3] with MOR (M = K, Na) in a polar aprotic solvent is suggested. Reaction of K[C6F5BF3] with KO-t-Bu proceeds smoothly at 25 °C in DME, but the attempted alkoxydefluorination of K[C6F5BF3] with other NaOR at 30 °C in DME failed. A series of K[4-ROC6F4BF3] (R = Me, Et, Pr, i-Pr, Bu, PhCH2) is prepared using the corresponding sodium alkoxides in DMF at 130 °C in 80–90% isolated yield. Salt K[4-CH2CHCH2OC6F4BF3] is prepared at 100 °C whereas at 130 °C formation of 2,3,5,6-C6F4HOCH2CHCH2 occurs. Salt K[4-PhOC6F4BF3] is obtained in 82% yield using KOPh (2 equivalents) in DMSO at 130 °C.

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► A new method for preparation of potassium polyfluoroaryltrifluoroborates, K[4-ROC6F4BF3], was developed.
► This method is based on a reaction of potassium pentafluorophenyltrifluoroborate with O-nucleophiles.
► The O-nucleophiles attack a carbon center of the aromatic ring in the para-position to BF3 group of K[C6F5BF3].