Salt Metathesis: Tetrafluoroborate Anion Rapidly Fluoridates Organoboronic Acids to give Organotrifluoroborates.

Tetrafluoroborate (BF 4 - ) has long been used as a spectator counter anion. Herein, we report an unprecedented salt metathesis between a variety of BF 4 - salts and a series of organoboronic acids yielding the corresponding organotrifluoroborates. We identified conditions for fast and efficient fluoridation (<1 h) with minimal workup. Fundamentally, this work discloses the proclivity of BF 4 - to exchange fluoride atoms with organoboronates, highlighting the lability of BF 4 - .