Electrophilic activation of Lewis base complexes of borane with trityl tetrakis(pentafluorophenyl)borate

Borenium ions do not accumulate under the conditions of hydride abstraction from Lewis base borane complexes (L center dot BH3) using trityl cation because subsequent rapid reaction with L center dot BH3 occurs to form B-H-B bonds. The hydride-bridged cations are sufficiently stabilized to resist abstraction of the remaining hydride by excess trityl cation; however, reversible cleavage of the 3c2e bond does take place to release borenium ion equivalents, as evidenced by interaction with weak nucleophiles.