Synthesis of tetraarylborates via tetralithio intermediates and the effect of polar functional groups and cations on their crystal structures

A novel general protocol for the preparation of functionalized (COOH, CHO, C(O)NHtBu, B(OH)2) tetraphenyl- and tetrakis(4'-biphenylyl)borates is reported. It involves four-fold halogen-lithium exchange in potassium tetrakis(iodophenyl)borates and tetrakis(4'-bromobiphenylyl)borate) using t-BuLi in THF at -78 °C followed by treatment of the resulting tetralithio intermediates with electrophiles (CO2, DMF, t-BuNCO, B(OMe)3). X-ray crystal structures of ammonium tetrakis[4-(dihydroxyboryl)phenyl]borate, lithium tetrakis(3-carboxyphenyl)borate, and lithium tetrakis[4-(tert-butylcarbamoyl)phenyl]borate were determined showing a strong effect of the cation and polar functional group on supramolecular architecture.