Bis(pentafluorophenyl)borinic Acid: a Cyclic Trimer in the Solid State and a Monomer, with Hindered Rotation around the B−OH Bond, in Solution

The title molecule in the solid state exists as a cyclic trimer, with B−O(H)−B bridges and a cyclohexane-like structure ( C 2 twist-boat conformation); dissolution in toluene- d 8 affords the B(C 6 F 5 ) 2 OH monomer, in which the low-temperature 19 F NMR data reveal restricted rotation of the OH substituent around the Ar 2 B−OH bond ( E a = 39 kJ mol - 1 ), as a result of the partial double-bond character of this interaction.