Electron accepting abilities of arylborane derivatives: Effect of fluorine substituents

The structures of neutral monomeric RnBH3−n and the radical anions (R = C6H5 and C6F5) have been optimized using density functional theory (B3LYP and BP86 methods) in order to evaluate their neutral-anion energy separations as indicated by their adiabatic electron affinities (EAad), vertical electron affinities (EAvert), and vertical detachment energies (VDEs). Substitution of hydrogen by C6H5 or substitution of C6H5 by C6F5 is seen to increase greatly the neutral-anion energy separations. The B-C bond rotation barriers in the neutral C6X5BH2 derivatives (X = H, F) at 8-11 kcal/mol are lower than those in the corresponding anions at 15-21 kcal/mol. The highest neutral-anion energy separations are found in (C6F5)3B, consistent with its strong Lewis acidity relating to its use as a cocatalyst in olefin polymerization systems.