The Effect of Carborane Substituents on the Lewis Acidity of Boranes

The
Lewis acidity of primary, secondary, and tertiary
boranes with
phenyl, pentafluorophenyl, and all three isomers of the C-substituted
icosahedral carboranes (ortho, meta, and para) was investigated by computing their
fluoride, hydride, and ammonia affinities as well as their global
electrophilicity indices and LUMO energies. From these calculations,
it was determined that the substituent effects on the Lewis acidity
of these boranes follow the trend of ortho-carborane
> meta-carborane > para-carborane
> C6F5 > C6H5.