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.</p

Bis(1-methyl-ortho-carboranyl)borane.

The Lewis superacid, bis(1-methyl-ortho-carboranyl)borane, is rapidly accessed in two steps. It is a very effective hydroboration reagent capable of B−H addition to alkenes, alkynes, and cyclopropanes. To date, this is the first identified Lewis superacidic secondary borane and most reactive neutral hydroboration reagent

Borataalkene Hydrofunctionalization Reactions

The hydrofunctionalization of alkenes is a foundational class of reactions; however, the analogous reactions for B═C bond-containing species have been virtually unexplored. This work unearths a range of B═C hydrofunctionalization reactions with the 9-borataphenanthrene anion, including hydroalkylation, hydroarylation, hydroalkynylation, hydroamination, hydroalkoxylation, and hydration. The unique reactivity represents an addition to the synthetic chemist's toolbox to access functionalized tetracoordinate borates.</p