2 + 2] Cycloaddition and Bond Cleavage of Boron Nitride Cages with Iminoborane: A DFT Study

Abstract

We have studied the addition of reaction between iminoborane HBNH with the BnNn cages (n = 12, 16, 28 and 36) for the chemoselectivity (BN bond cleavage and expansion ring vs [2 + 2] cycloaddition) and regioselectivity (square–hexagon junctions vs hexagon–hexagon) of the reaction. Based on our results, the iminoborane molecule can either selectively break a B–N bond of the BN cages, expanding the square ring of the BN cage to a larger one at the surface, or undergo a [2 + 2]-cycloaddition on the BNNT surface. These reactions exhibit a depending on the reactive site of the cages. The square–hexagon B–N bond of the cages prefer bond-cleavage-ring-expansion processes, while hexagon–hexagon B–N bonds follow [2 + 2] cycloaddition reaction. Overall, all reactions are is exothermic while bond-cleavage-ring-expansion processes are a bit more favorable than [2 + 2] cycloadditions with smaller barrier heights. While complexes of iminoborane with hexagon–hexagon bonds at the middle of the larger cages resemble [2 + 2]-cycloaddition, BN bond cleavage also occurred and HBNH acts as a bridge at the top of the decagon. The larger values of HOMO–LUMO gaps for the most stable configurations also indicate kinetically preference the BN bond cleavage and ring expansion processes than the [2 + 2]-cycloaddition reactions.