Switchable (2 + 2) and (4 + 2) Cycloadditions on Boron Nitride Nanotubes under Oriented External Electric Fields: A Mechanistic Study.

The (2 + 2) and (4 + 2) cycloadditions are important approaches for the functional derivatizations of nanocarbon and hexagonal boron nitride (hBN) materials. However, as two competing reactions with similar reactivity, it is difficult to control the type of reactions and the corresponding adducts in practice. Here, we introduced a mechanistic study of the oriented external electric field (OEEF)-modulated cycloadditions of pristine and substituted benzynes on the zigzag boron nitride nanotubes. Owing to the distinct charge transfer directions between the competing (2 + 2) and (4 + 2) reactions and the resultant distinct responses of the barriers to the fields along the tube axis, we found that OEEF plays opposing catalytic roles in these two types of reactions and the effect of electric field as a catalyst or inhibitor can be easily reversed by flipping the field vector to achieve selective reactions and products at will.