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

Abstract

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.

Mechanistic Studies of Regiocontrolled Bisaddition of Fullerenes Driven by Oriented External Electric Fields

“…To achieve such a goal, introducing an oriented external electric field (OEEF) could be a suitable way. By enhancing the intermolecular charge transfer (CT) in transition states (TSs), the OEEF along the reaction axis can effectively reduce the activation barrier and catalyze the [4 + 2] cycloaddition, which has been detected in experiments supported by the STM technology. − Moreover, by utilizing the directional response of an electric field to the dipole orientation of reactants, theoretical investigations by Shaik and co-workers proposed that a 100% R/S enantioselectivity in DA reactions can be achieved. − Accordingly, the OEEF is expected to not only enhance the reactivity but also promote the selectivity of products. − In particular, although the dipole moments of I h _symmetric C 60 and D 5 h _symmetric C 70 are vanishing, the monoadducts are polarized with the inherent dipoles pointing from the electron-accepting carbon cages to the indene motif acting as the electron donor. According to the principles of molecular electrostatics, it can be deduced that the monoadducts should be oriented along with the dipole vector under OEEFs, and therefore, we are expecting that those different sites on the fullerene monoadduct can be selectively activated or passivated to generate highly regioselective bisadducts that cannot be achieved using traditional chemical approaches.…”

Gradient bundle analysis of ketosteroid isomerase

“…Only recently have accurate assessments of electrostatic preorganization become computationally feasible, with researchers now exploring available methods for such assessments. Meanwhile, the effects of applied electric fields on chemical reactivity have been experimentally and computationally observed for a variety of chemical reactions [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24], many of which are also catalyzed enzymatically. Hence the specific problem of electrostatic preorganization, and the general problem of electric field catalysis, are of interest to enzymologists.…”

Gradient bundle analysis of ketosteroid isomerase

“…Only recently has accurate assessment of electrostatic preorganization become computationally feasible, and researchers are now exploring available methods for such assessment. Meanwhile, the effects of applied electric fields on chemical reactivity have been experimentally and computationally observed for a variety of chemical reactions [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], many of which are also catalyzed enzymatically.…”