A greener catalyst for hydroboration of imines—external electric field modify the reaction mechanism

Abstract

Usually, an extra catalyst (for example, the transition metal complexes) need to be used in catalyzing hydroboration, which involved the cost, environment, and so forth. Here, a greener and controllable catalyst—external electric field (EEF) was used to study its effect on hydroboration of N‐(4‐methylbenzyl)aniline (PhN═CHPhMe) with pinacolboane (HBPin). The results demonstrated that EEF could affect the barrier heights of both two pathways of this reaction. More significantly, flipping the direction of EEF could modify the reaction mechanism to induce a dominant inverse hydroboration at some field strength. That is to say, oriented EEF is a controlling switch for the anti‐ or Markovnikov hydroboration reaction of imines. This investigation is meaningful for the exploration of greener catalyst for chemistry reaction and guide a new method for the Markovnikov hydroboration addition. © 2019 Wiley Periodicals, Inc.

TITAN: A Code for Modeling and Generating Electric Fields—Features and Applications to Enzymatic Reactivity

“…Their introduction in the toolbox of synthetic chemists could potentially be a game changer, opening new (and more sustainable) routes toward chemical synthesis . At the same time, an increasing understanding of the role played by electrostatics in (bio)chemistry could offer new fundamental insights into a variety of phenomena associated to chemical reactivity …”

“…[1][2][3][4][5] Their introduction in the toolbox of synthetic chemists could potentially be a game changer, opening new (and more sustainable) routes toward chemical synthesis . [6][7][8][9][10][11] At the same time, an increasing understanding of the role played by electrostatics in (bio)chemistry could offer new fundamental insights into a variety of phenomena associated to chemical reactivity. [12][13][14][15][16][17] The hypothesis that the local electric fields (LEFs), induced by the charged functional groups scattered throughout any (asymmetric) protein matrix, have a profound impact on the catalytic function of enzymes, was originally put forward by Warshel in the 1970s.…”

Catalyst‐Free and Solvent‐Free Facile Hydroboration of Imines

“…Although traditional hydrogenation process using either stoichiometric reducing agents or pressurized hydrogen gas as hydrogen source are well‐exploited, the efficacy of these methodologies is restricted due to poor selectivity over other potentially reducible unsaturated functionalities, requirement of high‐pressure setup, and formation of inorganic byproducts –. In contrary, catalytic hydroboration of imines offers a moderate and efficient way to get access of diverse secondary amines –. However, only few examples of imine hydroboration have been described when compared to a variety of protocols having been developed for catalytic hydroboration of other unsaturated functionalities like carbonyl, alkyne, and alkene…”

“…Based on previously reported related literatures, a plausible mechanistic pathway for this catalyst‐free process is depicted in Scheme . It is proposed that a Lewis adduct between the imine and H‐Bpin of type A is first formed, which possibly enhances the hydridic character of the B‐H moiety of H‐Bpin via weakening of the bond– and thereby, promotes the hydride transfer to reduce the imine functionality likely via four membered cyclic transition state ( B ) in the next step.…”

External Electric Field—Phenyl interaction boosts hydrosilylation of substituted alkynes to α‐vinylsilane

“…[1][2][3][4][5] This is initially driven by the harness of electric field to achieve the reaction selectivity or obtain a desired mechanism. [6][7][8][9] To this extent, the oriented EEF was developed and used in theoretical studies more and more on the bond activations, [10][11][12][13][14][15][16][17] such as the halogen bond [10] and σ-bonds, [11,12] and chemical reactions, [18][19][20][21][22][23][24][25][26][27][28][29][30][31] such as the substitution reactions, [19] Menshutkin reaction, [20] Diels-Alder reaction, [21,22] hydroboration reaction, [23][24][25][26] and Azide-alkyne reactions. [27] Especially, one of the predictions on the Diels-Alder reaction [22] was supported in a STM-based experimental study, [32] which resolves the dilemma of how to orient the reactants and simultaneously deliver unidirectional oriented EEF pulses that bring...…”