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

• Published in: Journal of computational chemistry 2019-07, Vol.40 (19), p.1772-1779
• Main Authors: Zhang, Ming‐Xia, Xu, Hong‐Liang
• Format: Article
• Language: English
• Subjects: Aniline; anti‐ or Markovnikov hydroboration; Catalysis; Catalysts; Coordination compounds; Electric fields; external electric field; Field strength; greener catalyst; Hydroboration; Imines; Metal complexes; Organic chemistry; Reaction mechanisms; Stability; Transition metal compounds
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.25830

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. External electric field (EEF), as a greener and controllable catalyst/inhibitor, was used to study its effects on hydroboration of imines from three directions. Interestingly, when the EEF was oriented along positive Z‐axis direction, that is, the direction from N to C atom in C═N bond, the traditional anti‐Markovnikov hydroboration were suppressed with the rising of field strength. As a contrast, the Markovnikov hydroboration of imines were accelerated. More significantly, the barrier heights of Markovnikov hydroboration became even lower than that of anti‐Markovnikov hydroboration once the EEF strength are more than 185 (×10−4) au.