Mechanistic study on the reaction of pinB-BMes2 with alkynes based on experimental investigation and DFT calculations: gradual change of mechanism depending on the substituent

Linlin Wu; Chiemi Kojima; Ka-Ho Lee; Shogo Morisako; Zhenyang Lin; Makoto Yamashita

doi:10.1039/D1SC02863D

Mechanistic study on the reaction of pinB-BMes₂ with alkynes based on experimental investigation and DFT calculations: gradual change of mechanism depending on the substituent†

Linlin Wu,

‡^a Chiemi Kojima,‡^b Ka-Ho Lee,

^a Shogo Morisako,

^c Zhenyang Lin

*^a and Makoto Yamashita

*^c

Author affiliations

* Corresponding authors

^a Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
E-mail: chzlin@ust.hk

^b Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan

^c Department of Molecular and Macromolecular Chemistry, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603, Japan
E-mail: makoto@oec.chembio.nagoya-u.ac.jp

Abstract

Transition metal-free direct and base-catalyzed 1,2-diborations of arylacetylenes using pinB-BMes₂ provided a syn/anti-isomeric mixture of diborylalkenes. The kinetic analysis showed that the reaction rate and isomer ratio were affected by reaction conditions and substituents on the aryl ring. DFT calculations indicated that direct addition proceeded via the interaction of acetylene-π with the BMes₂ fragment. In contrast, for the base-catalyzed diboration, the previously isolated sp²–sp³ diborane and borataallene were confirmed as stable intermediates by calculations. The whole reaction pathways can be divided into the Bpin-migration and deprotonation steps, where the borataallene should be considered as a common intermediate. It should be noted that the deprotonation step is reversible and affords the kinetically less favoured isomer under the thermodynamic conditions. As a result, the composition of isomeric products, in the base-catalyzed diboration, is attributed to the small difference of activation barriers between direct and base-catalyzed systems.

This article is part of the themed collection: Most popular 2021 catalysis articles, 2021

Supplementary files

Article information

DOI: https://doi.org/10.1039/D1SC02863D
Article type: Edge Article
Submitted: 27 May 2021
Accepted: 16 Jun 2021
First published: 17 Jun 2021
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry

Download Citation

Chem. Sci., 2021,12, 9806-9815

Permissions

Request permissions

Mechanistic study on the reaction of pinB-BMes₂ with alkynes based on experimental investigation and DFT calculations: gradual change of mechanism depending on the substituent

L. Wu, C. Kojima, K. Lee, S. Morisako, Z. Lin and M. Yamashita, Chem. Sci., 2021, 12, 9806 DOI: 10.1039/D1SC02863D

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

Chemical Science