Jump to main content
Jump to site search


Formylation or methylation: what determine the chemoselectivity of reactions of amine, CO2, and hydrosilane, catalyzed by 1,3,2-diazaphospholene?

Abstract

DFT computations have been performed to gain insight into the mechanisms of formylation/methylation of amines (e.g. methylaniline(1a)/2,2,4,4,-tetramethylpiperidine (2a)) with CO2 and hydrosilane ([Si]H2, [Si]=Ph2Si), catalyzed by 1,3,2-diazaphospholene ([NHP]H). Different from the generally proposed sequential mechanism for methylation of amine with CO2, i.e. methylation proceeds via formylation, followed by further reduction of formamide to give N-methylated amine, the study characterized a competition mechanism between formylation and methylation. The chemoselectivity originates from the competition between amine and [NHP]H hydride to attack formyloxy carbon of [Si](OCHO)2 (the insertion product of CO2 into [Si]H2). When the attack of an amine (e.g. 1a) wins, the transformation affords formamide (1b) and would otherwise (e.g. 2a) result in N-methylated amine (2c). The reduction of formamide by [Si]H2 or [NHP]H is highly unfavorable kinetically, thus we call attention to the sequential mechanism for understanding methylation of amine with CO2. In addition, the study has the following key mechanistic findings. The activation of CO2 by [NHP]H establishes an equilibrium: [NHP]H + CO2 ⇄ [NHP]OCHO ⇄ [NHP]+ + HCO2-. The ions play catalytic roles to promote formylation via HCO2- or methylation via [NHP]+. In 1a formylation, HCO2- initiates the reaction, giving 1b and silanol byproducts. However, after the initiation, silanol byproducts acting as hydrogen transfer shuttles are more effective than HCO2- to promote the formylation. In 2a methylation, [NHP]+ promotes the generations of the key species, formaldehyde and a carbocation species (IM17+). Our experimental study corroborates our computed mechanisms.

Back to tab navigation

Supplementary files

Publication details

The article was received on 21 Feb 2017, accepted on 06 Sep 2017 and first published on 11 Sep 2017


Article type: Edge Article
DOI: 10.1039/C7SC00824D
Citation: Chem. Sci., 2017, Accepted Manuscript
  • Open access: Creative Commons BY license
  •   Request permissions

    Formylation or methylation: what determine the chemoselectivity of reactions of amine, CO2, and hydrosilane, catalyzed by 1,3,2-diazaphospholene?

    Y. Lu, Z. Gao, X. Chen, J. Guo, Z. Liu, Y. Dang, S. Ye and Z. Wang, Chem. Sci., 2017, Accepted Manuscript , DOI: 10.1039/C7SC00824D

    This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. Material from this article can be used in other publications provided that the correct acknowledgement is given with the reproduced material.

    Reproduced material should be attributed as follows:

    • For reproduction of material from NJC:
      [Original citation] - Published by The Royal Society of Chemistry (RSC) on behalf of the Centre National de la Recherche Scientifique (CNRS) and the RSC.
    • For reproduction of material from PCCP:
      [Original citation] - Published by the PCCP Owner Societies.
    • For reproduction of material from PPS:
      [Original citation] - Published by The Royal Society of Chemistry (RSC) on behalf of the European Society for Photobiology, the European Photochemistry Association, and RSC.
    • For reproduction of material from all other RSC journals:
      [Original citation] - Published by The Royal Society of Chemistry.

    Information about reproducing material from RSC articles with different licences is available on our Permission Requests page.

Search articles by author

Spotlight

Advertisements