Understanding the subtleties of frustrated Lewis pair activation of carbonyl compounds by N-Heterocyclic carbene/alkyl gallium pairings

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Uzelac, Marina and Armstrong, David R. and Kennedy, Alan R. and Hevia, Eva (2016) Understanding the subtleties of frustrated Lewis pair activation of carbonyl compounds by N-Heterocyclic carbene/alkyl gallium pairings. Chemistry - A European Journal, 22 (44). pp. 15826-15833. ISSN 1521-3765 (https://doi.org/10.1002/chem.201603597)

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Abstract

This study reports the use of the trisalkylgallium GaR3 (R=CH2 SiMe3 ), containing sterically demanding monosilyl groups, as an effective Lewis-acid component for frustrated Lewis pair activation of carbonyl compounds, when combined with the bulky N-heterocyclic carbene 1,3-bis(tert-butyl)imidazol-2-ylidene (ItBu) or 1,3-bis(tert-butyl)imidazolin-2-ylidene (SItBu). The reduction of aldehydes can be achieved by insertion into the C=O functionality at the C2 (so-called normal) position of the carbene affording zwitterionic products [ItBuCH2 OGaR3 ] (1) or [ItBuCH(p-Br-C6 H4 )OGaR3 ] (2), or alternatively, at its abnormal (C4) site yielding [aItBuCH(p-Br-C6 H4 )OGaR3 ] (3). As evidence of the cooperative behaviour of both components, ItBu and GaR3 , neither of them alone are able to activate any of the carbonyl-containing substrates included in this study NMR spectroscopic studies of the new compounds point to complex equilibria involving the formation of kinetic and thermodynamic species as implicated through DFT calculations. Extension to ketones proved successful for electrophilic α,α,α-trifluoroacetophenone, yielding [aItBuC(Ph)(CF3 )OGaR3 ] (7). However, in the case of ketones and nitriles bearing acidic hydrogen atoms, C-H bond activation takes place preferentially, affording novel imidazolium gallate salts such as [{ItBuH}(+) {(p-I-C6 H4 )C(CH2 )OGaR3 }(-) ] (8) or [{ItBuH}(+) {Ph2 C=C=NGaR3 }(-) ] (12).

ORCID iDs

Uzelac, Marina ORCID logoORCID: https://orcid.org/0000-0002-5060-7017, Armstrong, David R., Kennedy, Alan R. ORCID logoORCID: https://orcid.org/0000-0003-3652-6015 and Hevia, Eva ORCID logoORCID: https://orcid.org/0000-0002-3998-7506;
  • Item type:Article
    ID code:59257
    Dates:
    Date
    Event
    24 October 2016
    Published
    26 September 2016
    Published Online
    17 August 2016
    Accepted
    Notes:This is the peer reviewed version of the following article: Uzelac, M., Armstrong, D. R., Kennedy, A. R., & Hevia, E. (2016). Understanding the subtleties of frustrated Lewis pair activation of carbonyl compounds by N-Heterocyclic carbene/alkyl gallium pairings. Chemistry - A European Journal, 22(44), 15826-15833, which has been published in final form at https://dx.doi.org/ 10.1002/chem.201603597. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
    Subjects:Science > Chemistry
    Department:Faculty of Science > Pure and Applied Chemistry
    Depositing user: Pure Administrator
    Date deposited:04 Jan 2017 15:36
    Last modified:04 Dec 2024 01:17
    URI:https://strathprints.strath.ac.uk/id/eprint/59257
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