Competition between N and O: use of diazine N-oxides as a test case for the Marcus theory rationale for ambident reactivity

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dc.contributor.author Sheehy, Kevin
dc.contributor.author Bateman, Lorraine M.
dc.contributor.author Flosbach, Niko T.
dc.contributor.author Breugst, Martin
dc.contributor.author Byrne, Peter A.
dc.date.accessioned 2020-08-05T14:23:54Z
dc.date.available 2020-08-05T14:23:54Z
dc.date.issued 2020-07-23
dc.identifier.citation Sheehy, K., Bateman, L. M., Flosbach, N. T., Breugst, M. and Byrne, P. (2020) 'Competition Between N and O: Use of Diazine N-Oxides as a Test Case for the Marcus Theory Rationale for Ambident Reactivity', Chemical Science, doi: 10.1039/D0SC02834G en
dc.identifier.startpage 1 en
dc.identifier.endpage 136 en
dc.identifier.issn 2041-6520
dc.identifier.issn x
dc.identifier.uri http://hdl.handle.net/10468/10357
dc.identifier.doi 10.1039/D0SC02834G en
dc.description.abstract The preferred site of alkylation of diazine N-oxides by representative hard and soft alkylating agents was established conclusively using the 1H-15N HMBC NMR technique in combination with other NMR spectroscopic methods. Alkylation of pyrazine N-oxides (1 and 2) occurs preferentially on nitrogen regardless of the alkylating agent employed, while O-methylation of pyrimidine N-oxide (3) is favoured in its reaction with MeOTf. As these outcomes cannot be explained in the context of the hard/soft acid/base (HSAB) principle, we have instead turned to Marcus theory to rationalise these results. Marcus intrinsic barriers (∆G0‡) and ∆rG° values were calculated at the DLPNO-CCSD(T)/def2-TZVPPD/SMD//M06-2X-D3/6-311+G(d,p)/SMD level of theory for methylation reactions of 1 and 3 by MeI and MeOTf, and used to derive Gibbs energies of activation (∆G‡) for the processes of N- and O-methylation, respectively. These values, as well as those derived directly from the DFT calculations, closely reproduce the observed experimental N vs O selectivities for methylation reactions of 1 and 3, indicating that Marcus theory can be used in a semi-quantitative manner to understand how the activation barriers for these reactions are constructed. It was found that N-alkylation of 1 is favoured due to the dominant contribution of ∆rG° to the activation barrier in this case, while O-alkylation of 3 is favoured due to the dominant contribution of the intrinsic barrier (∆G0‡) for this process. These results are of profound significance in understanding the outcomes of reactions of ambident reactants in general. en
dc.description.sponsorship Irish Research Council (GOIPG Scholarship (IRC GOIPG/2018/1517)); Verband der Chemischen Industrie (Fonds der Chemischen Industrie (Liebig scholarship)) en
dc.format.mimetype application/pdf en
dc.language.iso en en
dc.publisher Royal Society of Chemistry en
dc.relation.uri https://pubs.rsc.org/en/Content/ArticleLanding/2020/SC/D0SC02834G
dc.rights © The Royal Society of Chemistry 2020. Open Access. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. en
dc.rights.uri https://creativecommons.org/licenses/by/3.0/ en
dc.subject Diazine N-oxides en
dc.subject Marcus theory en
dc.subject Alkylation en
dc.title Competition between N and O: use of diazine N-oxides as a test case for the Marcus theory rationale for ambident reactivity en
dc.type Article (peer-reviewed) en
dc.internal.authorcontactother Peter Byrne, Chemistry, University College Cork, Cork, Ireland. +353-21-490-3000 Email: peter.byrne@ucc.ie en
dc.internal.availability Full text available en
dc.date.updated 2020-08-04T01:03:32Z
dc.description.version Accepted Version en
dc.internal.rssid 529323134
dc.contributor.funder Science Foundation Ireland en
dc.contributor.funder Irish Research Council en
dc.contributor.funder Verband der Chemischen Industrie en
dc.description.status Peer reviewed en
dc.identifier.journaltitle Chemical Science en
dc.internal.copyrightchecked No
dc.internal.licenseacceptance Yes en
dc.internal.IRISemailaddress peter.byrne@ucc.ie en
dc.relation.project info:eu-repo/grantAgreement/SFI/SFI Research Infrastructure Programme/15/RI/3221/IE/Process Flow Spectroscopy (ProSpect); Advanced Reaction Understanding using Flow Nuclear Magnetic Resonance (NMR) and Infrared (IR) Spectroscopies, with On-Line Ultra-Performance Liquid Chromatography (UPLC) and Mass Spectrometry (MS)/ en
dc.relation.project info:eu-repo/grantAgreement/SFI/SFI Research Centres/12/RC/2275/IE/Synthesis and Solid State Pharmaceutical Centre (SSPC)/ en
dc.identifier.eissn 2041-6539


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© The Royal Society of Chemistry 2020. Open Access. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. Except where otherwise noted, this item's license is described as © The Royal Society of Chemistry 2020. Open Access. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
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