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Title: Direct Sₙ2 or Sₙ2X manifold─mechanistic study of ion-pair-catalyzed carbon(sp³)-carbon(sp³) bond formation
Authors: Lee, Richmond
Chao, Chi Bong Eric
Ban, Xu
Tan, Siu Min
Yu, Haibo
Hyland, Christopher J. T.
Tan, Choon-Hong
Keywords: Science::Chemistry
Issue Date: 2022
Source: Lee, R., Chao, C. B. E., Ban, X., Tan, S. M., Yu, H., Hyland, C. J. T. & Tan, C. (2022). Direct Sₙ2 or Sₙ2X manifold─mechanistic study of ion-pair-catalyzed carbon(sp³)-carbon(sp³) bond formation. Journal of Organic Chemistry, 87(6), 4029-4039.
Project: RG1/19
Journal: Journal of Organic Chemistry
Abstract: Density functional theory (DFT) is used in this work to predict the mechanism for constructing congested quaternary-quaternary carbon(sp3)-carbon(sp3) bonds in a pentanidium-catalyzed substitution reaction. Computational mechanistic studies were carried out to investigate the proposed SN2X manifold, which consists of two primary elementary steps: halogen atom transfer (XAT) and subsequent SN2. For the first calculated model on original experimental substrates, XAT reaction barriers were more kinetically competitive than an SN2 pathway and connect to thermodynamically stable intermediates. Extensive computational screening modeling was then done on various substrate combinations designed to study the steric influence and to understand the mechanistic rationale, and calculations reveal that sterically congested substrates prefer the SN2X manifold over SN2. Different halides as leaving groups were also screened, and it was found that the reactivity increases in the order of I > Br > Cl > F, in agreement with the strength of C-X bonds. However, DFT modeling suggests that chlorides can be a viable substrate for the SN2X process, which should be further explored experimentally. ONIOM calculations on the full catalyst model predicted the correct stereochemical outcome, and further catalyst screening with cationic Me4N+ and K+ predicted that pentanidium is still the choice for SN2X C-C bond formation.
ISSN: 0022-3263
DOI: 10.1021/acs.joc.1c02782
Rights: © 2022 American Chemical Society. All rights reserved.
Fulltext Permission: none
Fulltext Availability: No Fulltext
Appears in Collections:SPMS Journal Articles

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