Intramolecular Proton-Coupled Hydride Transfers with Relatively Low Activation Barriers

Title
Intramolecular Proton-Coupled Hydride Transfers with Relatively Low Activation Barriers
Publication Date
2023-07-13
Author(s)
Karton, Amir
( author )
OrcID: https://orcid.org/0000-0002-7981-508X
Email: akarton@une.edu.au
UNE Id une-id:akarton
Greatrex, Ben W
( author )
OrcID: https://orcid.org/0000-0002-0356-4966
Email: bgreatre@une.edu.au
UNE Id une-id:bgreatre
O'Reilly, Robert J
( author )
OrcID: https://orcid.org/0000-0002-5000-1920
Email: roreill6@une.edu.au
UNE Id une-id:roreill6
Type of document
Journal Article
Language
en
Entity Type
Publication
Publisher
American Chemical Society
Place of publication
United States of America
DOI
10.1021/acs.jpca.3c03166
UNE publication id
une:1959.11/55971
Abstract

We report that bifunctional molecules containing hydroxyl and carbonyl functional groups can undergo an effective transfer hydrogenation via an intramolecular proton-coupled hydride transfer (PCHT) mechanism. In this reaction mechanism, a hydride transfer between two carbon atoms is coupled with a proton transfer between two oxygen atoms via a cyclic bond rearrangement transition structure. The coupled transfer of the two hydrogens as Hδ+ and Hδ− is supported by atomic polar tensor charges. The activation energy for the PCHT reaction is strongly dependent on the length of the alkyl chain between the hydroxyl and carbonyl functional groups but relatively weakly dependent on the functional groups attached to the hydroxyl and carbonyl carbons. We investigate the PCHT reaction mechanism using the Gaussian-4 thermochemical protocol and obtain high activation energy barriers (ΔH298) of 210.5–228.3 kJ mol–1 for chain lengths of one carbon atom and 160.2–163.9 kJ mol–1 for chain lengths of two carbon atoms. However, for longer chain lengths containing 3–4 carbon atoms, we obtain ΔH298 values as low as 101.9 kJ mol–1. Importantly, the hydride transfer between two carbon atoms proceeds without the need for a catalyst or hydride transfer activating agent. These results indicate that the intramolecular PCHT reaction provides an effective avenue for uncatalyzed, metal-free hydride transfers at ambient temperatures.

Link
Citation
The Journal of Physical Chemistry Part A, 127(27), p. 5713-5722
ISSN
1520-5215
1089-5639
Pubmed ID
37368352
Start page
5713
End page
5722

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