Picosecond to millisecond tracking of a photocatalytic decarboxylation reaction provides direct mechanistic insights

The photochemical decarboxylation of carboxylic acids is a versatile route to free radical intermediates for chemical synthesis. However, the sequential nature of this multi-step reaction renders the mechanism challenging to probe. Here, we employ a 100 kHz mid-infrared probe in a transient absorpti...

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Bibliographic Details
Published in:Nature communications Vol. 10; no. 1; pp. 5152 - 7
Main Authors: Bhattacherjee, Aditi, Sneha, Mahima, Lewis-Borrell, Luke, Tau, Omri, Clark, Ian P., Orr-Ewing, Andrew J.
Format: Journal Article
Language:English
Published: London Nature Publishing Group UK 13.11.2019
Nature Publishing Group
Nature Portfolio
Subjects:
140/125
639/638/439/890
639/638/440/950
639/638/77/885
Absorption spectroscopy
Acetonitrile
Carbon dioxide
Carboxylic acids
Chemical synthesis
Cyclohexanecarboxylic acid
Decarboxylation
Electron transfer
Free radicals
Humanities and Social Sciences
Infrared tracking
Intermediates
multidisciplinary
Organic chemistry
Phenanthrene
Photocatalysis
Photochemicals
Reaction intermediates
Science
Science (multidisciplinary)
Selectivity
ISSN:2041-1723, 2041-1723
Online Access:Get full text
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Summary:The photochemical decarboxylation of carboxylic acids is a versatile route to free radical intermediates for chemical synthesis. However, the sequential nature of this multi-step reaction renders the mechanism challenging to probe. Here, we employ a 100 kHz mid-infrared probe in a transient absorption spectroscopy experiment to track the decarboxylation of cyclohexanecarboxylic acid in acetonitrile-d 3 over picosecond to millisecond timescales using a photooxidant pair (phenanthrene and 1,4-dicyanobenzene). Selective excitation of phenanthrene at 256 nm enables a diffusion-limited photoinduced electron transfer to 1,4-dicyanobenzene. A measured time offset in the rise of the CO 2 byproduct reports on the lifetime (520 ± 120 ns) of a reactive carboxyl radical in solution, and spectroscopic observation of the carboxyl radical confirm its formation as a reaction intermediate. Precise clocking of the lifetimes of radicals generated in situ by an activated C-C bond fission will pave the way for improving the photocatalytic selectivity and turnover. The spectroscopic tracking of complex, multi-step chemical reactions is challenging due to the dynamic timescales of the elementary steps. Here, the authors track a four-step, light-induced decarboxylation reaction in real time to provide new mechanistic insights.
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ISSN:2041-1723
2041-1723
DOI:10.1038/s41467-019-13154-w