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

ABSTRACT: 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-d3 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 CO2 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.

SUBMITTER: Bhattacherjee A 

PROVIDER: S-EPMC6853971 | biostudies-literature | 2019 Nov

REPOSITORIES: biostudies-literature