10.1021/ja506228u.s001
Nathan
A. Romero
Nathan
A.
Romero
David A. Nicewicz
David A.
Nicewicz
Mechanistic
Insight into the Photoredox Catalysis
of Anti-Markovnikov Alkene Hydrofunctionalization Reactions
American Chemical Society
2015
disulfide bond
photoredox catalyst
proton transfer step
H atom donation
alkene cation
photolytic cleaveage
alkene hydrofunctionalization reactions
PhSH
activation barrier
PMN
Photoredox Catalysis
DFT
HAT catalysts
HAT step
Mechanistic Insight
PhS
Transition structure analysis
hydrogen atom transfer
2015-12-17 06:17:44
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Mechanistic_Insight_into_the_Photoredox_Catalysis_of_Anti_Markovnikov_Alkene_Hydrofunctionalization_Reactions/2045244
We describe our efforts to understand
the key mechanistic aspects
of the previously reported alkene hydrofunctionalization reactions
using 9-mesityl-10-methylacridinium (<b>Mes-Acr</b><sup><b>+</b></sup>) as a photoredox catalyst. Importantly, we are able
to detect alkene cation radical intermediates, and confirm that phenylthiyl
radical is capable of oxidizing the persistent acridinyl radical in
a fast process that unites the catalytic activity of the photoredox
and hydrogen atom transfer (HAT) manifolds. Additionally, we present
evidence that diphenyl disulfide ((<b>PhS</b>)<sub>2</sub>)
operates on a common catalytic cycle with thiophenol (<b>PhSH)</b> by way of photolytic cleaveage of the disulfide bond. Transition
structure analysis of the HAT step using DFT reveals that the activation
barrier for H atom donation from <b>PhSH</b> is significantly
lower than 2-phenylmalononitrile (<b>PMN)</b> due to structural
reorganization. In the early stages of the reaction, <b>Mes-Acr</b><sup><b>+</b></sup> is observed to engage in off-cycle adduct
formation, presumably as buildup of <b>PhS</b><sup>−</sup> becomes significant. The kinetic differences between <b>PhSH</b> and (<b>PhS</b>)<sub>2</sub> as HAT catalysts indicate that
the proton transfer step may have significant rate limiting influence.