Photocatalytic C–H Activation with Alcohol as a Hydrogen Atom Transfer Agent in a 9‑Fluorenone Based Metal–Organic Framework

Hydrogen
atom transfer (HAT) has become an attractive strategy
for the activation of hydrocarbon feedstocks. Alcohols, as inexpensive
and efficient hydrogen transfer reagents, have limited application
in C–H functionalization due to the difficulty in the alkoxy
radical acquisition. 9-Fluorenone moieties were incorporated into
the metal–organic framework (MOF) as a photocatalyst; through
the formation of hydrogen bonds between the carbonyl group of a ligand
and alcohol, alkoxy radicals could be obtained by the visible-light-driven
oxidation of 2,2,2-trichloroethanol via proton-coupled
electron transfer (PCET). Effectively photocatalyzed intermolecular
coupling reactions between phenyl vinyl sulfone and aldehyde or cyclic
ether were realized through the HAT pathway. Compared to homogeneous
catalysts, the heterogeneous MOF photocatalyst improved the catalytic
efficiency and could be recycled at least five times. The microenvironment
of the Zn-OFDC channel was beneficial for the formation of hydrogen
bonds and stability of alkoxy radicals.