Dioxygen-promoted catalytic deformylation of aldehydes via hydrogen atom abstraction by [Fe(TPP)]2O

Abstract

Hydrogen-atom abstraction (HAA) is a fundamental step in diverse oxidative transformations, typically mediated by high-valent metal–oxo species (MO). However, direct demonstration of this process by μ-oxo-bridged iron(III) dimers remains scarce. Here, we demonstrate that the dimeric [Fe(TPP)O]₂ complex (TPP = tetraphenylporphyrin) inherently promotes HAA, with 2-phenylpropanal (2-PPA) as the substrate. Under aerobic conditions, the iron porphyrin dimer abstracts an α-carbon hydrogen atom to form a carbon-centered radical, as verified by EPR spin-trapping. A reaction of this radical with O₂ cleaves the C–C bond, affording acetophenone and a formyloxyl radical. Although the deformylation proceeds sluggishly at neutral pH (3% yield), adding triethylamine (Et₃N) regenerates the active dimer and boosts the yield to 97%. These results provide clear evidence for HAA by a μ-oxo iron(III) porphyrin dimer and underscore its promise for aerobic C–H and C–C bond activations when paired with a suitable base.