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 (M=O). However, direct demonstrations of this process by μ-oxo-bridged iron(III) dimers remain 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. 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 a 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.