Year: 2025
Type: article
Abstract: High Resolution Image Download MS PowerPoint Slide Iron complexes are known for their excellent reactivity toward the oxygen reduction reaction (ORR), which proceeds via two possible pathways: a two-electron/two-proton (2e – /2H + ) process to form hydrogen peroxide or a four-electron/four-proton (4e – /4H + ) process to form water. Developing catalysts that enable selective oxygen reduction remains a challenge. Inspired by heme-based systems, we designed two iron complexes incorporating secondary coordination sphere interactions to investigate their influence on the ORR selectivity. The complexes, [Py 2 Py(afa Cy ) 2 Fe]OTf 2 and [N(afa Cy ) 3 Fe]OTf 2, were evaluated for their catalytic activity using decamethylferrocene as the reductant, with reaction progress monitored via absorbance spectroscopy. [Py 2 Py(afa Cy ) 2 Fe]OTf 2 exhibited a selectivity profile comparable to iron porphyrin but with a slower kinetic rate, likely due to the steric hindrance from ligand functionalization. [N(afa Cy ) 3 Fe]OTf 2 demonstrated exceptional selectivity toward the 2e – /2H + pathway, a rare observation for nonheme iron complexes. Kinetic measurements revealed that the catalytic reaction with [N(afa Cy ) 3 Fe]OTf 2 follows second-order kinetics with a rate constant of 81 mM –1 s –1 . We propose that the rate-determining step involves electron transfer from decamethylferrocene to the hydroperoxo iron(III) complex, occurring through a stepwise proton transfer/electron transfer (PTET) or electron transfer/proton transfer (ETPT) process, followed by hydrogen peroxide dissociation.
Source: JACS Au
Authors: Hsien-Liang Cho, Daoyang Zhang, Alison R. Fout
Institution: Texas A&M University
Language: English
Subfield: Inorganic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,500
Funder: Basic Energy Sciences
Award: G758496851
OpenAlex ID: W4411204980