Article 3Regulating electron transfer over asymmetric low-spin Co (II) for highly selective electrocatalysis

Kuang-Hsu Wu*, Yuefeng Liu, Xin Tan, Yangyang Liu, Yangming Lin, Xing Huang, Yuxiao Ding, Bingjian Su, Bingsen Zhang, Jinming Chen, Wensheng Yan, Sean C. Smith, Ian R. Gentle*,  Shenlong Zhao*

Chem Catalysis 2(2), 372-385, (2022)
DOI: https://www.cell.com/chem-catalysis/pdf/S2667-1093(21)00375-4.pdf

Abstract

Modulating the steric-electronic configuration of metal-organic centers is key for tuning the activity and selectivity of heterogeneous reactions, especially multi-electron transfer reactions. Here, three different asymmetric metal-organic complexes with unique stericelectronic structures are immobilized on nanocarbon for an electron-transfer-controlled oxygen reduction reaction. 

The strong-field ligand-induced low-spin (LS) CoII creates a necessary steric configuration for regulating reaction selectivity through ligand’s proton transfer ability, for which acidic diamine ligands facilitate a fourelectron transfer (94%), whereas basic ligands drive a highly selective two-electron route (97%). 

The steric-electronic regulation of the reaction selectivity at catalytic sites is characterized using X-ray absorption spectroscopy, reaction kinetic path analysis, and density functional theory calculation. Our results indicate that an
LS state of CoII with asymmetric coordination is necessary to form a unique ‘‘flytrap’’ structure to promote O2 capture for the subsequent proton-coupled electron transfer, which is regulated by the Brønsted acidity of coordinating ligands.