Kinetics-controlled radical coupling on dual redox-active sites for selective formamide production.

Abstract

Catalytic construction of C-N bonds remains a pivotal challenge due to unmatched radical-radical coupling kinetics. Here, we design a redox-enhanced photosynthesis system with separated Ni²⁺-reductive and Ti^4-x-oxidative dual-active sites, achieving the regulation of generation, stabilization, and coupling of transient-stabilized radical pairs for formamide synthesis. NO₂^- and CH₃OH reactants are photo-activated on the Ni²⁺-Ti^4-x dual-active sites to generate ^●NO and CH₃^●O radicals, respectively. The ^●NO on Ni²⁺ sites is stabilized through π backbonding formation resulting from the hybridization of 3 d (Ni²⁺) and π* (^●NO) orbitals. The weak steric effect endows fast migration of transient CH₃^●O to the neighboring Ni²⁺-^●NO interface, facilitating the generation of *OC-NO intermediate, subsequently producing formamide alongside proton transfer pathways, achieving a selectivity of 99.5% and production rate of 1.66 mol g_cat^-1 h^-1. This work demonstrates principles for orbital-mediated radical stabilization and kinetics-regulated radical-radical coupling, providing a paradigm for overcoming kinetic limitations for diverse radical-mediated catalytic reactions.