Spontaneous conversion of pyridine N-oxide ylide covalent organic framework (COF) into biradical COF as an efficient catalyst in catalytic dehydrogenation of nitrogen heterocycles

Over the past decade, covalent organic frameworks (COFs) have garnered significant attention as supporting materials for the immobilization of radical species, showing great promise in applications such as catalysis, energy storage, and dynamic nuclear polarization. While considerable progress has been made in developing monoradical COFs, the creation of COFs with embedded biradicals remains a substantial challenge. In this study, we present a novel pyridine N-oxide ylide COF, featuring an electron-withdrawing dicarboxamide group designed to facilitate the formation of a biradical COF (pyridine N-oxide biradical COF). This biradical generation occurs through a spontaneous intramolecular single-electron transfer process under ambient conditions. By integrating both electron-withdrawing and π-conjugated units into the pyridine ring, we enhance the stability and formation of biradical species. The electron paramagnetic resonance results demonstrate that the COF structure is pivotal in stabilizing and promoting biradical species formation. Further analyses, including Fourier-transform infrared, X-ray photoelectron, and ¹³C cross-polarization magic angle spinning nuclear magnetic resonance spectroscopies, confirm the coexistence of ylides and biradical species within the COF material. Additionally, the COF exhibits promising catalytic activity, serving as an efficient catalyst in the dehydrogenation of nitrogen heterocycles. This work bridges the gap between ylide COFs and biradical COFs, expanding our understanding of porous materials and their potential applications in advanced chemistry.