Recent Advances in the NHPI–PINO Catalytic Cycle: Photochemical, Electrochemical, and Heterogenized NHPI/PINO Catalysis

Abstract

N-hydroxyphthalimide (NHPI) has emerged as a versatile organocatalyst for the selective oxidation and functionalization of C(sp3)–H bonds via the phthalimide N-oxyl (PINO) radical. In recent years, the NHPI–PINO platform has advanced significantly, driven by three key developments: photochemical activation, electrochemical transformation, and catalyst immobilization. Visible-light-driven systems and semiconductor-assisted photocatalysis have expanded the reaction scope and enabled sustainable transformations under mild conditions. Electrochemical approaches have provided scalable and energy-efficient routes for hydrogen atom transfer and radical functionalization, while cooperative electrocatalysis has further enhanced both activity and selectivity. Immobilizing NHPI on porous frameworks and hybrid supports has bridged the gap between homogeneous and heterogeneous catalysis, improving stability, recyclability, and compatibility with continuous-flow systems. This review summarizes mechanistic insights and key breakthroughs from 2022 onward, highlighting the integration of advanced materials, operando spectroscopy, and computational modeling. Current challenges and future opportunities are also discussed, with a focus on hybrid catalytic platforms and the expansion of applications in synthetic, industrial, and sustainable chemistry.