Triarylamine-based porous coordination polymers performing both hydrogen atom transfer and photoredox catalysis for regioselective α-amino C(sp³)–H arylation

Abstract

Direct functionalization of C(sp³)-H bonds in a predictable, selective and recyclable manner has become a central challenge in modern organic chemistry. Through incorporating different triarylamine-containing ligands into one coordination polymer, we present herein a heterogeneous approach to the combination of hydrogen atom transfer (HAT) and photoredox catalysis for regioselective C-H arylation of benzylamines. The different molecular sizes and coordination modes of the ligands, tricarboxytriphenylamine (H₃ <b>TCA</b>) and tris(4-(pyridinyl)phenyl)amine (<b>NPy3</b>), in one coordination polymer consolidate the triarylamine (Ar₃N) moiety into a special structural intermediate, which enhances the chemical and thermal stability of the polymers and diminishes structural relaxation during the catalytic process. The inherent redox potentials of Ar₃N moieties prohibit the <i>in situ</i> formed Ar₃N˙⁺ to earn an electron from C(sp³)-H nucleophiles, but allow the abstraction of a hydrogen atom from C(sp³)-H nucleophiles, enabling the formation of the C(sp³)˙ radical and the cross-coupling reaction to proceed at the most electron-rich sites with excellent regioselectivity. The new heterogeneous photoredox HAT approach skips several interactions between transient species during the typical synergistic SET/HAT cycles, demonstrating a promising redox-economical and reagent-economical heterogeneous platform that has not been reported for α-amino C-H arylation to form benzylamine derivatives. Control experiments based on monoligand coordination polymers suggested that the mixed-ligand approach improved the photochemical and photophysical properties, providing important insight into rational design and optimization of recyclable photocatalysts for rapid access to complex bioactive molecules and late-stage functionalized pharmaceuticals.