Photoexcited Pd(II) Auxiliaries Enable Light-Induced Control in C(sp3)-H Bond Functionalisation

We report a novel and general method for inert C(sp3)-H bond bromination, chlorination and iodination with alkyl halides. This protocol relies on the visible light irradiation of palladacycle intermediates derived from 8-aminoquinoline ligands, commonly used auxiliaries in C-H activation. The Pd(II) complex undergoes photoinduced electron transfer with alkyl halides generating C(sp3)-H halogenation products rather than C-C bond adducts. This unusual reactivity arises from a visible light induced mixed LLCT/MLCT charge transfer and preliminary mechanistic investigations implicate a mononuclear Pd(III) species which promotes C-X bond formation via a distinct Pd(III)/Pd(IV) pathway. Overall, this new mode of C(sp3)-H activation enables a straighforward and predictable access to halogenated products, providing exceptional control over the thermally induced Pd(II)/Pd(IV) activation pathway via simple irradiation with visible light.