Visible Light-Induced Transition Metal Catalysis in Organic Synthesis

Visible light-induced transition metal catalysis has emerged as a transformative approach in organic synthesis, combining the gentle energy input of LEDs with the versatility of metal centres to drive novel reaction pathways. Photoexcitation of a metal complex or its ligand generates electronically excited states that engage in single-electron transfer, energy transfer or bond weakening events, thus enabling radical and polar mechanisms that are inaccessible under purely thermal conditions. By harnessing visible light, practitioners achieve selective C–H activation, cross-coupling, decarboxylative desaturation and radical relay processes at ambient temperature, often with exceptional functional-group tolerance. The integration of photocatalytic activation with d-block metals such as palladium, copper and iron has revolutionised late-stage functionalisation of complex molecules and streamlined the assembly of pharmaceutically relevant scaffolds. This sustainable paradigm leverages readily available light sources and mild reaction media to offer precise control over radical generation, minimise side-product formation and expand the chemical space accessible to modern synthetic chemists.

Research from Nature Portfolio

Recent studies have unveiled excitation of palladium catalysts as a means to access dual mechanistic manifolds. One investigation demonstrated that photoexcited Pd(0) engages in hydrogen-atom transfer and oxidative coupling to effect dehydrogenative β-sulfonylation of amines with aryl sulfonyl chlorides under blue-LED irradiation. Spectroscopic and computational analyses revealed the presence of Pd-radical hybrids capable of both inner-sphere and outer-sphere pathways, enabling efficient C–S bond formation at room temperature. Another advance introduced a secondary phosphine oxide ligand bearing a built-in photosensitiser, which upon visible-light absorption undergoes tautomerisation to a phosphinous acid. This design enables intramolecular single-electron transfer between ligand and palladium, facilitating radical cross-couplings of allyl, alkyl and aryl halides without additional photosensitisers. The light-mediated ligand-to-metal and metal-to-ligand electron transfers broaden the scope of palladium-catalysed radical C–C bond constructions under mild conditions.

Visible Light-Induced Transition Metal Catalysis in Organic Synthesis publication trend

The graph below shows the total number of articles in visible light-induced transition metal catalysis in organic synthesis across all publications each year (not limited to Nature Index journals).

Technical terms

Photoredox catalysis: Activation of a catalyst by visible light to induce redox reactions through excited electronic states.

Single-electron transfer (SET): A process in which one electron moves between species, generating radical intermediates.

Hydrogen atom transfer (HAT): Movement of a hydrogen atom (proton plus electron) from one molecule to another, often initiated by radicals.

Decarboxylative desaturation: Removal of CO₂ from a carboxylate to form an alkene via catalytic radical or ionic pathways under light irradiation.

References

1. Mechanistic insights into excited-state palladium catalysis for C–S bond formations and dehydrogenative sulfonylation of amines. Nature Communications (2023).
2. A visible-light activated secondary phosphine oxide ligand enabling Pd-catalyzed radical cross-couplings. Nature Communications (2022).
3. Selective 1,4-syn-Addition to Cyclic 1,3-Dienes via Hybrid Palladium Catalysis. ACS Central Science (2024).
4. Aryl-to-alkyl radical relay Heck reaction of amides with vinyl arenes. Chemical Science (2023).
5. Visible light-induced palladium–carbon bond weakening in catalytically relevant T-shaped complexes. Chemical Science (2023).