Visible-Light-Driven E → Z Isomerization of Olefins Catalyzed by Atomically Precise Copper Clusters

Visible-light catalysis offers a green pathway for the E → Z isomerization of olefins. However, the development of catalysts that combine high efficiency, low cost, and mild reaction conditions remains highly desired and a central challenge. To address this, we reported the gram-scale synthesis of two atomically precise copper(I) clusters─Cu₄I₄(DPPPy)₂ (DPPPy: diphenyl-2-pyridylphosphine) and Cu₂I₂(DPPPy)₃ via a facile and efficient route. Notably, the two low-cost clusters can serve as highly effective catalysts (photosensitizers) for the isomerization of diverse E-stilbene derivatives under blue LED irradiation, achieving yields of up to 89% with excellent functional group tolerance, almost equal to that of commercial iridium catalysts. Mechanistic studies reveal that the copper clusters act as light-absorbing species that engage in energy transfer with the substrates. Both theoretical calculations and spectroscopic evidence consistently identify the triplet excited state of the clusters as key to enabling substrate sensitization. This work not only opens the door to E → Z isomerization of olefins using well-defined copper clusters as alternatives to the high-cost precious-metal-based photocatalysts, but also provides a promising and cost-effective strategy for advancing sustainable visible-light catalytic processes.