Stable Cu (I) Complexes for Intracellular Cu‐Catalyzed Azide Alkyne Cycloaddition

The copper‐catalyzed azide‐alkyne cycloaddition (CuAAC) has heralded a new era of chemical biology and biomedicine. However, caveats of CuAAC include formation of reactive oxygen species (ROS) and other copper‐related toxicity. This limits utility in sensitive biological samples and matrices. Towards addressing these caveats, we synthesized and fully characterized two air and water stable trinuclear Cu (I) dimer complexes. The complexes were stable to oxidation in the presence of hydrogen peroxide, acid, base, and other chelators, which was reasoned to be due to the linear benzimidazole‐Cu‐benzimidazole geometry. Computational investigations of the catalytic cycle implicated two of the three coppers in the trimer complex as the active metal centers. The complexes were shown to catalyze the reaction at far below sub‐toxic concentrations for intracellular click reactions to label triple negative breast cancer cells and compared to the current CuSO­4‐THPTA standard.