Electronic Effects on the Depropargylation Process in the Reaction-based Fluorescent Detection of Palladium Species: Benzocoumarin-based Ratiometric Sensing Systems

摘要

The palladium catalyzed cross-coupling reactions are indispensable in organic synthesis of pharmaceutical compounds,demanding convenient tools for the analysis of residual palladium contents.Propargyl aryl ether-type fluorescent sensing systems that detect Pd(0)/Pd(II)/Pd(IV)species through depropargylation require no additives.We investigated a ratiometric sensing system based on a benzocoumarin dye;thus,three propargyl aryl ethers bearing electronically-different self-immolative linkers were synthesized and their relative response rate toward Pd(0)and Pd(II)were compared.We found that the response rate became faster when the self-immolative linker became more electron-deficient.The best-performing system sensed Pd(0)/Pd(II)species selectively against various other metal species,which is also capable of fluorescent imaging of Pd(0)/Pd(II)species in cells.The work provides us a clue to accelerate the catalytic depropargylation step,which,when combined with a novel fluorophore,would enable us to develop outperforming palladium sensing systems.