Studies Toward an Ideal Fluorescence Method to Measure Palladium in Functionalized Organic Molecules: Effects of Sodium Borohydride, Temperature, Phosphine Ligand, and Phosphate Ions on Kinetics

Residual metals in fine chemicals are currently detected by using inductively coupled plasma mass spectrometry, which requires expensive instrumentation and does not have high-throughput capabilities. Although fluorescent probes can be amenable to high-throughput analyses of metals, the utility of such analyses is limited due to the lack of generality. Herein, we report a significant improvement (≈19-fold) to our previously reported catalysis-based fluorescent probe for palladium. Specifically, we found that slightly elevated temperature dramatically improved the generality of the method and that the deallylation reaction of the nonfluorescent compound 1 was accelerated by phosphate ions in aqueous media. This method was capable of detecting 0.2 ppb palladium. We demonstrated reasonably accurate palladium detection in various active pharmaceutical ingredients and highly functionalized organic compounds.