Organosilane‐Patterned Paper‐based Colorimetric Sensors for High‐Throughput Screening of Cross‐Coupling Reactions with Aryl Bromides

An organosilane‐patterned paper‐based colorimetric sensor for bromides was developed using the 4‐(2‐pyridylazo)resorcinol (PAR)‐Hg2+ complex and patterned hydrophobic paper. The red color of the (PAR)‐Hg2+ spot was converted to yellow by ligand exchange between PAR and added bromide ions. This paper‐based sensor was applied to detect the extent of conversion of aryl bromides in palladium‐catalyzed coupling reactions such as Stille, Suzuki, Heck, direct arylation and decarboxylative coupling. A good correlation was demonstrated between the conversion of paper‐based sensor and conversion of gas chromatography.