Thioether Amide Based-Fluorescent Chemosensors for Pd²⁺ with High Selectivity over Pd⁰

Experimental

Chemicals. All reagents used in this work were purchased from Sigma-Aldrich Chemical Co. and were used without further purification. Pd2+ ion solution was prepared form the respective chloride anion and DMSO, other metal ion solutions solutions were prepared from the respective perchlorate anions and deionized water.

Synthesis of N-(2-(Methylthio)ethyl)pyrene-1-carboxamide (1). To a solution of 1-pyrenecarboxylic acid (0.25 g, 1.0 mmol) in CH2Cl2 (20 mL), were added oxalyl chloride (0.38 g, 3.0 mmol) and 2 drops of DMF. After stirring for 3 h at room temperature, the solvent was removed under reduced pressure. The resulting solid was dissolved in CH2Cl2 (20 mL), and then TEA (2.0 g, 20 mmol) and 1-(methylthio) ethylamine (0.14 g, 1.5 mmol) were added. After stirring for 1 h at room temperature, the solvent was removed under reduced pressure. The product was purified by silica gel chromatography with EA:Hex (1:1) as eluent. The solid product was recrystallized from MeOH to give a white solid (0.20 g, 63%): mp 161-162 °C; 1H NMR (600 MHz, CDCl3) δ 2.20 (s, 3H), 2.88 (t, 2H), 3.84 (q, 2H), 6.56 (br s, 1H), 8.03-8.23 (m, 8H), 8.61 (d, 1H); 13C NMR (150 MHz, CDCl3) δ 15.06, 34.06, 38.28, 124.34, 124.40, 124.41, 124.60, 124.78, 125.74, 125.82, 126.33, 127.11, 128.62, 128.69, 128.73, 130.70, 130.83, 131.16, 132.60, 169.98. HRMS (ESI) m/z calcd for C20H18NOS [M + H]+ 320.1109; found, 320.1100.

Synthesis of N-(2-(Methylthio)ethyl)-2-(pyren-1-yl)- acetamide (2). N-hydroxysuccinimide (0.14 g, 1.2 mol) and DCC (0.25 g, 1.2 mmol) were added to a solution of 1- pyreneacetic acid (0.26 g, 1.0 mmol) in 1,4-dioxane (20 mL). The solution was stirred for 20 h at room temperature. Ethyl acetate (30 mL) was added, and the resulting slurry was filtered. The filtrate was concentrated, the resulting solid was dissolved in 1,4-dioxane (20 mL), and 1-(methylthio) ethylamine (0.14 g, 1.5 mmol) was added. After stirring for 1 h at room temperature, the solvent was removed under reduced pressure. The product was purified by silica gel chromatography eluting with EA:CH2Cl2 (1:2) to give a yellow solid (0.18 g, 55%): mp 140-141 °C; 1H NMR (600 MHz, CDCl3) δ 1.85 (s, 3H), 2.43 (t, 2H), 3.33 (q, 2H), 4.31 (s, 2H), 5.64 (br s, 1H), 7.92-8.22 (m, 9H); 13C NMR (150 MHz, CDCl3) δ 14.94, 33.58, 38.10, 42.09, 122.97, 124.63, 125.13, 125.20, 125.43, 125.54, 126.25, 127.32, 127.63, 128.25, 128.44, 128.54, 129.60, 130.80, 131.11, 131.29, 171.02. HRMS (ESI) m/z calcd for C21H20NOS [M + H]+ 334.1266; found, 334.1255.