Highly efficient Pd(II) schiff base catalyst for Sonogashira reaction / Nur Husnina Nasaruddin ... [et al.]

Five symmetrical Schiff bases were successfully synthesized from the condensation reaction between salicylaldehyde and its derivatives (X= H, F, Cl, CH3 and OCH3) with 2,2-dimethyl-1,3-propanediamine. The synthesized ligands were reacted with palladium (II) acetate in 1:1 ratio, yielding palladium (II) Schiff base complexes. They were characterized through elemental analysis CHN,melting point, molar conductivity, infrared, UV-Vis, H nuclear magnetic resonance (NMR) spectroscopy and magnetic susceptibility. All Pd(II) complexes were tested as catalysts in the Sonogashira reaction. The optimization of reaction conditions was done by varying the type of bases and the amount of catalysts. The bases used for optimization were triethylamine (C6H15N), potassium carbonate (K2CO3), pyridine (C5H5N) and potassium hydroxide (KOH) where the latter was found to be at the optimum base. The amount of catalyst was varied at 0.5, 1.0, 1.5 and 2.0 mmol% respectively. The 2.0 mmol% of catalyst was found to be the best amount of catalyst indicated by the highest percent conversion of iodobenzene in 12 hours monitored using GC-FID. The temperature set for the optimization were room temperature (30°C), 60°C, 100°C and 120°C. The best temperature of reaction found was 120°C. Pd(AD1F) showed the highest percent conversion of iodobenzene with 100% conversion after 3 hours of reaction at 120°C. Hence, the Pd (II) Schiff base complex was found to be a good catalyst without the presence of Cu(I) co-catalyst. The absence of a co-catalyst avoids product contamination and eliminates the need for by-product separation.