Catalytic Activity Study of Synthesized Palladium(II)-Hydrazone Complexes in the Heck Reaction: Optimization of the Amount of Catalyst Loading and Reaction Time

Palladium offers various applications in the field of fine chemicals, especially as a catalyst in carbon-carbon coupling reactions. Pd2+ ions which are attached to a suitable ligand, such as a hydrazone derivative, improve the catalytic performance of palladium (Pd(II)) as a catalyst. This study focused on the catalytic performance of two synthesized Pd(II)–hydrazone complexes (Pd-L1 and Pd-L2) as catalysts in the Heck reaction. The reaction of synthesized hydrazone ligands L1 and L2 in methanol with Pd(II) chloride produced Pd-L1 and Pd-L2 complexes, respectively. Structures of the synthesized compounds were confirmed by using Fourier transform infrared (FT-IR), 1H and 13C nuclear magnetic resonance (NMR), and UV-Vis spectroscopies. The preliminary complexation study between Pd2+ cations and hydrazone ligands (L1 and L2) which showed stoichiometric of 1:1 and 1:2 formation corresponded to the metal-ligand ratio. Catalytic activity study of both complexes in the Heck reaction between 1-bromo-4-nitrobenzene and styrene at different catalyst loadings and reaction times was conducted and analyzed by using gas chromatography-flame ionisation detector (GC-FID) spectroscopy. The best catalytic activity was by using 0.5 mmol% Pd-L1 catalyst loading at 60 min of reaction time, in DMA solvent, and Na2CO3 as a base.