In the first section of this thesis, five new tridentate Schiff base ligands (L 1 - L 5 ), star- shape ligand L d and their complexes were synthesized and characterized by FT-IR, UV-Vis and 1 H-NMR techniques. The crystal structure of the complexes were determined by the single crystal X-ray analysis. In addition, the optimized geometries of the ligands and nickel complexes along with their IR spectra were calculated by the density functional theory (DFT). The time-dependent-density functional theory (TD-DFT) was employed to calculate the absorption spectra of the structures and the calculated IR and absorption spectra were compared with the corresponding experimental spectra to confirm the experimental results. Due to the presence of metals in different oxidation states, and since the Schiff basees are strong ligands in stabilazing of the oxidation state, the catalytic performance of these complexes was investigated. In the second part of this project, the electrocatalytic properties of nickel (II) complexes were studied. The nickel complexes were electrochemically dispersed onto multi-wall carbon nanotubes (MWCNTs) and their electrocatalytic activity for the oxidation of methanol have been studied by cyclic voltammetry. Based on the results, the nickel complexes were found to be active catalysts in the electro-oxidation of methanol. In the next step, The catalytic potential of the synthesized Pd(II) complexes was evaluated in Suzuki–Miyaura cross-coupling reaction by choosing different arylhalides and phenylboronic acid. Comparing with complexes of phosphorus ligands, the advantage of using Schiff base is that they are air stable and moisture insensitive. Also, tridentate Schiff bases by modulating of the steric around the palladium center are appropriate ligands for catalytic reactions. Here, we reported the synthesis, characterization of NiO@TiO 2 mixed oxide compounds and evaluated the catalytic performance of NiO@TiO 2 and [NiL (PPh 3 ); (L 1 - L 5 ) complexes in reduction of para nitrophenol. Kinetic studies have shown that the reduction in the presence of NiO@TiO 2 with a higher constant rate is faster than nickel complexes. In other words formation of a p-n semiconductors may lead to the development ofynergisticeffects for effective reduction of 4-NP. In the final part of this work the catalytic properties of [Pd 3 L d (OAc) 3 ] star- shape complex and PdO/TiO 2 Nano-oxide structure were studied in reduction of para nitro phenol to para aminophenol.