Pd(OAc)2 was found to catalyze very efficiently the direct arylation of imidazo[1,2-b]pyridazine at C3-position under a very low catalyst loading and phosphine-free conditions. The reaction can be performed in very high TOFs and TONs employing as little as 0.1-0.05 mol % catalyst using a wide range of aryl bromides. In addition, some electron-deficient aryl chlorides were also found to be suitable substrates. Moreover, 31 examples of the cross couplings were reported using green, safe, and renewable solvents, such as pentan-1-ol, diethylcarbonate or cyclopentyl methyl ether, without loss of efficiency.

Six new nickel (II) complexes with a series of tetrazole derivatives functionalized by different substituents {5-(2-(1-Benzyltetrazol-5-yl) phenyl)-2-ethyl-4-methylthiazole (L 1), 1-Benzyl-5-(2-(1methylpyrrol-2-yl)phenyl) tetrazole (L 2), 5-(2-(1-Pivalyltetrazol-5-yl)phenyl)-2-ethyl-4methylthiazole (L 3), 5-(2-(1-Methylpyrrol-2-yl) phenyl)-1-pivalyltetrazole (L 4), 2-Ethyl-4-methyl-5-(2-(1 methyltetrazol-5-yl) phenyl) thiazole (L 5) and 1-Methyl-5-(2-(1-methylpyrrol-2-yl)phenyl) tetrazole (L 6)} have been synthesized and characterized by analytical and spectral methods. The data clearly indicated that the nickel (II) complexes are coordinated to the monodentate tetrazole derivatives via nitrogen (N3) atom of the tetrazole ring. The octahedral geometry is observed for all the complexes. The thermogravimetric analysis revealed the presence of coordinated and hydrated water molecules in the coordination sphere. The DFT calculations performed on both the ligands and the complexes allowed to optimize the structures, the stability and to explain the electrochemical behavior and the biological activities of the nickel (II) complexes. The study of the substituents effects on the redox properties of the ligands and their nickel (II) complexes were discussed via cyclic voltammograms. Electron donating substituents shift the reduction potentials toward negative values, while anodic shift of the oxidation potentials is manifested by the substituents having an electron withdrawing effect. The in vitro antimicrobial activities of the ligands and their corresponding nickel (II) complexes have been evaluated against four bacterial and two fungal strains.