Supramolecular nickel complex based on thiosemicarbazone. Synthesis, transfer hydrogenation and unexpected thermal behavior

The cationic thiosemicarbazone complex of nickel containing triphenylphosphine as coligand was synthesized through the isopropanol-assisted hydrogen transfer reaction. The thiosemicarbazone ligand (LH2) and its cationic nickel complex, [Ni(LH)(PPh3)]+Cl−·(CH3)2CHOH, were characterized by elemental analysis, IR, 1H NMR and UV–Vis spectroscopies. The molecular structure of the complex was also determined by single crystal X-ray diffraction technique. In addition computational studies at B3LYP/6-311G(d,p) (main group) and LANL2DZ (Ni) level were carried out for theoretical characterization of the ligand and complex. Structural analysis of the complex indicated the presence of square-planar coordination geometry (ONNP) about nickel in which the thiosemicarbazone ligand coordinated as mononegative tridentate. Isopropyl alcohol catalyzed efficiently the transfer hydrogenation and the cationic complex formed through inter conversion azinyl–azinylidene. All spectral data support the formation of the ligand and its nickel complex and the results calculated using theoretical methods coincide well with the experimental findings. The thermal degradation of the complex was investigated using thermogravimetric and differential thermal analyses techniques in nitrogen and oxygen atmosphere. The oxidative-thermal decomposition of the compound showed volatilization of nickel as unexpected behavior unlike nitrogen atmosphere.

The large energy gap of 3.519 eV between the HOMO (H) and the LUMO (L) indicates that the complex, [Ni(LH)(PPh3)]+Cl−·(CH3)2CHOH, is very stable. This paper presents that isopropylalcohol catalyzes efficiently the transfer hydrogenation and a supramolecular structure forms. The oxidative thermal decomposition shows volatilizing nickel complex.Figure optionsDownload as PowerPoint slide