A new mononuclear nickel complex with 5,5′-dimethyl-2,2′-bipyridine: Synthesis, structural investigation and catalytic properties

Abstract

The new [Ni(dmbpy)(H2O)4]SeO4 complex (dmbpy = 5,5′-dimethyl-2,2′-bipyridine or C12H12N2), based on mononuclear nickel(II) and bi-atomic bridging ligands has been successfully synthesized by hydrothermal method. The crystals are characterized by X-ray single-crystal diffraction, crystallizing in the monoclinic system, space group P21/c. Their crystal structure consists of metallic cations octahedrally coordinated by four water molecules and two nitrogen atoms coming from the organic molecule [NiN2O4], and a selenate anion (SeO4)2-. Their crystal packing is ensured by a three-dimensional network of O-H…O hydrogen bonds between the cation and anion moieties, and π … π interactions between the pyridine rings of the organic moieties of the same layer. The thermal analysis discloses dehydration between 148 °C and 210 °C, leading to an anhydrous compound [Ni(dmbpy]SeO4. The study of vibrational absorption and Raman scattering spectra allows bringing additional information to those obtained by X-ray diffraction. The optical band gap was calculated from the UV–Vis absorbance spectra using classical Tauc relation which was found to be 3.58 eV. The catalytic evaluation of [Ni(dmbpy)(H2O)4]SeO4 on Heck and Sonogashira coupling reactions, activated by ultrasonic irradiation, results in encouraging yields for a very short times with a remarkable selectivity of the form (E) with respect to (Z) during the arylation of styrene, making this complex a promising catalyst for both types of reactions. The coupling products of the Heck and Sonogashira coupling reaction ((Z)-/(E)- Stilbene and Diphenylacetylene, respectively) were examined by 13C NMR and 1H NMR. These spectroscopic measurements provide extremely valuable information on the structure of the molecules obtained.