Benign synthesis of carboxamide ligands, H2Me2bqb and H2Me2bpb. Preparation, characterization and electrochemistry of Ni(II) complexes: The crystal structure of [NiII(Me2bqb)]

A novel and highly efficient approach for the synthesis of H2Me2bqb and H2Me2bpb using ionic liquid as an environmentally benign reaction medium has been developed, eliminating the need for the pyridine as a toxic solvent. The Ni(II) complex of the dianionic ligand Me2bqb2−, [Me2bqb2− = 1,2-bis(quinoline-2-carboxamide)-4,5-dimethyl-benzene dianion], has been synthesized and characterized by elemental analyses and spectroscopic methods, and the crystal and molecular structure of [Ni(Me2bqb)] (1), has been determined by X-ray crystallography. The complex exhibits distorted square-planar NiN4 coordination geometry with two short and two long Ni–N bonds (Ni–N ∼1.85 and ∼1.96 Å, respectively). The electrochemical behavior of [Ni(Me2bqb)] (1), has been studied by cyclic voltammetry and compared with the analogous complex, [Ni(Me2bpb)] (2).

The benign synthesis and characterization of H2Me2bqb and H2Me2bpb ligands using molten ionic liquid as the reaction media are reported. The toxic pyridine used in the classical method has been replaced by TBAB. The [NiII(Me2bqb)] and [NiII(Me2bpb)] complexes have also been prepared and structurally characterized. The redox potentials of the coordinated ligands and the metal center are influenced by the inductive effect from the methyl substituents, structural distortions, and charge delocalization by the fused phenyl rings in Me2bqb.Figure optionsDownload as PowerPoint slide