Synthesis, crystal structure, spectral characterization, catalytic studies and computational studies of Ni(II) and Pd(II) complexes of symmetrical tetradentate Schiff base ligand

Abstract

In the current work, a symmetrical tetradentate Schiff base ligand (H2L) derived by the condensation of methoxy-salicylaldehyde with substituted phenylenediamine is used to prepare nickel (II) and palladium (II) complexes. The chemical structures of the synthesized compounds were investigated with the help of combustion analysis and spectrophotometrically using FT-IR and 1H NMR. H2L and its nickel (II) complex were obtained in pure crystalline form, and hence, these compounds were characterized by diffraction analysis. It was evident from single-crystal X-ray diffraction analysis (SC-XRD) that the ligand was doubly deprotonated (L−2 ) and coordinated with the Ni(II) ion via ONNO-donor sites, and a distorted square planar geometry was achieved. Interestingly, the complex also attaches a solvent molecule (DMF) through its electronegative O atom with the H atom of DMF through hydrogen bonding. The molecular structure of the synthesized compounds was further validated with the help of density functional theory (DFT) using the B3LYP/Def2-TZVP level of theory. Furthermore, the Pd(II) complex was tested for Suzuki–Miyaura cross-coupling reactions and the results showed better catalytic activity in mild conditions concerning the traditionally available catalysts.