Novel cis-[PdCl2(NHC)(PPh3)] complex: synthesis, crystal structure, spectral investigations, DFT and NCI studies, prediction of biological activity

Abstract

This study contains the synthesis of a heteroleptic Pd(II) cis–[PdCl2(NHC)(PPh3)] complex containing an N-heterocyclic carbene (NHC) and a triphenylphosphine (PPh3) ligand. The complex was prepared from the related [PdCl2(NHC)(3–Clpy)] complex (PEPPSI), replacing the 3-chloropyridine ligand (3-Clpy) by the PPh3 ligand, and characterized by using 1H NMR, 31P NMR, 13C NMR, FT-IR, UV-vis spectroscopies and elemental analysis. The molecular and crystal structure of the complex was determined by single-crystal X-ray diffraction analysis. Comprehensive theoretical calculations including the optimized structural parameters, the HOMO–LUMO energy gap, vibrational frequencies, and chemical shifts were calculated using density functional theory (DFT) with the B3LYP/LanL2DZ//6–31G* level and compared with the experimental data. Natural population analysis (NPA), charge decomposition analysis (CDA) and natural bond analysis (NBO) were carried out. Non-covalent interaction (NCI) calculations were also performed to identify the weak non-covalent interactions from the topological analysis and the reduced gradient of the electron density of complex. Predictive study for the biological activities using PASS (prediction of activity spectra for biologically active substances) online software showed optimistic activities for the complex as an antineoplastic (melanoma) and nicotinic α6β3β4α5 receptor antagonist.