Herein, we studied the synthesis and the biological properties of palladium(II) complexes derived from iminophosphine ligands DPPB-3-hydroxybenzohydrazone (DPPB-HBH), DPPB-4-phenylthiosemicarbazone (DPPB-PTSC), and DPPB-thiosemicarbazone (DPPB-TSC) (DPPB = 2-(diphenylphosphino)benzaldehyde) using theoretical and experimental methods. The molecular structures of [PdCl(DPPB-HBH)]Cl, [Pd(DPPB-HBH)2]Cl2·2CH3CN, [PdCl(DPPB-PTSC)], and [PdCl(DPPB-TSC)] were characterized by various spectroscopic techniques and X-ray crystallographic for [PdCl(DPPB-HBH)]Cl, [Pd(DPPB-HBH)2]Cl2·2CH3CN, and [PdCl(DPPB-PTSC)], confirming the distorted square-planar geometry for the palladium atoms. Complexes with the general formula [PdCl(Ligand)x] (x = 1) were employed to evaluate biological activities such as cytotoxicity against the MDA-MB-231 breast cancer cells and DNA binding ability. The results revealed the high cytotoxicity of the palladium complexes compared to the reference drug cisplatin (IC50 = 24.59 µg/mL), as well as their moderate binding ability to DNA through electrostatic interactions and groove binding. It was also found that [PdCl(DPPB-HBH)]Cl has the highest activity among others (IC50 = 9.3 µg/mL). Their interaction mode with DNA was investigated using molecular docking and NCI calculations, which showed complete agreement with the experimental results. Furthermore, quantum chemistry calculations were used to analyze the structure–activity relationship and introduce reactive sites, which determined the cause of the difference in the reactivity of the samples.
