Synthesis, substitution kinetics, DNA/BSA binding and cytotoxicity of tridentate N^E^N (E = NH, O, S) pyrazolyl palladium(II) complexes

The pincer complexes, [Pd( L 1 )Cl]BF 4 ( PdL 1 ), [Pd( L 2 )Cl]BF 4 ( PdL 2 ) , [Pd( L 3 )Cl]BF 4 ( PdL 3 ), [Pd( L 4 )Cl]BF 4 ( PdL 4 ) were prepared by reacting the corresponding ligands, 2,6-bis[(1H-pyrazol-1-yl)methyl]pyridine ( L 1 ), bis[2-(1H-pyrazol-1-yl)ethyl]amine ( L 2 ), bis[2-(1H-pyrazol-1-yl)ethyl]ether ( L 3 ), and bis[2-(1H-prazol-1-yl)ethyl]sulphide ( L 4 ) with [PdCl 2 (NCMe)] 2 in the presence NaBF 4 . The solid‐state structures of complexes PdL 1 – PdL 4 confirmed a tridentate coordination mode, with one chloro ligand completing the coordination sphere to afford square-planar complexes. Chemical behaviour of the complexes in solution confirms their stability in both aqueous and DMSO stock media. The electrochemical properties of the compounds showed irreversible two-electron reduction process. Kinetic reactivity of Pd complexes with the biological nucleophiles viz, thiourea ( Tu ), L-methionine ( L-Met ) and guanosine 5′-diphosphate disodium salt ( 5’-GMP ) followed the order: PdL 2