Synthesis and characterization of new bioactive palladium(II) complexes

Abstract

In the present study, 62 heteroleptic Pd(II) complexes have been synthesized by reacting PdCl2 with sodium dithiocarbamate salt and different organophosphine in mixed solvent system of methanol and acetone. The different dithiocarbamate ligands used were sodium salt of dibenzylcarbamodithioate (L1), (4-chlorobenzyl)(4-methylbenzyl)carbamodithioate (L2), benzyl(cyclopenta-1,3-dien-1-ylmethyl)carbamodithioate (L3), 4-(2-hydroxyethyl)piperazine-1-carbamodithioate (L4), 4-benzhydrylpiperazine-1-carbamodithioate (L5), dimethylcarbamodithioate (L6), diethylcarbamodithioate (L7), and bis(2-hydroxyethyl)carbamodithioate (L8). The organophosphines used were triphenylphosphine, diphenyl-p-tolylphosphine, tri-p-tolylphosphine, tris-p-chlorophenylphosphine, tris-p-fluorophenylphosphine, tri-o-tolylphosphine, tri-m-tolylphosphine, tris(4-methoxy-3,5-dimethylphenyl)phosphine, tricyclohexylphosphine, chlorodiphenylphosphine, 1,2-bis(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)propane and 1,4-bis(diphenylphosphino)butane. These complexes were characterized by different spectroscopic techniques like elemental analysis, FT-IR, multinuclear (1H, 13C and 31P) NMR and single crystal XRD. DFT calculations were also carried out for some representative complexes (1-10). The neutral complexes (1-42) showed a pseudo square planar geometry around palladium metal with two cis sites occupied by a bidentate dithiocarbamate moiety forming four-membered chelate ring (PdS2C) and the remaining two are occupied by a chloride and a monodentate organophosphine. However, in the cationic complexes (43-58) the latter cis positions are occupied by the phosphorous atoms of the bidentate organophosphine. The chlorodiphenylphosphine was oxidized in the aforementioned solvent system and unexpected products were obtained with two phosphine oxide attached to the metal center through phosphorous in cis position (59-62). Some of the representative ligands and complexes were screened for in vitro cytotoxic activity against human liver cancer cell line (HepG2) using MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide methods using doxorubicin as standard drugs. Generally, the heteroleptic Pd(II) complexes comprising bidentate organophosphine, {1,2-bis(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)propane and 1,4-bis(diphenylphosphino)butane}, fluoro and iv uncoordinated group (carbonyl and oxygen) were found to be most active as compared to the standard drug (doxorubicin). The selected Pd(II) complexes were also evaluated to check their cytotoxicity using brine shrimp assay. The highest activity was found for compounds containing oxygen and fluoro substituents.