Ruthenium(II) carbonyl complexes with phosphine-functionalized PNS type thiosemicarbazone ligands [RuCl(CO)(EPh₃)(L)] (1–6) (E = P or As, L = 2-(2-(diphenylphosphino)benzylidene) thiosemicarbazone (PNS-H), 2-(2-(diphenylphosphino)benzylidene)-N-methylthiosemicarbazone (PNS-Me), 2-(2-(diphenylphosphino)benzylidene)-N-phenylthiosemicarbazone (PNS-Ph)) have been synthesized and characterized by elemental analysis and spectroscopy (IR, UV-Vis, ¹H, ¹³C, ³¹P-NMR) as well as ESI mass spectrometry. The molecular structures of complexes 1, 2 and 6 were identified by means of single-crystal X-ray diffraction analysis. The analysis revealed that all the complexes possess a distorted octahedral geometry with the ligand coordinating in a uni-negative tridentate PNS fashion. All the ruthenium complexes (1–6) were tested as catalyst for N-alkylation of heteroaromatic amines with alcohols. Notably, complex 2 was found to be a very efficient and versatile catalyst towards N-alkylation of a wide range of heterocyclic amines with alcohols. Complex 2 can also catalyze the direct amination of 2-nitropyridine with benzyl alcohol to the corresponding secondary amine. Furthermore, a preliminary examination of performance for N,N-dialkylation of diamine showed promising results, giving good conversion and high selectivity. In addition, N-alkylation of ortho-substituted anilines (–NH₂, –OH and –SH) led to the one-pot synthesis of 2-aryl substituted benzimidazoles, benzoxazoles and benzothiazoles, also revealing the catalytic activity of complex 2.

As a contribution to the development of new ruthenium complexes with pharmacologically interesting properties, two new mononuclear ruthenium(II) complexes of the general formula [Ru(H-Nap-sbdtc)Cl(CO)(EPh₃)₂] (1 & 2) [H-(Nap-sbdtc) = 2-hydroxy-1-naphthaldehyde-S-benzyl-dithiocarbazate; E = P or As] were synthesized. The new ruthenium(II) carbonyl complexes are remarkably stable and were obtained in good yields. Their identities have been established by satisfactory elemental analyses and various spectroscopic techniques (IR, UV/visible, (¹H, ¹³C, and ³¹P) NMR, and ESI-MS). For a better definition, the molecular structure of complexes 1 and 2 has been determined by X-ray crystallography, which confirms the coordination mode of the ligand and reveals a distorted octahedral geometry around the ruthenium ion. The molecular structure of complexes 1 and 2 has been optimized by DFT calculations. The binding affinity and binding mode of the ligand and their ruthenium(II) complexes toward calf thymus CT-DNA were determined by the emission spectral method, the fluorescent indicator displacement (FID) assay and viscosity measurements. Further, the interactions of the ligand and their complexes 1 and 2 with bovine serum albumin (BSA) were investigated using UV-Vis and fluorescence spectroscopic methods. Absorption and emission spectral studies indicate that complexes 1 and 2 interact with CT-DNA and BSA protein more strongly than their parent ligand. In addition, the interactions of the complexes with DNA/BSA were followed by electrophoretic mobility spectrometry studies and the results show that these complexes exhibited good cleavage properties. In vitro anticancer activity has been scrutinized by the MTT assay, acridine orange/ethidium bromide (AO/EB) and diamidino-2-phenylindole (DAPI) staining against the human cervical cancer (HeLa) cell line.

With the aim of assessing whether transition metal complexes might be utilized as efficient biocatalysts and biological drugs, new monofunctional nickel(II) and copper(II) complexes of types NiL (1) and CuL (2) [H₂L = N-(N′,N′-diethylaminothiocarbonyl)benzimidoyl chloride-2-aminoacetophenone-N-methylthiosemicarbazone] were synthesized. The compounds are remarkably stable and were obtained in good yields. Structural elucidation was carried out thoroughly in solid and solution-states by elemental analysis and various spectroscopy techniques (IR, UV-vis, ¹H NMR, and EPR) as well as ESI mass spectrometry. The molecular structure of the compounds was investigated by single-crystal X-ray diffraction. The analyses showed tetradentate coordination of the ligand in nickel(II) and copper(II) complexes, in which the metal atom exhibits a square planar geometry with N₂S₂ in a donor fashion. Structural optimization, HOMO–LUMO energy calculations and Natural Bond Orbital (NBO) analysis of H₂L and its complexes (1 and 2) were investigated by Density Functional Theory (DFT). The trend in binding affinities of the compounds with biomolecules, such as calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) protein, were investigated by different spectrophotometric methods, which revealed an intercalative mode of interaction. Furthermore, enzyme kinetic studies reflected that the square planar complexes (1 and 2) are also effective in mimicking catecholase (3,5-DTBC) and phosphatase (4-NPP) activities over the parent H₂L. The high k_cat values suggested that the selected compounds displayed a high rate of catalytic efficiency. In vitro cytotoxicity of the complexes on human skin cancer melanoma (A375), human cervical cancer (HeLa) and human hepatocellular carcinoma (Hep3B) cancer cell lines demonstrated that the complexes had a broad-spectrum of anti-cancer activity with low IC₅₀ values. The morphological assessment data obtained by acridine orange/ethidium bromide (AO/EB) and diamidino-2-phenylindole (DAPI) staining revealed that complex 2 induces apoptosis much more effectively than 1.