Thiosemicarbazone complexes of transition metals: Synthesis, characterization and study of reactivity

Chapter 1: In this chapter the scope of the present investigation is delineated briefly along with the aim of the work. Chapter 2: The syntheses and characterization of some new mixed-ligand nickel(II) complexes {[Ni(L1)(PPh3)] (1); [Ni(L1)(Py)] (2); [Ni(L2)(PPh3)]∙DMSO (3); [Ni(L2)(Imz)] (4), [Ni(L3)(4‒pic)] (5) and [{Ni(L3)}2(μ‒4,4′‒byp)]∙2DMSO (6)} of the selected three thiosemicarbazones {4‒(p‒X‒phenyl)thiosemicarbazone of salicylaldehyde} (H2L1‒3) are described in the present chapter, differing in the inductive effect of the substituent X (X = F, Br and OCH3), in order to observe their influence, if any, on the redox potentials and biological activity of the complexes. All the synthesized ligands and the metal complexes are successfully characterized by elemental analysis, IR, UV‒Vis, NMR spectroscopy and cyclic voltammetry. Molecular structures of four mononuclear (1‒3 and 5) and one dinuclear (6) Ni(II) complexes have been determined by X‒ray crystallography. The complexes have been screened for their antibacterial activity against Escherichia coli and Bacillus. Minimum inhibitory concentration of these complexes indicates compound 4 as the potential lead molecule for drug designing. Chapter 3: 4–(p–X–phenyl)thiosemicarbazone of napthaldehyde {where, X = Cl (HL1) and X = Br (HL2)}, thiosemicarbazone of quinoline–2–carbaldehyde (HL3) and 4–(p–fluorophenyl)thiosemicarbazone of salicylaldehyde (H2L4) and their copper(I), {[Cu(HL1)(PPh3)2Br]·CH3CN (1) and [Cu(HL2)(PPh3)2Cl]·DMSO (2)} and copper(II), {[(Cu2L32Cl)2(–Cl)2]·2H2O (3) and [Cu(L4)(Py)] (4)} complexes are reported herein. The synthesized ligands and their copper complexes were successfully characterized by elemental analysis, cyclic voltammetry, NMR, ESI–MS, IR and UV–Vis spectroscopy. Molecular vi structures of all the Cu(I) and Cu(II) complexes have been determined by X–ray crystallography. All the complexes (1–4) were tested for their ability to exhibit DNA-binding and -cleavage activity. The complexes effectively interact with CT–DNA possibly by groove binding mode, with binding constants ranging from 104 −105 M–1. Among the complexes, 3 show highest chemical (60%) as well as photo-induced (80%) DNA cleavage activity against pUC19 DNA. Finally, the in vitro antiproliferative activity of all the complexes was assayed against the HeLa cell line. Some of the complexes have proved to be as active as the clinical referred drugs, and the greater potency of 3 may be correlated with its aqueous solubility and the presence of quinonoidal group in the thiosemicarbazone ligand coordinated to the metal. Chapter 4: Oxygen atom transfer (OAT) reactivity of dioxidomolybdenum(VI) complexes [Mo(VI)O2L1‒6] (1‒6) {4–(p–bromophenyl)thiosemicarbazone of salicylaldehyde (H2L1), 4–(p–X–phenyl)thiosemicarbazone of o–vanillin {where, X = F (H2L2) and X = Cl (H2L3) and X = OMe (H2L4)}, 4–(p–bromophenyl)thiosemicarbazone of 5–bromosalicylaldehyde (H2L5), and 4–(p–chlorophenyl)thiosemicarbazone of o–hydroxynaphthaldehyde (H2L6)} with PPh3 have been investigated. The OAT reactions proceed through the formation of OPPh3, which have been characterized by 31P NMR. Dioxidomolybdenum(VI) complexes [Mo(VI)O2L1/5/6(DMSO)] (1a, 5a & 6a), [Mo(VI)O2L2/4(H2O)] (2a & 4a), and [Mo(VI)O2L3(DMSO)]4·2DMSO (3a) and monooxidomolybdenum(IV) complexes [Mo(IV)OL1‒6(N‒N)] (7‒12) {where, N‒N = 2,2'‒bipyridyl or 1,10‒phenanthroline} are reported as the product of substrate binding and oxygen atom transfer reactivity of dioxidomolybdenum(VI) complexes [Mo(VI)O2L1‒6] (1‒6) respectively. All the complexes have been spectroscopically characterized. Molecular structures of some of the Mo(VI) (1a‒4a) and Mo(IV) complexes (7 and 9‒11) have been determined by single crystal X–ray crystallography. The catalytic activity of Mo(VI) complexes (1a‒6a) have also been studied. Chapter 5: The synthesis and characterization of an oxidovanadium(IV) [VIVO(L)(acac)] (1) and two dioxidovanadium(V) [VVO2(L')] (2) and [VVO2(L)] (2a) complexes of {(4–(p–fluorophenyl)thiosemicarbazone) of pyridine–2–aldehyde} (HL) is described in the present study. The oxidovanadium(IV) species [VIVO(L)(acac)] (1) was synthesized in usual way by the reaction of metal precursor VO(acac)2 with thiosemicarbazone ligand (HL) in refluxing ethanol. The recrystallization of [VIVO(L)(acac)] (1) in DMF, CH3CN or EtOH gave the same vii product i.e. dioxidovanadium(V) complex [VVO2(L)] (2a), whereas [VVO2(L')] (2) was synthesized during recrystallization of [VIVO(L)(acac)] (1) in DMSO where the original ligand (HL) is transformed to a rearranged new ligand (HL'). The ligand in complex 1 is found to undergo methylation at the carbon centre attached to imine nitrogen in presence of DMSO and transformed to the corresponding dioxidovanadium(V) species through in situ reaction. The synthesized ligand and the metal complexes were characterized by elemental analysis, IR, UV–Vis, NMR and EPR spectroscopy. Molecular structures of complex 1 [VIVO(L)(acac)] and complex 2 [VVO2(L')] have been determined by single crystal X–ray crystallography. Complexes 1 & 2 show in vitro insulin mimetic activity against insulin responsive L6 myoblast cells, with complex 1 being more potent, is comparable to insulin at 100 μM concentration, while complex 2 has considerable insulin mimetic activity. In addition, the in vitro antiproliferative activity of the complexes 1 & 2 against the MCF–7 and Vero cell lines were also assayed. Chapter 6: 4‒(p‒methoxyphenyl)thiosemicarbazone of o‒hydroxynapthaldehyde (H2L1), 4‒(p‒methoxyphenyl)thiosemicarbazone of benzoyl pyridine (HL2) and 4–(p–chlorophenyl)thiosemicarbazone of o‒vanillin (H2L3) and their dimeric Zn(II) complexes [{ZnL1(DMSO)}2]·3DMSO (1), [{ZnL2Cl}2] (2), and a novel tetrameric Zn(II) complex [(Zn2L3)2(–OAc)2(3–O)2] (3) are reported. The synthesized ligands and their zinc complexes were characterized by elemental analysis, NMR, IR and UV–Vis spectroscopy. Molecular structures of all the complexes (1‒3) have been determined by single crystal X–ray crystallography