Chemistry of Transition Metal Complexes with O- and/or N- Donor Ligands: Synthesis, Characterization and Study of Reactivity

Abstract

Chapter 1: In this chapter the scope of the present investigation is delineated briefly along with the aim of the work.
Chapter 2: The synthesis of ethoxido bridged divanadium(IV/IV) complexes [(VOL1-3)2(μ˗OEt)][Et3NH] (1‒3) of three azo dyes, 2˗(2′˗carboxy˗5′˗X-phenylazo)˗4˗methylphenol (where X = H (H2L1); X = NO2 (H2L2)) and 2˗(2′˗carboxy˗5′˗Br˗phenylazo)˗2˗naphthol (H2L3), differing in the substituents of the phenyl ring, in order to discern their influence, if any, on their redox potentials, biological activities and magnetochemistry, has been discussed. All the synthesized ligands and the vanadium(IV) complexes were successfully characterized by various physico-chemical techniques, viz. elemental analysis, IR, UV˗vis and NMR spectroscopy, ESI-MS and cyclic voltammetry. Molecular structures of [(VOL1,3)2(μ˗OEt)][Et3NH] (1 and 3) have been determined by X‒ray crystallography. Antiferromagnetic coupling interaction was observed between the vanadium d1˗d1 centers of the complexes and this phenomenon was also established theoretically. The complexes were further screened for their in vitro cytotoxicity against HeLa and HT˗29 cancer cell lines.
Chapter 3: Three new monooxidovanadium(IV) [VIVOL1–32] (1–3) and two alkoxido bridged vanadium(IV) trimeric [VIV3O3(μ˗OMe)3(μ3˗OMe)L4,52] (4 and 5), complexes have been reported, which were obtained upon reaction of 2˗˗4˗methylphenol (where X = benzo[1,3]dioxol˗5˗yl (HL1), phenyl (HL2) and 4˗methoxyphenyl (HL3)), 1˗(2˗(thiazol˗2˗yl)diazenyl)naphthalene˗2˗ol (HL4) and 2˗(2˗(thiazol˗2˗yl)diazenyl)˗4˗methylphenol (HL5)) with VOSO4.5H2O. The synthesized complexes were successfully characterized by elemental analysis, IR, UV˗vis spectroscopy, ESI˗MS and their redox properties studied by cyclic voltammetry. Molecular structure of 4 has been determined by single crystal X-ray diffraction study. The complexes were probed for their in vitro insulin˗mimetic activity against insulin responsive L6 myoblast cells. The complexes (1−5) have also been screened for their cytotoxicity in human breast adenocarcinoma cell line, MCF-7. The insulin˗mimetic activity of complexes 1−5 was also probed on rat L6 myoblast cells. To further confirm whether these compounds act via insulin signaling pathway, the immunoblot analysis for IRS˗1 was also carried out.
Chapter 4: The reaction of 2˗(arylazo)phenols (HL) with [Ru(PPh3)3Cl2] in an ethanolic medium under basic conditions afforded two organometallic Ru(II) complexes, [RuL(PPh3)2(CO)] (1) and [RuL(PPh3)2(CH3CN)] (2). A similar reaction of HL with [Ir(PPh3)3Cl] resulted in the formation of the organometallic Ir(III) complex, [IrL(PPh3)2(H)] (3). The 2˗(arylazo)phenolate ligand is coordinated to the metal center in each complex (1‒3) as a tridentate C, N, O-donor via metal assisted C‒H activation of the ligand. The plausible solvent assisted mechanistic pathway for the unprecedented CO coordination to the Ru(II) center in the case of 1 has been explained. The synthesized complexes have been characterized by various spectroscopic techniques (viz., IR, UV˗vis and NMR spectroscopy), ESI-MS and their electrochemical behavior studied by cyclic voltammetry. Molecular structures of 1‒3 have been determined by X-ray crystallography.
Chapter 5: Seven hexacoordinated cis-dioxidomolybdenum(VI) complexes, [MoO2L17] (17) derived from various substituted tetradentate diamino bis(phenolato) “salan” ligands, N,Nʹ˗dimethyl˗N,Nʹ˗bis˗(2˗hydroxy˗3˗X˗5˗Y˗6˗Z˗benzyl)˗1,2˗diaminoethane (H2L1, X = Br, Y = Me, Z = H; H2L2, X = Me, Y = Cl, Z = H; H2L3, X = iPr, Y = Cl, Z = Me) and N,Nʹ˗bis˗(2˗hydroxy˗3˗X˗5˗Y˗6˗Z˗benzyl)˗1,2˗diaminopropane (H2L4, X = Y = tBu, Z = H; H2L5, X = Y = Me, Z = H; H2L6, X = iPr, Y = Cl, Z = Me; H2L7 , X = Y = Br, Z = H) containing ON donor atoms, have been isolated and structurally characterized. The formation of cis-dioxidomolybdenum(VI) complexes was confirmed by elemental analysis, IR, UV˗vis and NMR spectroscopy, ESI˗MS and cyclic voltammetry measurements. X-ray crystallography showed the O2N2 donor set to define an octahedral geometry in each case. [MoO2L17] (1‒7) showed moderate DNA binding propensity with binding constants ranging from 104−105 M-1. The experimental results showed that the complexes 1‒7 effectively interact with CT-DNA by both minor and major groove binding mode, while complex 2 additionally interacts by partial intercalative mode of binding. The dioxidomolybdenum(VI) complexes (1‒3) showed moderate photo-induced cleavage of pUC19 supercoiled plasmid DNA. All the complexes (1–7) were tested for their in vitro antiproliferative activity against HT-29 and HeLa cancer cell lines. Some of the complexes proved to be as active as the clinical referred drugs, and the greater potency of 6 and 7 may be dependent on the substituents in the salan ligand environment coordinated to the metal.
Chapter 6: The synthesis and characterization (elemental analysis, UV˗vis spectroscopy, ESI-MS and cyclic voltammetry) of Cu(II) complexes ([CuL1,2] (1 and 2) and [CuL3′,4′]2 (3 and 4)) using salan ligands, N,Nʹ-dimethyl-N,Nʹ-bis-(2-hydroxy-3-X-5-Y-6-Z-benzyl)˗1,2-diaminoethane (H2L1, X = iPr, Y = Cl, Z = Me; H2L2, X = OCH3, Y = allyl, Z = H) and N,Nʹ-bis-(2-hydroxy-3-X–5-Y-6-Z-benzyl)-1,2-diaminopropane (H2L3, X = iPr, Y= Cl, Z = Me; H2L4, X = Y = CH3, Z = H), have been discussed. Molecular structures of 1 and 3 have been determined by X‒ray crystallography. An unprecedented ligand transformation occurs in the case of 3 and 4, leading to the formation of phenolato bridged Cu(II) dimeric complexes, [CuL3′,4′]2. The organic transformation in the ligand has been mechanistically elucidated to be Cu(II) catalysed. This unusual chemistry of 3 and 4 has been compared with NiII, FeIII and MoVI complexes (5‒7) with similar ligand environment. The anomaly in ligand structure was however not observed in the case of other transition metal complexes (5‒7). The superoxide dismutase (SOD) activity of the Cu(II) complexes (1‒3) has also been investigated; the activity follows the order 3 > 1 > 2. Due to the deliquescent nature of 4, its SOD activity could not be evaluated.
Chapter 7: In this chapter a brief resume of the work embodied in the thesis and concluding remarks are stated. The scope for future research work has also been discussed.