Chemistry of Oxomolybdenum Complexes with ON- and ONO- Donor Ligands

Abstract

Chapter 1: In this chapter the scope of the present investigation is delineated briefly along with the aim of the work.
Chapter 2: Reaction of benzoylhydrazone of 2-hydroxybenzaldehyde (H2L) with [MoO2(acac)2] proceeds smoothly in refluxing ethanol to afford an orange complex [MoO2L(C2H5OH)] (1). The substrate binding capacity of complex (1) has been demonstrated by the formation and isolation of two mononuclear [MoO2L(Q)] and one dinuclear [(MoO2L)2(Q)] mixed-ligand oxomolybdenum complexes. All the complexes have been characterized by elemental analysis, electrochemical and spectroscopic (IR, UV–Vis and NMR) measurements. Molecular structures of all the oxomolybdenum(VI) complexes (1, 2a, 2b and 3) have been determined by X-ray crystallography. The complexes have been screened for their antibacterial activity against Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa. The minimum inhibitory concentration of these complexes and antibacterial activity indicates the compound 2a and 2b as the potential lead molecule for drug designing.
Chapter 3: Reaction of the salicyloylhydrazone of 2-hydroxy-1-naphthaldehyde (H2L1), anthranylhydrazone of 2-hydroxy-1-naphthaldehyde (H2L2), benzoylhydrazone of 2-hydroxy-1-acetonaphthone (H2L3) and anthranylhydrazone of 2-hydroxy-1-acetonaphthone (H2L4; general abbreviation H2L) with [MoO2(acac)2] afforded a series of 5- and 6- coordinate Mo(VI) complexes of the type [MoO2L1–2(ROH)] [where R = C2H5 (1) and CH3 (2)], and [MoO2L3–4] (3 and 4). The substrate binding capacity of 1 has been demonstrated by the formation of one mononuclear mixed-ligand dioxomolybdenum complex [MoO2L1(Q)] . Molecular structure of all the complexes (1, 1a, 2, 3 and 4) is determined by X-ray crystallography, demonstrating the dibasic tridentate behavior of ligands. All the complexes have been characterized by elemental analysis, electrochemical and spectroscopic (IR, UV–Vis and
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NMR) measurements. The complexes have been screened for their antibacterial activity against Escherichia coli, Bacillus subtilis, Proteus vulgaris and Klebsiella pneumoniae. The minimum inhibitory concentration of these complexes and antibacterial activity indicates 1 and 1a as the potential lead molecule for drug designing. Catalytic potential of these complexes was tested for the oxidation of benzoin using 30% aqueous H2O2 as an oxidant in methanol. At least four reaction products benzoic acid, benzaldehyde-dimethylacetal, methylbenzoate and benzil were obtained with the 95-99% conversion under optimized reaction conditions. Oxidative bromination of salicylaldehyde, a functional mimic of haloperoxidases, in aqueous H2O2/KBr in the presence of HClO4 at room temperature has also been carried out successfully.
Chapter 4: Report of synthesis and characterization of two novel dimeric [(MoVIO2)2L] (1) and tetrameric [2(-O)2]·C2H5OH (2) dioxomolybdenum(VI) complexes with N,N'-disalicyloylhydrazine (H2L), which is formed by the self combination of salicyloyl hydrazide. Both the complex was characterized by various spectroscopic techniques (IR, UV–Vis and NMR) and also by electrochemical study. The molecular structures of both the complexes have been confirmed by X-ray crystallography. All these studies indicate that the N,N'-disalicyloylhydrazine (H2L) has the normal tendency to form both dimeric and tetrameric complexes coordinated through the dianionic tridentate manner.
Chapter 5: Two novel dioxomolybbdenum(VI) complexes containing the MoO22+ motif are reported where unexpected coordination due to ligand rearrangement through metal mediated interligand C–C bond formation is observed. The ligand transformations are probably initiated by molybdenum assisted C–C bond formation in the reaction medium. The ligands (H2L1–2) are tetradentate C–C coupled O2N2– donor systems formed in situ during the synthesis of the complexes by the reaction of bis(acetylacetonato)dioxomolybdenum(VI) with Schiff base ligands of 2-aminophenol with 2-pyridine carboxaldehyde (HL1) and 2-quinolinecarboxaldehyde (HL2). The reported dioxomolybdenum(VI) complexes [MoO2L1] (1) and [MoO2L2] (2) coordinated with the O2N2– donor rearranged ligand are expected to have better stability of the molybdenum in +6 oxidation state than the corresponding ON2–donor ligand precursor. Both the complexes are fully characterized by several physicochemical techniques and the novel structural features through single crystal X-ray crystallography.
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Chapter 6: In this chapter we present a detailed account of the synthesis, structure, spectroscopic, electrochemical properties and study of biological activity of some oxomolybdenum(VI) complexes with special reference to their H–bonded molecular and supramolecular structures. Reaction of bis(acetylacetonato)dioxomolybdenum(VI) with three different hydrazides (isonicotinoyl hydrazide, anthraniloyl hydrazide and 4-nitrobenzoyl hydrazide) afforded two di-oxomolybdenum(VI) complexes and one mono-oxomolybdenum(VI) complex (where L = Intermediate in situ ligand formed by the reaction between acetyl acetone and the corresponding acid hydrazide, and O–N = 4-nitrobenzoylhydrazide). All the complexes have been characterized by elemental analysis, electrochemical and spectroscopic (IR, UV–Vis and NMR) measurements. Molecular structures of all the complexes (1, 2 and 3) have been determined by X-ray crystallography. The complexes have been screened for their antibacterial activity against Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa. The Minimum inhibitory concentration of these complexes and antibacterial activity indicates 1 as the potential lead molecule for drug designing.