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The hexadentate ligand, 2,2′-bis(salicylideneamino)azobenzene, 1 has been synthesized from 2,2′-diaminoazobenzene and salicylaldehyde in refluxing diethyl ether. Reaction of ligand 1 with Cu(II) acetate and Cu(II) perchlorate separately in methanol afforded tetradentate (N,N,N,O) Cu(II) complexes, Cu(L) & [Cu(HL)]ClO 4 respectively [where H 2 L represent the one imine moiety cleavage product of ligand 1 (H represents the dissociable amino and phenolic protons)]. These were characterized by microanalytical data and spectroscopic studies. In addition, the crystal structures of the ligand 1 and complexes Cu(L) & [Cu(HL)]ClO 4 were determined by X-ray diffraction analysis. The diffraction analysis revealed that the ligand (H 2 L) binds Cu(II) centers in (N,N,N,O) tetra dentate fashion in distorted square planer geometry. In complex [Cu(HL)]ClO 4 the apical position of copper center is weakly coordinated with one perchlorate ion. The dimeric structure of the molecule [Cu(HL)]ClO 4 is stabilized through NH 2 ···O hydrogen bonds. The fluorescence and redox property of ligand 1 and complexes Cu(L) & [Cu(HL)]ClO 4 were studied. Preliminary DFT calculations were carried out using crystallographic coordinates to understand the electronic spectra and redox properties of the ligand and complexes. The complex Cu(L) shows very good catalytic activities towards oxidation of benzyl alcohol to benzaldeyhde (under solvent-free condition) and organic thioethers to sulfoxide and sulfones using H 2 O 2 as the oxidant. [ABSTRACT FROM AUTHOR]

Two new Cu(II) complexes supported by nitrogen-rich ligands have been synthesized and characterized by absorption spectroscopy, magnetic moment, and cyclic voltammetry. Complex 1 is supported by the ligand TPMEN (N,N,N′-tris(2-pyridylmethyl)-N′-methylethylenediamine) with two amine and three pyridyl nitrogen donors; while 2 is supported by the ligand TQMEN (N,N,N′-tris(2-quinolylmethyl)-N′-methylethylenediamine) where quinoline groups replace the pyridyl groups. Replacing the pyridyl moiety with quinoline has a marked effect on the Cu(II/I) reduction couple. The complexes are capable of reducing superoxide (O 2 − ) to hydrogen peroxide (H 2 O 2 ) in the presence of a proton donor. The reaction between potassium superoxide (KO 2 ) and the Cu-complexes was monitored via absorption spectroscopy, and further probed with electrospray ionization mass spectrometry (ESI-MS). Both 1 and 2 depicted evidence of ligand oxidation in mass-spectrometry. [ABSTRACT FROM AUTHOR]

Oxidation is fundamental for many chemical processes and the search for chemoselective oxidants is relevant because most substrates have different functional groups. For unsaturated organo-heteroatom (E) substrates R 1 E(CH 2 ) n CH CR 2 H, the olefin and/or the heteroatom can be oxidized. It is known that molybdenum oxodiperoxo [MoO(O 2 ) 2 L] complexes can selectively oxidize sulfide groups in the presence of alkenes. Thus, the effects of the substituents (R 1 and R 2 ) and of the separation n between the functional groups on the chemoselectivity were investigated by methods based on the density functional theory (DFT) for sulfides (E = S). The chemoselectivity was quantified by the difference between the Gibbs energy of activation at the double bond (TS@C C) and at the heteroatom (TS@E) oxidation pathways, ΔΔ ‡ G = Δ ‡ G (TS@C C) − Δ ‡ G (TS@E). Consistent with experimental observations, this oxidation is chemoselective towards the heteroatom (E = S, Se, and PCH 3 ) for any unsaturated substrate or ancillary ligand L in the complex. For unsaturated organosulfur compounds, it is shown that an increase in the electronegativity of R 1 leads to a decrease of the chemoselectivity, which can be correlated with the atomic charge at the sulfur center. The separation n affects the chemoselectivity similarly to the electronegativity of R 1 , namely, differences between sp 2 and sp 3 carbon centers. The ancillary ligand L = OPH 3 , pyrazole, pyridine N -oxide, and Si(OH) 4 , affects the reactivity of the complex and its chemoselectivity, where L = Si(OH) 4 shows the highest reactivity and the least selectivity; however, ΔΔ ‡ G is still large enough (4.3 kcal/mol) to provide high chemoselectivity. This agrees with the experimental observations related to the oxidations by [MoO(O 2 ) 2 L] complexes supported on silica. These quantitative results and the qualitative trends and correlations can be helpful in the design of more efficient and greener Mo-based oxidants. [ABSTRACT FROM AUTHOR]

Highlights: [•] Synthesis and characterization of a new multidentate ligand and its Cu(II), Ni(II) and Co(III) complexes. [•] Centrosymmetric binuclear entities containing square-pyramidal copper(II) ions bridged through the phenoxo oxygen atoms. [•] Octahedral Ni(II) and Co(III) bis complexes. [•] The luminescence behaviour and redox properties of both the ligand and complex. [•] Catalytic activity of complex toward H2O2 induced oxidation of benzyl alcohol derivatives to carbonyl compounds. [Copyright &y& Elsevier]

Abstract: Two different methods were described for the preparation of manganese complexes with triazenido derivative ligands encapsulated in NaY zeolite. The catalytic behaviour of the heterogeneous catalysts was evaluated for styrene and cyclohexanol oxidation reactions. Encapsulation was achieved by two methods: (i) ion-exchange from an ethanol solution containing both bis(p-tolyl)triazenido ligand and manganese ions, with the ligand: Mn 3:1molar ratio (Method A) and (ii) the flexible ligand method (Method B). The heterogeneous catalysts were characterized by FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD) and chemical analyses. The results show that both preparation methods lead to effective encapsulation of the Mn{bis(p-tolyl)triazenido} (1:1) complex in the NaY zeolite framework. The heterogeneous catalysts show activity in oxidation of styrene and cyclohexanol with tert-butyl hydroperoxide (tBuOOH) as an oxygen source. The catalysts are chemo-selective in cyclohexanol oxidation, whereas in styrene oxidation reaction leads to styrene oxide and benzaldehyde. [Copyright &y& Elsevier]

Abstract: A new mixed-valence copper coordination polymer with copper–copper metal bonds in a two-dimensional network was generated from an in situ oxidation reaction route under hydrothermal conditions. The synthesis of this coordination polymer demonstrated that the novel compounds that may not be accessible using the known methods could be synthesized via an oxidation reaction route. The reaction conditions are mild enough to keep the building blocks intact during the oxidation and self-assembly process under hydrothermal conditions. [Copyright &y& Elsevier]