Article

Catalytic oxidation of organic sulfides by new Iron-Chloro Schiff base complexes: the effect of methoxy substitution and ligand isomerism on the electronic, electrochemical and catalytic performance of the complexes

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Abstract

Four new Fe(III)-Chloro Schiff base complexes were synthesized and characterized. The N2O2 type tetradentate Schiff base ligands were synthesized from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with salicylaldehyde (H2L¹), 3-methoxysalicylaldehyde (H2L²), 4-methoxysalicylaldehyde (H2L³) and 5-methoxysalicylaldehyde (H2L⁴). The corresponding iron-chloro complexes with the general formula [Fe(Lⁿ)Cl] (n=1–4 for complexes (1–4)) were characterized by FTIR and UV-Vis spectroscopy and elemental analysis. Crystal structure of (1) was obtained by single-crystal X-ray crystallography. Cyclic voltammetry was used to study the electrochemistry of the complexes. The complexes were used as catalysts for the selective oxidation of organic sulfide compounds to sulfoxides. High catalytic performance and selectivity were obtained. The spectroscopic, electrochemical and catalytic data are discussed based on the electronic, steric and electrochemical properties of the complexes.

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... Metal complexes of several transition and some rare earth metal ions in their existing oxidation states with Schiff base moieties as well as with other lone pair donor moieties have/had been developed and then applied for their therapeutic explorations in diabetes, tuberculosis, HIV, etc. [10][11][12][13][14][15][16]. Schiff base metal complexes are also the molecule of interest for those researchers who are searching potent material for catalysis, photovoltaic activity, chemosensor activity, nanomaterial syntheses and other emerging field of human wellness research [17][18][19][20][21][22][23][24]. ...
... The UVvisible spectrum of Fe(III) complex shows absorption band at 718 and 565 nm, which is assigned to the 6 A1→ 4 T1 and 6 A1→ 5 T1 transitions, respectively and additional band at 458 and 362 nm may be recognized as 6 A1→ 5 T2 and charge transfer (L→M) transition, respectively for Fe(III) complex. These transitions are favourable to distorted octahedral Fe(III) complexes [17,45,46]. The Cr(III) complex shows three absorption bands at 638, 450 and 324 nm which are assigned to 4 T1→ 4 T2, 4 T1→ 4 A2 and 4 T1→ 4 T2 transitions, respectively, characteristics of octahedral Cr(III) complexes with distortion [36,45,47]. ...
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Fe(III) and Mn(III) complexes with salen possessing appended ligands, [Fe(salen)Cl] · CH3CN(1) and [Mn(salen)(SCN)CH3OH]·CH3CN(2) [salen=N, N′‐bis(2‐hydroxylphenyl)‐o‐phenylene‐diamine], have been synthesized, and their crystal structures have been determined by X‐ray diffraction analyses. The complex (1) belong to triclinic system with space group P‐1, its structural unit has Fe(III)N2O2Cl configuration with distorted quadrangle pyramid geometry. The complex (2) belong to monoclinic system with space group P2(1)/c, its structural unit has MnN3O3 configuration with distorted octahedron geometry.
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A series of new tridentate Schiff base ligands derived from the condensation of 4,5-dinitro-1,2-phenylenediamine and various salicylaldehyde derivatives was synthesized and characterized by common spectroscopic and analytical methods. Oxidovanadium(IV) complexes of tetradentate Schiff base ligands derived from the condensation of this diamine and salicylaldehyde derivatives were also synthesized by template method and were characterized. The crystal structures of a tridentate ligand, HL2, and one of the complexes, VOLig2, were determined by X-ray crystallography. HL2 crystallizes in triclinic space group P1¯, while the VOLig2 (which crystallizes as the DMF solvate) in monoclinic space group P21/n with two [VOLig2] DMF symmetry-independent units per asymmetric part of the unit cell. The electrochemical properties of these complexes were studied by cyclic voltammetry which shows quasi-reversible VIV/VV redox process. The new complexes are also used as catalysts for the selective oxidation of cyclooctene with tert-butylhydroperoxide (TBHP) and H2O2 in acetonitrile. High catalytic activities were observed and excellent selectivity was found for the epoxidation of cyclooctene.
Article
A series of chiral Schiff bases (L1–L5) with different substituents in the salicylidenyl unit were prepared from condensation of 3-aryl-5-tert-butylsalicylaldehyde derivatives and optically active amino alcohols. Bromination of 3-phenyl-5-tert-butylsalicylaldehyde gave an unexpected product 3-(4-bromophenyl)-5-bromosalicylaldehyde, from which the corresponding Schiff base ligands L6 and L7, derived from (S)-valinol and (S)-tert-leucinol, respectively, were prepared. Ligands L1–L7 were applied to the vanadium-catalyzed asymmetric oxidation of aryl methyl sulfides. Under the optimal conditions, the oxidation of the thioanisole with H2O2 as oxidant in CH2Cl2 catalyzed by VO(acac)2-L1–L7 gives good yields (74–83%) with moderate enantioselectivity (58–77% ee). Ligand L7, containing a 4-bromophenyl group on the 3-position and a Br atom on the 5-position of the salicylidenyl moiety, displays an 80–90% ee for vanadium-catalyzed oxidation of methyl 4-bromophenyl sulfide and methyl 2-naphthyl sulfide. Copyright © 2008 John Wiley & Sons, Ltd.
Article
[Iron(III)–salen] complexes (salen=N,N′bis(salicylidene)ethylenediaminato) efficiently catalyze the H2O2 oxidation of organic sulfides and sulfoxides. The spectrophotometric kinetic studies show that these reactions follow Michaelis–Menten kinetics. The rate of the reaction is highly sensitive to the nature of the substituent present in the aryl moiety of ArSMe or ArS(O)Me and phenolic moiety of salen ligand. The plot of log k values of p-XC6H4SMe and p-XC6H4S(O)Me with Hammett σ constant give the reaction constant (ρ) values in the range of −0.7 to −1.5 and −0.7 to −1.0, respectively, for different iron(III)–salen complexes But the plot of log k values with σ gives positive ρ value when we introduce substituents in the phenolic moiety of iron(III)–salen complexes. The binding of the substrates with iron(III)–salen complexes is more pronounced with the sulfoxides. The product analyses show the selective oxidation of sulfides to sulfoxides and sulfoxides to sulfones. Based on the spectral and kinetic studies the possible mechanisms have been proposed.
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Nonheme iron(IV)-oxo oxidants in enzymes: Spectroscopic properties and reactivity patterns Heme iron(IV)-oxo oxidants in enzymes: Spectroscopic properties and reactivity patterns Mechanism and function of taurine/ -ketoglutarate dioxygenase enzymes, an update Mechanism and function of cysteine dioxygenase enzymes Mechanism and function of heme peroxidase enzymes Mechanism and function of cytochrome P450 enzymes Biomimetic studies of mononuclear nonheme iron containing oxidants Biomimetic studies of mononuclear porphyrin containing oxidants Density functional calibration studies on iron-containing systems Density functional theory studies on isomerisation reactions catalyzed by cytochrome P450 enzymes Quantum mechanics/molecular mechanics studies of peroxidase enzymes Theoretical modelling of nonheme iron containing oxidants
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Mononuclear iron(II) complexes of enantiopure Py(ProOH)2 (2) and Py(ProPh2OH)2(3) ligands have been prepared with FeCl2 and Fe(OTf)2 . 2MeCN. Both ligands coordinate to the metal in a pentadentate fashion. Next to the meridional N,N',N-coordination of the ligand, additional coordination of the oxygen atoms of both hydroxyl groups to the metal is found in complexes 4-7. Complex [FeCl(2)](Cl) (4) shows an octahedral geometry as determined by X-ray diffraction and is formed as a single diastereoisomer. The solution structures of complexes 4-7 were characterized by means of UV-Vis, IR, ESI-MS, conductivity and CD measurements. The catalytic potential of these complexes in the oxidation of alkenes and sulfides in the presence of H2O2 is presented.