Vanadium(IV/V) Complexes Containing [VO]2+, [VO]3+, [VO2]+ and [VO(O2)]+ Cores with Ligands Derived from 2-Acetylpyridine andS-Benzyl- orS-Methyldithiocarbazate

Controlled Modification of Triaminoguanidine-Based μ3 Ligands in Multinuclear [VIVO]/[VVO2] Complexes and Their Catalytic Potential in the Synthesis of 2-Amino-3-cyano-4H-pyrans/4H-chromenes

Reaction of tris(2-hydroxybenzylidene)-triaminoguanidinium chloride (I·HCl) and tris(5-bromo-2-hydroxybenzylidene)-triaminoguanidinium chloride (II·HCl) with [VIVO(acac)2] (1:1 molar ratio) in refluxing methanol resulted in mononuclear [VIVO] complexes, [VIVO(H2L1')(MeOH)] (1) and [VIVO(H2L2')(MeOH)] (2), respectively, where I and II undergo intramolecular triazole ring formation. Aerial oxidation of 1 and 2 in MeOH in the presence of Cs2CO3 gave corresponding cis-[VVO2] complexes Cs[(VO2)(H2L1')] (3) and Cs[(VO2)(H2L2')] (4). However, reaction of an aerially oxidized methanolic solution of [VIVO(acac)2] with I·HCl and II·HCl in the presence of Cs2CO3 (in 1:1:1 molar ratio) gave mononuclear complexes Cs[(VO2)(H3L1)] (5) and Cs[(VO2)(H3L2)] (6) without intramolecular triazole ring formation. Similar anionic trinuclear complexes Cs2[(VO2)3(L1)] (7) and Cs2[(VO2)3(L2)] (8) were isolable upon increasing the amounts of the vanadium precursor and Cs2CO3 to 3 equiv to the reaction applied for 5 and 6. Keeping the reaction mixture of 1 in MeOH under air gave [VVO(H2L1')(OMe)] (9). Structures of 3, 7, 8, and 9 were confirmed by X-ray crystal structure study. A permanent porosity in the crystalline metal-organic framework of 7 confirmed by single-crystal X-ray investigation was further verified by the BET study. Along with a suitable reaction mechanism, these synthesized compounds were explored as effective catalysts for the synthesis of biomolecules 4H-pyran/4H-chromenes.

Investigation of thiol compounds (L-cysteine, thioacetic acid and ethanethiol) with V(V) and V(IV) using combined spectroscopy and chromatography

The interactions of V(V) and L-cysteine, thioacetic acid and ethanethiol were studied in aqueous solution using chromatographic and spectral analysis. The chromatographic determination of V(V) and V(IV) species in the presence of thiols was enabled by inducing the ligand exchange reaction with EDTA as the competing ligand. Analytical setup allowed investigation of the possible redox and structural transformations of V(V) in the presence of thiols used over a wide pH range. Obtained data strongly suggest that the reduction of V(V) is proton catalyzed in case of L-cysteine and thioacetic acid. In the case of ethanethiol, the reduction did not seem to be proton dependent, as no reduction was observed above pH = 2. Thus, reduction was inhibited by the deprotonation of L-cysteine and thioacetic acid, with L-cysteine being the strongest reducing agent of V(V), followed by thioacetic acid and finally ethanethiol. Apart from structural thiol properties, the reduction reaction seems to be influenced by the aqueous V(V) speciation due to the observed nonlinear kinetics. In the case of all investigated thiols, the formation of V(V)-thioester intermediate species was an essential step for V(V) reduction. The structural properties of the V(IV)-thiol complexes were also found to be pH-dependent.

A pair of carbazate derivatives as novel Schiff base ligands: DFT and POM theory supported spectroscopic and biological evaluation

Schiff bases are mentioned as strongly important molecular scaffolds of industrial and medicinal purposes. Due to wide range applications of carbazate derivatives herein synthesis and characterization of a new Schiff base ligand, (E)-ethyl 2-(4-methoxybenzylidene)hydrazinecarboxylate and 4-(nitrobenzaldehyde)ethylcarbazate are reported. The compound was characterized on the basis of experimental and density functional theory calculations (using the B3LYP and 6-31 G(d,p)formalism combination). Among characterization techniques elemental analysis, FT-IR, UV-Vis and NMR spectroscopic evaluations were mainly employed to carry out the formulation of the compound. In addition to computational validation of characterization other significant molecular parameters were also evaluated including geometry optimization, frontier molecular orbital analysis (FMO) and Columbic interaction of different constituent atoms of the title compound. A good agreement has been found between DFT and experimental outcomes confined to prove the structure of the compound. Moreover, molecular docking and antimicrobial studies have proven the Schiff base as an effective bioactive compound.Communicated by Ramaswamy H. Sarma.

Oxidovanadium(iv) and dioxidovanadium(v) complexes of hydrazones of 2-benzoylpyridine and their catalytic applications

V^V-polymer-supported compounds, their neat analogues and the corresponding peroxido-complexes are prepared and applied as catalyst precursors for the oxidation of isoeugenol.

Complexes of cis-dioxomolybdenum(VI) and oxovanadium(IV) with a tridentate ONS donor ligand: synthesis, spectroscopic properties, X-ray crystal structure and catalytic activity

New cis-dioxomolybdenum(VI) and oxovanadium(IV) complexes of the Schiff base, derived from S-methyl dithiocarbazate and 2,3-dihydroxybenzaldehyde (H2dhsm), have been synthesized. The complexes of the type cis-[MoO2(dhsm)] (1a), cis-[MoO2(dhsm)(D)] (1b-1d) [D=neutral monodentate ligand; EtOH, pyridine (py) or imidazole (imz)], [VO(dhsm)(NN)] (2a, 2b) [NN=2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen)] and [VO(dhsm)] (2c) have been isolated, characterized by (1)H NMR, IR, UV-Vis and EPR spectral studies and investigated by cyclic voltammetry. The X-ray crystal structure of cis-[MoO2(dhsm)(EtOH)] (1b) has been determined and shows that the complex has a distorted octahedral geometry in which the H2dhsm behaves as a dianionic ONS tridentate ligand coordinating via phenoxide oxygen, hydrazinic nitrogen and thiolate sulfur. The oxomolybdenum(IV) complex [MoO(dhsm)] (1e) has obtained from dioxomolybdenum(VI) complex (1b) by oxo abstraction with PPh3. The reactivity of the complexes toward catalytic oxidation of alcohols in the presence of H2O2 and t-BuOOH as co-oxidants under solvent free conditions is reported.

Heterocyclic dithiocarbazate iron chelators: Fe coordination chemistry and biological activity

The iron coordination and biological chemistry of a series of heterocyclic dithiocarbazate Schiff base ligands is reported with regard to their activity as Fe chelators for the treatment of Fe overload and also cancer. The ligands are analogous to tridentate heterocyclic hydrazone and thiosemicarbazone chelators we have studied previously which bear NNO and NNS donor sets. The dithiocarbazate Schiff base ligands in this work also are NNS chelators and form stable low spin ferric and ferrous complexes and both have been isolated. In addition an unusual hydroxylated ligand derivative has been identified via an Fe-induced oxidation reaction. X-ray crystallographic and spectroscopic characterisation of these complexes has been carried out and also the electrochemical properties have been investigated. All Fe complexes exhibit totally reversible Fe(III/II) couples in mixed aqueous solvents at potentials higher than found in analogous thiosemicarbazone Fe complexes. The ability of the dithiocarbazate Schiff base ligands to mobilise Fe from cells and also to prevent Fe uptake from transferrin was examined and all ligands were effective in chelating intracellular Fe relative to known controls such as the clinically important Fe chelator desferrioxamine. The Schiff base ligands derived from 2-pyridinecarbaldehyde were non-toxic to SK-N-MC neuroepithelioma (cancer) cells but those derived from the ketones 2-acetylpyridine and di-2-pyridyl ketone exhibited significant antiproliferative activity.

Synthesis, structural, and biological studies of some schiff bases and their metal complexes

New bidentate or tridentate Schiff bases and their VO(II) and Co(II) complexes formed by the condensation of methyl isobutyl ketone with nicotinamide (mna)/2-amino-4-chlorophenol (map) and 2-hydroxy acetophenone with nicotinamide (han)/isoniazide (hai). Physicochemical characterization has been carried out to determine the structure of the complexes. The FAB mass and thermal data show degradation pattern of the complexes. XRD analysis reveals that all the studied complexes crystallize as tetragonal crystal system. Some of the complexes have been screened for their antimicrobial activity by the well diffusion technique using DMSO as solvent on different species of pathogenic bacteria/fungi, that is, E. coli, S. aureus, S. fecalis, A. niger, T. polysporum, and their antimicrobial potency have been discussed. It has been found that all the complexes are antimicrobially active and show higher activity than the free ligand. Metal chelation affects significantly the antimicrobial/bioactive behavior of the organic ligands.

Structural and antimicrobial studies of coordination compounds of VO(II), Co(II), Ni(II) and Cu(II) with some Schiff bases involving 2-amino-4-chlorophenol

Complexes of tailor-made ligands with life essential metal ions may be an emerging area to answer the problem of multi-drug resistance (MDR). The coordination complexes of VO(II), Co(II), Ni(II) and Cu(II) with the Schiff bases derived from 2-hydroxyacetophenone/2-chlorobenzaldehyde with 2-amino- 4-chlorophenol were synthesized and characterized by elemental analysis, molar conductance, electronic spectra, FT-IR, ESR, FAB mass, thermal and magnetic susceptibility measurements. The FAB mass and thermal data show degradation of the complexes. The ligand A (2-hydroxyacetophenone-2amino- -4-chlorophenol) behaved as tridentate and ligand B (2-chlorobenzylidene-2- -amino-4-chlorophenol) as bidentate, coordinating through O and N donors. The complexes [VO(A)(H2O)]?xH2O, [M(A)(H2O)n]?xH2O for Co and Ni, [Cu(A)(H2O)] and [VO(B)2]?xH2O, [M(B)2(H2O)n] for Co and Cu and [Ni(B)2] exhibited coordination numbers 4, 5 or 6. X-ray powder diffraction data (a = = 11.00417 ?, b = 11.706081 ? and c = 54.46780 ?) showed that [Cu(CACP)2(H2O)2], complex 8, crystallized in the orthorhombic system. The in vitro biological screening effects of the investigated compounds were tested against the bacteria Escherichia coli, Staphylococcus aureus and Streptococcus fecalis and the fungi Aspergillus niger, Trichoderma polysporum and Candida albicans by the serial dilution method. A comparative study of the MIC values of the Schiff base and their [M(B)2(H2O)2] complexes (Co(II), complex 6 and Cu(II), complex 8), indicated that the metal complexes exhibited a higher or lower antimicrobial activity than 2-chlorobenzylidene-2-amino-4-chlorophenol as the free ligand (B).

Synthesis, characterization, and structures of oxovanadium(v) complexes of Schiff bases of β-amino alcohols as tunable catalysts for the asymmetric oxidation of organic sulfides and asymmetric alkynylation of aldehydes

Oxovanadium(V) complexes and with general formula VO(L3*)(OR5) were prepared in quantitative yields in alcohol (R5OH) from reactions of VO(O-i-Pr)3 and tridentate Schiff bases of beta-amino alcohols having one or two stereogenic centers, (HO)C*(R1)(R2)C*H(R3)N[double bond, length as m-dash]CH(2-OH-3,5-R4(2)-C6H2) (H2L3*). The alkoxy OR5 ligand exchanges readily with the alcoholic molecule in the solvent. Crystal structures of and were determined to be five-coordinate square pyramidal monomers. However, 1H NMR spectra of the complexes reveal two sets of signals, indicating the presence of two isomers in solution. The two isomers are suggested to be the endo/exo pair or the monomer/dimer pair. Asymmetric oxidations of methyl phenyl sulfide catalyzed by catalyst precursors were demonstrated to afford the chiral sulfoxide in yields and ee values similar to those obtained from the in situ-formed catalytic systems of VO(acac)2 and corresponding Schiff base ligands. Complexes and are also good catalysts for asymmetric alkynyl additions to aldehydes. Structural differences between the oxovanadium complexes, for inducing high stereoselectivities in the asymmetric oxidation of organic sulfides and the asymmetric alkynyl addition to aldehydes, are rationalized.

Mixed crystals containing the dioxo complex [{Ph3SiO}2VO2]−and novel pentacoordinated oxoperoxo complex [{Ph3SiO}2VO(O2)]−: X-ray crystal structure and assessment as oxidation catalysts

[n-Bu4N][[Ph3SiO]2VO2] reacts with H2O2 to yield an oxoperoxo complex which crystallizes as a mixed-crystal compound, [P(C6H5)4][[(C6H5)3 SiO]2VO2]x[[(C6H5)3 SiO]2VO(O2)](1-x), 1(x = 0.57). It has been characterized by elemental analysis and spectroscopy (51V NMR, UV-visible and IR). The X-ray structure analysis reveals the presence of two interrelated anions: [[Ph3SiO]2VVO2]-, 1a, and [[Ph3SiO]2VVO(O2)]-, 1b with a cisoid geometry of the [VO(O2)]+ moiety. The two structures differ only slightly: anion 1a exhibits unusual tetrahedral coordination around the vanadium centre found in the precursor, whereas the geometry at the metal ion in 1b can be described as a trapezoidal pyramid. Steric constraints due to Ph3SiO- ligands and PPh4+ cations are responsible for this geometry. The reactivity of 1 in the C-C bond cleavage of 2-methylcyclohexanone under anaerobic conditions has been studied. The results suggest that peroxygen species are involved in the oxidative cleavage of C-C bonds of cycloalkanones.