Aliphatic Diimines Research Articles

Monomeric and Dimeric Oxidomolybdenum(V and VI) Complexes, Cytotoxicity, and DNA Interaction Studies: Molybdenum Assisted C═N Bond Cleavage of Salophen Ligands.

Four novel dimeric bis-μ-imido bridged metal-metal bonded oxidomolybdenum(V) complexes [MoV2O2L'21-4] (1-4) (where L'1-4 are rearranged ligands formed in situ from H2L1-4) and a new mononuclear dioxidomolybdenum(VI) complex [MoVIO2L5] (5) synthesized from salen type N2O2 ligands are reported. This rare series of imido-bridged complexes (1-4) have been furnished from rearranged H3L'1-4 ligands, containing an aromatic diimine (o-phenylenediamine) "linker", where Mo assisted hydrolysis followed by -C═N bond cleavage of one of the arms of the ligand H2L1-4 took place. A monomeric molybdenum(V) intermediate species [MoVO(HL'1-4)(OEt)] (Id1-4) was generated in situ. The concomitant deprotonation and dimerization of two molybdenum(V) intermediate species (Id1-4) ultimately resulted in the formation of a bis-μ-imido bridge between the two molybdenum centers of [MoV2O2L'21-4] (1-4). The mechanism of formation of 1-4 has been discussed, and one of the rare intermediate monomeric molybdenum(V) species Id4 has been isolated in the solid state and characterized. The monomeric dioxidomolybdenum(VI) complex [MoVIO2L5] (5) was prepared from the ligand H2L5 where the aromatic "linker" was replaced by an aliphatic diimine (1,2-diaminopropane). All the ligands and complexes have been characterized by elemental analysis, IR, UV-vis spectroscopy, NMR, ESI-MS, and cyclic voltammetry, and the structural features of 1, 2, 4, and 5 have been solved by X-ray crystallography. The DNA binding and cleavage activity of 1-5 have been explored. The complexes interact with CT-DNA by the groove binding mode, and the binding constants range between 103 and 104 M-1. Fairly good photoinduced cleavage of pUC19 supercoiled plasmid DNA was exhibited by all the complexes, with 4 showing the most promising photoinduced DNA cleavage activity of ∼93%. Moreover, in vitro cytotoxic activity of all the complexes was evaluated by MTT assay, which reveals that the complexes induce cell death in MCF-7 (human breast adenocarcinoma) and HCT-15 (colon cancer) cell lines.

Electrochemical, catalytic and antimicrobial activities of N-functionalized cyclam based unsymmetrical dicompartmental binuclear nickel(II) complexes

Five binuclear nickel(II) complexes have been prepared by simple Schiff base condensation of the compound 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-l,4,8,11-tetraazacyclotetradecane (L) with appropriate aliphatic or aromatic diamine, nickel(II) perchlorate and triethylamine. All the complexes were characterized by elemental and spectral analysis. Positive ion FAB mass spectra show the presence of dinickel core in the complexes. The electronic spectra of the complexes show red shift in the d–d transition. Electrochemical studies of the complexes show two irreversible one electron reduction processes in the range of 0 to −1.4 V. The reduction potential of the complexes shifts towards anodically upon increasing chain length of the macrocyclic ring. All the nickel(II) complexes show two irreversible one electron oxidation waves in the range 0.4–1.6 V. The observed rate constant values for catalysis of the hydrolysis of 4-nitrophenyl phosphate are in the range of 1.36 × 10 −2–9.14 × 10 −2 min −1. The rate constant values for the complexes containing aliphatic diimines are found to be higher than the complexes containing aromatic diimines. Spectral, electrochemical and catalytic studies of the complexes were compared on the basis of increasing chain length of the imine compartment. All the complexes show higher antimicrobial activity than the ligand and metal salt.

Synthesis and characterization of a new series of unsymmetrical macrocyclic binuclear vanadyl(IV) complexes: Electrochemical, antimicrobial, DNA binding and cleavage studies

A new series of unsymmetrical macrocyclic binuclear bis-phenoxo bridged oxidovanadium(IV) complexes have been synthesized and characterized by elemental and spectral techniques. A cyclic voltammetric investigation of these binuclear V IVO complexes evidenced that two successive quasi-reversible one electron transfer reduction waves ( E 1 pc = −0.54 to −0.67 V, E 2 pc = −0.80 to −0.85 V) are obtained. In the positive potential region (+0.50 to +1.00 V) two quasi-reversible oxidation couples are observed for all the complexes. The first one electron oxidation is observed around ( E 1 pc ) +0.63 to +0.78 V and the second around ( E 2 pc ) +0.82 to +0.97 V. The ESR spectra of all the binuclear V IVO complexes showed a single broad-band resonance at ca. g = 1.97–2.11 with the half field signal at 1500G ( M = ±2), which suggest magnetic interactions between two V IVO ions through the phenolate bridge. DNA binding experiments show that the aromatic diimine containing macrocyclic V IVO complexes display better DNA interactions than the aliphatic diimine containing V IVO analogues. These complexes significantly promote the oxidative cleavage of supercoiled plasmid DNA under physiological conditions in the presence of H 2O 2. All the complexes show noticeable growth inhibition of some plant pathogenic fungal species and human pathogenic bacterial species.

Synthesis, electrochemical, catalytic and antimicrobial activities of novel unsymmetrical macrocyclic dicompartmental binuclear nickel(II) complexes

A series of novel unsymmetrical dicompartmental binuclear nickel(II) complexes have been prepared by simple Schiff base condensation of the compound 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-l,4,8,11-tetraazacyclotetradecane L with appropriate aliphatic or aromatic diamine, nickel(II) perchlorate and triethylamine. All the complexes were characterized by elemental and spectral analysis. Positive ion FAB mass spectra show the presence of dinickel core in the complexes. The electronic spectra of the complexes show the d–d transition in the range of 550–1040 nm. Electrochemical studies of the complexes show two irreversible one electron reduction process around E pc 1 = - 0.79 to − 1.27 V and E pc 2 = - 1.28 to − 1.43 V . The reduction potential of the binuclear nickel(II) complexes shifts towards anodically upon increasing chain length of the macrocyclic ring. All the nickel(II) complexes show two irreversible oxidation waves around 0.72 to +1.52 V. The observed rate constant values for catalysis of the hydrolysis of 4-nitrophenyl phosphate are in the range of 9.20 × 10 −3–16.81 × 10 −3 min −1. The rate constant values for the complexes containing aliphatic diimines are found to be higher than that of the complexes containing aromatic diimines. Spectral, electrochemical and catalytic studies of the complexes were compared on the basis of increasing chain length of the imine compartment. All the complexes were screened for antifungal and anti bacterial activity.

Reductive electrochemical study of Ni(II) complexes with N 2O 2 Schiff base complexes and spectroscopic characterisation of the reduced species. Reactivity towards CO

Reductive electrochemical properties of series of nickel(II) complexes with salen ligands, which have different diimine bridges and substituents in the aldehyde moiety have been studied in several solvents (CH 3CN, dmf and (CH 3) 2SO). In order to assess the relative importance of the Ni(I) and Ni(II) anion radical species, the reduced species have been characterised by combining EPR and UV–Vis spectroscopy. The results have shown that complexes with aliphatic diimine bridges are reduced to four-coordinate Ni(I) species with a B 1g (d xy ) 1 ground state, whereas those with aromatic diimine bridges are reduced to square–planar Ni(II) anion radical species that rapidly dimerise. None of the reduced species was found to bind pyridine, imidazole and triphenylphosphine, but in the presence of the stronger π-acceptor ligand CO, new Ni(I) species were formed that, and on the basis of EPR data, can be formulated as five-coordinate complexes with a B 1g (d xy ) 1 ground state, [NiL·CO] −. These new species are more stable than the parent complexes as confirmed by the more positive E 1/2 values as a consequence of the extensive π delocalisation M→CO.

Synthesis and Spectroscopic Properties of 1,2-Diiminetricarbonylrhenium( I)chloride Complexes with Aliphatic Diimines (or 1,4-Diaza-1,3-butadienes) as Ligands

Re(1,2-diimine)(CO)3Cl complexes with the aliphatic bidentate ligands diiminosuccinodinitrile (DISN), benzilbisanile (BEAN), bisacetylbisanile (BABA), and benzildiimine (BEDIM) are reported. The compounds show Re(I) to π*(diimine) metal-to-ligand charge transfer (MLCT) absorptions in the visible spectral region. The energy of these MLCT-transitions decreases in the series BABA > BEDIM > BEAN > DISN, depending on the π* acceptor properties of the coordinated diimine ligands. The maxima of these CT bands undergo a solvent-dependent shift (negative solvatochromism), which indicates a partial charge redistribution in the excited state. The compounds are not photoluminescent at room temperature and 77 K.

Low valence states of iron complexes of aliphatic and mixed aliphatic-aromatic diimine ligands

Electrochemical reductions of iron(II) diimine complexes [FeL 3 2+, where L = CH 3NC(R)C(R′) NCH 3, aliphatic diimine series with R,R′ = H,H; H,CH 3 and CH 3,CH 3 and L = C 5H 4NC(R)N(R′), mixed diimine series with R,R′ = H,CH 3 and CH 3] were investigated through polarography and cyclic voltammetry in acetonitrile, with tetraethylammonium perchlorate supporting electrolyte (0.2 M) as a function of temperature. In the 0 to −2.4 V vs. Ag/AgCl potential range two to four polarographic waves were observed for the aliphatic series. The first two waves can be described as one-electron reversible reduction processes. They indicate that low valence states iron(I) and iron(0) are stabilized in acetonitrile. In the mixed ligand series three one-electron reversible reduction waves were observed, indicating that in addition to the low valence states stabilized in the aliphatic diimine series the formal reduction state Fe(–I) is also stabilized. The stabilization of the low oxidation states is due to the electron acceptor properties of the diimine ligands, inherent to the presence of the chromophoric iron diimine group. The half-wave potential data and the stabilization of the low valence states point to the importance of analyzing both σ and π effects. The molecular electronegativity values for the series of iron diimine complexes investigated evidences a synergistic interaction between the metal-ligand σ and π bonds. Diffusion coefficients, temperature effects on the heterogeneous electron transfer step, and electrocapillary curves were obtained for these complexes. No evidence for adsorption of the complexes on mercury electrodes was found for the one-electron reversible steps. When comparing polarographic data with those obtained on platinum disk working electrodes employed in the cyclic voltammetric experiments, we observed that for the symmetric aliphatic diimine ligands the observed cathodic currents are larger than expected on the basis of the previously calculated diffusion coefficients. In addition, the reduction waves are shifted 0.14 V to more negative potentials. The symmetric aliphatic diimine complexes exhibit adsorption of the electroactive species on the surface of the platinum electrodes in this potential range.

Ligand oxidation in iron diimine complexes. V. Kinetics of the oxidation of tris[2-pyridinal-α-methyl-(methylimine)] iron(II) by cerium(IV)

At low acid concentration, e.g., <4 MH 2SO 4, the cerium(IV) oxidation of the iron(II) complex of the mixed-diimine ligand 2-pyridinal-α-methyl-(methylimine), PMM = C 5H 4NC(CH 3)NCH 3, is a very complex reaction in which ligand-oxidized iron(II) and iron(III) complexes are formed and partly dissociated, with a total consumption of 10–11 equivalents of Ce(IV) per mole of Fe(PMM) 2+ 3. The major oxidation product in ∼50% yield is Fe(PO) 3+ 3, where PO = C 5H 4NC(CHO)NCH 3. The oxisation product has the α-methyl group oxidized to an aldehyde group. At the beginning of the reaction (<25% of the total Ce(IV) comsumption) Fe(PMM) 2Po 2+ was identified as the major reaction product: Ce(IV) + Fe(PMM) 2+ 3 = Ce(III) + Fe(PMM) 3+ 3 → 0.75 Fe- (PMM) 2+ 3 + 0.25 Fe(PMM) 2PO 2+. At this stage the kinetics of the reaction was analyzed by two potentiometric techniques. From experiments of addition of Fe(PMM) 3+ 3, prepared in 5 M H 2SO 4, to Fe(PMM) 2+ 3, to a final 1 M H 2SO 4 concentration, the variation of the potential of the Fe(PMM) 3+ 3/Fe(PMM) 2+ 3 couple is recorded with time. This variation is associated with the rate of disproportionation of Fe(PMM) 3+ 3 yielding Fe(PMM) 2PO 2+ and the original iron(II) complex. the rate law from these experiments is -d[Fe(PMM) 3+ 3]/dt = k[Fe(PMM) 3+ 3] 1.5. From automatic titration experiments, in which CE(IV) is added to Fe(PMM) 2+ 3 solutions at constant rate (ϱ), at high Fe(PMM) 3+ 3 concentration, the rate law is ϱ = k′[Fe(PMM) 3+ 3]. A mechanism, similar to that proposed for the oxidation of the aliphatic diimine complexes, is proposed. The first step is the formation of Fe(PMM) 3+ 3 and Ce(III) with an equilibrium constant of 4.4 × 10 7. The iron(III) complex undergoes an intramolecular reduction to the iron(II) state with concomitant radical formation at the ligand, in a step assisted by solvent water and retarded by acid. Further oxidation of the iron(II) complex-ligand-radical by Fe(PMM) 3+ 3 to the final production of Fe(PMM) 2PO 2+ leads to the derivation on the following rate law, (ϱ) - (d[Fe(PMM) 3+ 3]/dt) = (3k 3K 7[Fe(PMM) 3+ 3] 2)/ (k 4 + k 7 [Fe(PMM) 3+ 3]), which at high [Fe(PMM) 3+ 3] (automatic titrations) reduces to a first order reaction [Fe(PMM) 3+ 3] with k 3 = 0.02 s -1. Analysis of the potential variation experiments with time (low [Fe(PMM) 3+ 3]) with the whole kinetic expression above leads to k 3 = 0.02 s 1-.

Cyclic voltammetry of iron diimine complexes in acetonitrile

The electrochemical behavior of iron diimine complexes, (H3C−N=C(R)−C(R′)=N−CH3)3Fe(II) (R, R′=H,H;H, CH3; CH3, CH3), and (C5H4N−C(R1)=N(R2))3Fe(II) (R1, R2=H, CH3; CH3, CH3) on a platinum working electrode in acetonitrile is described, and compared to that of the parent aromatic complex, tris-(2,2′-bipyridine)Fe(II). One-electron reversible oxidations were found for all the compounds studied. The electrochemical reductions show 2–3 reduction waves in the potential range studied. Only for the complexes of mixed diimine ligands or 2,2′-bipyridine, a pre-adsorption wave is also observed. It is possible to stabilize low valence states with all ligands studied. A formal iron(I) state is described for the first time for all aliphatic diimine complexes, thus showing that the acceptor properties of the diimine complexes do not depend on the presence of the aromatic rings, but on the iron-diimine chromophore.

Cyclic voltammetry of iron dimine complexes in acetonitrile

The electrochemical behavior of iron diimine complexes, (H 3C−N=C(R)−C(R′)=N−CH 3) 3Fe(II) (R, R′=H,H;H, CH 3; CH 3, CH 3), and (C 5H 4N−C(R 1)=N(R 2)) 3Fe(II) (R 1, R 2=H, CH 3; CH 3, CH 3) on a platinum working electrode in acetonitrile is described, and compared to that of the parent aromatic complex, tris-(2,2′-bipyridine)Fe(II). One-electron reversible oxidations were found for all the compounds studied. The electrochemical reductions show 2–3 reduction waves in the potential range studied. Only for the complexes of mixed diimine ligands or 2,2′-bipyridine, a pre-adsorption wave is also observed. It is possible to stabilize low valence states with all ligands studied. A formal iron(I) state is described for the first time for all aliphatic diimine complexes, thus showing that the acceptor properties of the diimine complexes do not depend on the presence of the aromatic rings, but on the iron-diimine chromophore.

Glyoxal derivatives—I: Conjugated aliphatic diimines from glyoxal and aliphatic primary amines

Glyoxal reacts with primary aliphatic amines such as cyclohexylamine, n-butylamine, isopropylamine, isobutylamine and t-butylamine to give conjugated diimines whose conformations are shown to be E– E.