Complexes of dibenzoyldisulphide with metal halides. Part III. Complexes of dibenzoyldisulphide with cobalt(II), nickel(II), manganese(II), copper(II), iron(III) and chromium(III) halides

Adducts (1:1) of halides of cobalt(II), nickel(II), manganese(II), copper(II), iron(III) and chromium(III) with dibenzoyldisulphide have been isolated and characterized on the basis of elemental analysis, molar conductance, magnetic susceptibility, infrared spectra, molecular weight and thermogravimetric analysis data.     

Complexes of d(+)-biotin with Pd(II) and Pt(II)

The reactions of d(+)-biotin with K₂MX₄, where M = Pd(II) or Pt(II) and X = Cl or Br have been studied in acidic, neutral or alkaline aqueous solutions. Complexes of the type trans-M(Bio)₂X₂ have been isolated for both metals and characterized with elemental analyses, conductivity measurments, ir spectra, ¹Hnmr and ¹³Cnmr spectra. The complex of the type [Pd(Bio)Cl₂]₂ has also been isolated from DMF solutions. The results indicate that d(+)-biotin coordinates exclusively through its sulfur atom with these metals in all the complexes in the present study, in the solid state or in solution.     

Synthesis and structure of cis-dichlorobis(2-phenylazopyridine)chromium(II), an inert chromium(II) compound

Recent studies have shown 2-phenylazopyridine (Azpy) to be a useful departure from polypyridyl type ligands in coordination chemistry; frequently lower oxidation states are stabilized by this ligand. We have prepared and studied [Cr(Azpy)₂Cl₂] which is surprisingly inert for a chromium(II) complex. The compound crystallizes in the space group P2₁/c with a = 7.953(3), b = 21.189(11), c = 12.922(12) Å, β = 114.80(5)° and Z = 4. Based on 6777 reflections the structure has been refined to R = 0.030 and R_w = 0.038. The complex is six-coordinated with cis-chlorides, cis-azo and trans-pyridyl groups. The overall symmetry is close to C₂. The azo NN distances are elongated to 1.282 and 1.314 Å, significantly longer than observed in free azo groups.The magnetic moment of 2.8 BM is independent of temperature indicating an orbitally non-degenerate low-spin ground state. In acetonitrile the spectrum shows a band in the red at 1470 nm which is assigned as ligand-metal charge transfer, consistent with earlier interpretations on similar compounds. The compound is stable to air oxidation in acetonitrile or methylene chloride; cyclic voltammetry in these solvents yields potentials of 0.508 and −0.185 V, both appearing to be one electron transfers.The complex is a non-electrolyte in acetonitrile, nearly unchanged over 24 h. However, chloride ions are slowly replaced at 50 °C in this solvent by 2,2′-bipyridyl; this reaction is pseudo-first order in complex with a rate constant of 4.0 ± 0.3 × 10⁻⁷ s⁻¹. All data indicate the presence of a strong chromium-Azpy pi-interaction.     

Adriamycin Complexes of Pd(II) and Pt(II)

Perturbations of the ¹H NMR spectrum of the free base of Adriamycin in DMF solution were found when MCl₂(DMF)₂ (M = Pd or Pt) was added to the Adriamycin solutions. These perturbations were greatest for the 3' proton on the sugar ring and the effect decreased as the distance from this site increased. No changes were observed in the NMR spectrum of the rest of the molecule nor was there any color change when the metal solutions were added. This is interpreted as evidence that Adriamycin binds to these metals at the 3 ' amino group in DMF solution and that there is no reaction at the chromophore. The complexes were found to be in the fast exchange regime on the NMR time scale. As well, some products were isolated from reactions of Adriamycin with MCl₂(DMF)₂ in 20% MeOH/CH₂Cl₂ and MCl₂ in DMF solution. They were characterized by their elemental analyses, as well as by ¹H NMR and infrared spectroscopies.     

Adducts of guanine with chromium(III), iron(III) and oxovanadium(IV) chlorides

The preparation of well-defined adducts of the M(guH)(₂Cl₃ (M = Cr, Fe) and VO(guH)Cl₂ types (guH = neutral guanine), by refluxing ligand and metal chloride mixtures in ethanol-triethyl orthoformate, is reported. Characterization studies suggest that the new complexes are probably linear chain-like polymeric species, involving single bridges of bidentate guH ligands between adjacent metal ions. Bidentate bridging guH is most probably coordinated through the N(7) and N(9) imidazole nitrogens. The chloro ligands present in the adducts are exclusively terminal. Infrared evidence rules out the possibility of coordination of guanine through either of its exocyclic potential binding sites (i.e., CO oxygen and NH₂ nitrogen) [1].     

Anti-tubercular Activity of Ruthenium (II) Complexes with Polypyridines

A series of nine polypyridyl-ruthenium (II) complexes (N-ligands = 2,2′-bipyridines; 2,2′-6′,2′-terpyridines, di-alkyloxy-2,2′-6,2-bipyridine-3,3′-di-carboxylates), were tested against Mycobacterium tuberculosis (MBT). The complex (11) showed remarkable activity against MBT as compared to other complexes, (1–10). The aquo ligand of complex (11), as opposed to other chloro and acetonitrile derivatives, appears to play a key role in the antitubercular potency of this new class of metal-based compounds.     

Manganese(II), iron(II) and nickel(II) chloride complexes with monodeprotonated anionic guanine

Upon refluxing 2:1 mixtures of guanine (guH) and MnCl₂, FeCl₂ or NiCl₂ in a 7:3 (v/v) mixture of ethanol and triethyl orthoformate for 1–2 weeks, partial substitution of gu^? for Cl^? groups occurs, and solid complexes of the M(gu)Cl·2ROH (R = C₂H₅ for M = Mn; R = H for M = Fe, Ni) type are obtained. The new complexes are pentacoordinated and appear to be linear chainlike polymeric species, involving a single-bridged

_n backbone. Coordination number five is attained by the presence of one terminal chloro and two terminal ROH ligands per metal ion. Most probable binding sites of bidentate bridging gu^? are the N(7) and N(9) imidazole ring nitrogens. IR evidence rules out the possibility of coordination of gu^? through any of the exocyclic potential ligand sites (O(6) oxygen or N(2) nitrogen) [1].     

Amidino-complexes of iron(II) and (III)

Lithioamidines {R′N(Li)C(R)NR′, I; R = CH₃, R′ = C₆H₅, p-CH₃,C₆H₄} react with iron(III) chloride

in monoglyme to produce navy-blue, high spin Fe{R′NC(R)NR′}₃ complexes which are extremely air and moisture sensitive. The corresponding reaction when R = R′ = C₆H₅ produces a soluble red complex and an air-stable green complex, whereas when R = H, R′ = C₆H₅ and R = R′ = C₆H₅ and the reaction is started at ca. ?20°, red and green complexes respectively are formed. Though all the complexes are formulated Fe{R′NC(R)NR′}₃, their properties reflect association through bridging amidino-groups. Iron(II) chloride reacts with I(R = CH₃, R′ = p-CH₃C₆H₄) to form two complexes, one crimson and soluble in organic solvents, and one brown and insoluble, which are fomulated [Fe{R′NC(R)NR′}₂]_n. The iron(III) complexes failed to react with, or were decomposed by, a variety of reducing, electrophilic and nucleophilic reagents, though blue Fe{p-CH₃C₆H₄NC(CH₃)N-p-CH₃C₆H₄}₃ reacts readily with nitric oxide to form a purple addition complex from which the N-nitroso-compound p-CH₃C₆H₄NC(CH₃)N(NO)-p-CH₃C₆H₄ was obtained in high yield. Treatment of the corresponding brown iron(II) complex with nitric oxide gave no reaction.     

The reactions of octaethylporphyrin and its iron (II) and iron (III) complexes with free radicals

The reactions of dilute solutions of octaethylporphyrin and its iron (II) and iron (III) complexes with methyl, 2-cyanopropyl, t-butoxy, and benzoyloxy radicals are described. The results are summarized: (i) The reactivity of the porphyrin and its high-spin iron (II) and iron (III) complexes toward alkyl and t-butoxy radicals stands in the order: Fe^II > Fe^III ? free porphyrin. For benzoyloxy radicals the order is Fe^II > Porp > Fe^III. (ii) The exclusive path of reaction of high-spin iron (II) porphyrin with radicals is the rapid reduction of the radical and generation of an iron (III) porphyrin. The dominant path of reaction of high-spin iron (III) porphyrin with alkyl and (presumably) t-butoxy radicals is a rapid axial inner sphere reduction of the porphyrin. An axial ligand of iron is transferred to the radical. (iv) The reaction of benzoyloxy radicals with high or low-spin iron (III) porphyrins occurs primarily at the meso position. With the low-spin dipyridyl complex in pyridine the attendant reduction to iron (II) can be observed spectrally. Methyl radicals also reduce this complex by adding to the meso position. (v) The reaction of a radical with either an iron (II) or an iron (III) porphyrin results in the generation of the other valence state of iron and consequently oxidation and reduction products emanating from both iron species are obtained. (vi) No evidence for an iron (IV) is intermediate is apparent. (vii) Iron (II) porphyrins in solvents that impart either spin state are easily oxidized by diacyl peroxides. The occurrence of both axial and peripheral redox reactions with the iron complexes supports an underlying premise of a recent theory of hemeprotein reactivity. The relevance of the work to bioelectron transfer and heme catabolism is noted.     

Highly symmetrical chromium(II) bisdiketiminate complexes

Reaction of the lithium salts of N,N′-dialkyl-2-amino-4-imino-pent-2-enes, nacnac^RLi(THF) (R = CH₂Ph, Cy, nPr, iBu or S-CH(Me)Ph), with half an equivalent of CrCl₂(THF)_x yielded the homoleptic complexes (nacnac^R)₂Cr. All complexes were characterized by X-ray diffraction studies and displayed a highly symmetric, square-planar coordination around the chromium center with strong boat-like distortions of the diketiminate ligands. Reaction of nacnac^RLi(THF) (R = CH₂Ph, Cy) with one equivalent of CrCl₂(THF)_x afforded the dimeric complexes {nacnac^RCr(μ-Cl)}₂.     

Complexes of Ni(II) and Cu(II) with ofloxacin. Crystal structure of a new Cu(II) ofloxacin complex

Several coordination compounds formed between Ni(II) or Cu(II) with ofloxacin have been synthesised and characterised. According to elemental chemical analysis and FT-IR spectroscopy data, direct reaction of Ni(II) and Cu(II) salts with ofloxacin leads to formation of precipitates for which mass spectrometry demonstrates their polymeric nature. However, crystalline [Cu(oflo)2(H2O)].2H2O is formed if the reaction is carried out in the presence of ammonia. This complex crystallises in the triclinic system, space group P-1 with a=9.2887(12), b=11.2376(14), c=17.874(2) A, alpha=92.12(3), beta=95.39(3), gamma=91.71(3) degrees and Z=2. The local geometry around the Cu(II) ion is a slightly distorted square base pyramid. Electronic spectra, magnetic susceptibility measurements and EPR spectra of the synthesised complexes indicate a tetragonal environment.     

Trispyrazolylmethane piano stool complexes of iron(II) and cobalt(II)

A series of cationic trispyrazolylmethane complexes of the general form [Tm^RM(CH₃CN)₃]²⁺ (Tm = tris(pyrazolyl)methane, 1, R = 3,5-Me₂, M = Fe(II); 2, R = 3-Ph, M = Fe(II); 3, R = 3,5-Me₂, M = Co(II); 4, R = 3-Ph, M = Co(II)) with ‘piano-stool’ structures was prepared by the reaction of the N₃tripodal ligands (Tm^R)with [(CH₃CN)₆M](BF₄)₂ in a 1:1 stoichiometric ratio. Magnetic susceptibility measurements indicate that all four complexes with BF₄⁻ counter anions are paramagnetic, high-spin systems in the solid state with μ_eff at high temperatures of 5.2 (1, S = 2), 5.4 (2, S = 2), 4.9 (3, S = 3/2) and 4.6 (4, S = 3/2) BM, respectively. Comparisons of bond lengths from the metal centre to the Tm^R nitrogen donors, and from the metal centre to the acetonitrile nitrogen donors indicate that the neutral tripodal ligands appear to be more weakly coordinated to the metal centre than are the acetonitrile ligands. Reactions of these tripodal complexes with bidentate phosphine ligands, such as 1,2-diphosphinoethane or 1,2-bis(diallylphosphino)ethane leads to displacement of the tripodal ligand, or to the formation of more thermally stable bis-ligand complexes M(Tm^R)₂ (R = 3,5-dimethyl).     

Potentiometric study of vitamin D3 complexes with manganese(II), iron(II), iron(III) and zinc(II) in water-ethanol medium.

Vitamin D3 (LH) complexes with manganese(II), iron(II), iron(III) and zinc(II) were identified in water-ethanol medium (30/70). Their stability constants were determined at 298 K and at a constant ionic strength of 0.100 M using potentiometric methods. The computerisation of the experimental data showed the presence of ML (M = metal, L = deprotonated vitamin D3) and ML2 species in all cases; in addition, the ML3 iron(III) complex was detected. The calculated overall stability constants beta for MnIIL, FeIIL, FeIIIL and ZnIIL are, respectively, in logarithms, 12.4, 16.5, 28.5 and 16.5. Under the experimental conditions, the only protonated species MLH detected was with iron(III).     

Interaction between iron(II) and hydroxamic acids: oxidation of iron(II) to iron(III) by desferrioxamine B under anaerobic conditions

Interaction between iron(II) and acetohydroxamic acid (Aha), alpha-alaninehydroxamic acid (alpha-Alaha), beta-alaninehydroxamic acid (beta-Alaha), hexanedioic acid bis(3-hydroxycarbamoyl-methyl)amide (Dha) or desferrioxamine B (DFB) under anaerobic conditions was studied by pH-metric and UV-Visible spectrophotometric methods. The stability constants of complexes formed with Aha, alpha-Alaha, beta-Alaha and Dha were calculated and turned out to be much lower than those of the corresponding iron(II) complexes. Stability constants of the iron(II)-hydroxamate complexes are compared with those of other divalent 3d-block metal ions and the Irving-Williams series of stabilities was found to be observed. Above pH 4, in the reactions between iron(II) and desferrioxamine B, the oxidation of the metal ion to iron(III) by the ligand was found. The overall reaction that resulted in the formation of the tris-hydroxamato complex [Fe(HDFB)]+ and monoamide derivative of DFB at pH 6 is: 2Fe2+ + 3H4DFB+ = 2[Fe(HDFB)]+ + H3DFB-monoamide+ + H2O + 4H+. Based on these results, the conclusion is that desferrioxamine B can uptake iron in iron(III) form under anaerobic conditions.     

Selective addressing of heteroditopic ligands by iron(II) and platinum(II)

The heteroditopic ligand 4′-(4,7,10-trioxadec-1-yn-10-yl)-2,2′:6′,2″-terpyridine, 2, contains an N,N′,N″-donor metal-binding domain that recognizes iron(II), and a terminal alkyne site that selectively couples to platinum(II). This selectivity has been used to investigate routes to the formation of heterometallic systems. The single crystal structures of ligand 2 and the complex [Fe(2)₂][PF₆]₂ are reported.     

Syntheses, Characterization, and Antitumor Activities of Platinum(II) and Palladium(II) Complexes with Sugar-Conjugated Triazole Ligands

Four platinum(II) and palladium(II) complexes with sugar-conjugated bipyridine-type triazole ligands, [Pt(II) Cl(2) (AcGlc-pyta)] (3), [Pd(II) Cl(2) (AcGlc-pyta)] (4), [Pt(II) Cl(2) (Glc-pyta)] (5), and [Pd(II) Cl(2) (Glc-pyta)] (6), were prepared and characterized by mass spectrometry, elemental analysis, (1) H- and (13) C-NMR, IR as well as UV/VIS spectroscopy, where AcGlc-pyta and Glc-pyta denote 2-[4-(pyridin-2-yl)-1H-1,2,3-triazol-1-yl]ethyl 2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside (1) and 2-[4-(pyridin-2-yl)-1H-1,2,3-triazol-1-yl]ethyl β-D-glucopyranoside (2), respectively. The solid-state structure of complex 6 was determined by single-crystal X-ray-diffraction analysis. These complexes exhibited in vitro cytotoxicity against human cervix tumor cells (HeLa) though weaker than that of cisplatin.     

The kinetics of the reaction of nitrogen dioxide with iron(II)- and iron(III) cytochrome c

The reactions of NO₂ with both oxidized and reduced cytochrome c at pH 7.2 and 7.4, respectively, and with N-acetyltyrosine amide and N-acetyltryptophan amide at pH 7.3 were studied by pulse radiolysis at 23 °C. NO₂ oxidizes N-acetyltyrosine amide and N-acetyltryptophan amide with rate constants of (3.1±0.3)×10⁵ and (1.1±0.1)×10⁶ M⁻¹ s⁻¹, respectively. With iron(III)cytochrome c, the reaction involves only its amino acids, because no changes in the visible spectrum of cytochrome c are observed. The second-order rate constant is (5.8±0.7)×10⁶ M⁻¹ s⁻¹ at pH 7.2. NO₂ oxidizes iron(II)cytochrome c with a second-order rate constant of (6.6±0.5)×10⁷ M⁻¹ s⁻¹ at pH 7.4; formation of iron(III)cytochrome c is quantitative. Based on these rate constants, we propose that the reaction with iron(II)cytochrome c proceeds via a mechanism in which 90% of NO₂ oxidizes the iron center directly—most probably via reaction at the solvent-accessible heme edge—whereas 10% oxidizes the amino acid residues to the corresponding radicals, which, in turn, oxidize iron(II). Iron(II)cytochrome c is also oxidized by peroxynitrite in the presence of CO₂ to iron(III)cytochrome c, with a yield of ~60% relative to peroxynitrite. Our results indicate that, in vivo, NO₂ will attack preferentially the reduced form of cytochrome c; protein damage is expected to be marginal, the consequence of formation of amino acid radicals on iron(III)cytochrome c.     

Sod-Like Activity Studies of Cytokinin-Copper(II) Complexes

Using the pulse radiolysis technique it was shown that copper(II) complexes of kinetin and 6-benzylaminopurine (6-BAP) catalyze O^?₂ dismutation very efficiently at physiological pH. The ‘turnover’ rate constants at pH 7 were determined to be (1.5 ± 0.3) × 10⁹ and (2.2 ± 0.4) × 10⁹ M^?1 s^?1for 6-BAP and kinetin, respectively. The system was studied at pH 3–10 in the case of 6-BAP, and the results show that this complex catalyzes also HO₂ dismutation efficiently.