Characterization of Several Metalloporphyrins in Unusual Oxidation States. The Effect of Axial and Equatorial Ligands

The effect of axial and equatorial ligands on the generation of unusual oxidation states in metalloporphyrins is discussed. Selected examples have been taken from the literature. These include the generation of Ni(III) and Ru(III) porphyrins from Ni(II) and Ru(II) complexes containing specific axial and equatorial ligands as well as the generatoin of a Cu(I) metalloporphyrin dianion which is produced upon the overall three-electron reduction of Cu(II) tetracyanoporphyrin. Special emphasis is placed on the oxidation and reduction of σ bonded iron phenyl porphyrins. These complexes, which are stable as Fe(III), may be oxidized by a single electron to yield unstable compounds characterized as containing a great deal of Fe(IV) character, or reduced by a single electron to produce stable species which resemble, in part, radical anions of Fe(III). This singly deduced species may be described by a resonance equilibria between an Fe(III) porphyrin anion radical and an Fe(II) porphyrin anion. Likewise, the singly oxidized complex may be described by a resonance equilibria between an Fe(IV) porphyrin cation and an Fe(III) cation radical.     

苯丙氨酸铁卟啉配合物的合成及其催化环氧化性质

文章合成了两个新的手性卟啉配合物-尾式L（D）-苯丙氨酸铁Hh啉,并通过紫外光谱和质谱对其结构进行了表征。利用这两个化合物进行了苯乙烯的催化环氧化研究,分别考察了不同溶剂和不同轴向配体的影响。实验结果显示尾式L（D）-苯丙氨酸铁卟啉催化苯乙烯氧化的产物不具有对映体选择性。在不同溶剂中的环氧化物产率：乙腈〉二氯甲烷〉甲醇。在不同轴向配体作用下的产率为：吡啶〉4．硝基咪唑〉咪唑。     

Selective molecular oxygen transport through a cellulose acetate membrane containing an electron-poor iron(II) porphyrin complexes

Molecular oxygen diffusion in the cellulose acetate membranes containing the 5,10,15, 20-tetrakis(pentafluorophenyl)-21H,23H-porphine iron(II) was studied. Both the permeability coefficient and the separation factor for oxygen in the membrane containing the iron(II) porphyrin complex were increased with decreasing the upstream gas pressure which correspond to a dual-mode oxygen transport. The effects of the axial ligands of the iron(II) porphyrin on oxygen permeation was also examined in the same cellulose acetate membrane. The fluoride and 2-methyl imidazole ligands coordination to the iron(II) porphyrin induce to increase the oxygen permeability coefficient and the value of ideal separation factor.     

Peculiar sandwich-like π–π interaction regulating the nonplanarity of the model heme crystals

X-ray crystallographic analysis of bis(pyridine N-oxide) complexes of iron(III) porphyrinates has revealed that the two pyridine rings of the axial ligands correctly sandwich the porphyrin ring to induce the deformation of commonly observed S₄ saddled porphyrin ring.     

Photokatalytische Aktivierung von molekularem Sauerstoff mittels Eisen(III)porphyrin‐Komplexen

Photochemical charge transfer excitation of tetra‐phenyl(porphyrinato)iron(III) complexes yields tetraphenyl) (porphyrinato)iron(II) which is able to coordinate molecular oxygen under formation of oxo‐[tetraphenyl(porphyrinato)]‐ iron(IV). Based on this photochemical reaction pathway photocatalytic oxygenation of α‐pinene and other alkenes can be initiated. Iron(III) complexes of tetramesitylporphyrin, tetrakis‐(pentafluorophenyl)porphyrin, octa‐β‐bromo‐tetrakis‐(pentafluorophenyl)porphyrin, and octa‐β‐chloro‐tetrakis‐(pentafluorophenyl)porphyrin were investigated photochemically with the aim to improve the low photochemical efficiency of tetraphenyl(porphyrinato)iron(III). The influence of substituents on the porphyrin ligand on the photochemical behavior of the corresponding iron(III) complexes is measured mainly by means of temperature dependent UV/Vis spectroscopy. Both, the yield of oxygenation products formed photocatalytically with α‐pinene and the product distribution (allylic alcohols versus epoxide) depend on the design of the porphyrin ligands coordinated with iron(III).     

Electronic structure and reactivity of three-coordinate iron complexes

[Reaction: see text]. The identity and oxidation state of the metal in a coordination compound are typically thought to be the most important determinants of its reactivity. However, the coordination number (the number of bonds to the metal) can be equally influential. This Account describes iron complexes with a coordination number of only three, which differ greatly from iron complexes with octahedral (six-coordinate) geometries with respect to their magnetism, electronic structure, preference for ligands, and reactivity. Three-coordinate complexes with a trigonal-planar geometry are accessible using bulky, anionic, bidentate ligands (beta-diketiminates) that steer a monodentate ligand into the plane of their two nitrogen donors. This strategy has led to a variety of three-coordinate iron complexes in which iron is in the +1, +2, and +3 oxidation states. Systematic studies on the electronic structures of these complexes have been useful in interpreting their properties. The iron ions are generally high spin, with singly occupied orbitals available for pi interactions with ligands. Trends in sigma-bonding show that iron(II) complexes favor electronegative ligands (O, N donors) over electropositive ligands (hydride). The combination of electrostatic sigma-bonding and the availability of pi-interactions stabilizes iron(II) fluoride and oxo complexes. The same factors destabilize iron(II) hydride complexes, which are reactive enough to add the hydrogen atom to unsaturated organic molecules and to take part in radical reactions. Iron(I) complexes use strong pi-backbonding to transfer charge from iron into coordinated alkynes and N 2, whereas iron(III) accepts charge from a pi-donating imido ligand. Though the imidoiron(III) complex is stabilized by pi-bonding in the trigonal-planar geometry, addition of pyridine as a fourth donor weakens the pi-bonding, which enables abstraction of H atoms from hydrocarbons. The unusual bonding and reactivity patterns of three-coordinate iron compounds may lead to new catalysts for oxidation and reduction reactions and may be used by nature in transient intermediates of nitrogenase enzymes.     

Bioinspired hydrogen bond motifs in ligand design: the role of noncovalent interactions in metal ion mediated activation of dioxygen

Hydrogen bonds influence secondary coordination spheres around metal ions in many proteins. To duplicate these features of molecular architecture in synthetic systems, urea-based ligands have have been developed that create rigid organic frameworks when bonded to metal ions. These frameworks position hydro-gen bond donors proximal to metal ion(s) to form specific chem-ical microenvironments. Iron(II) and manganese(II) complexes with constrained cavities activate O(2), yielding M(III) (M(III) = Fe and Mn) complexes with terminal oxo ligands. Installation of anionic sites within the cavity assists the formation of complexes with M(II/III)-OH and M(III)-O units derived directly from water. Opening the cavity promotes M(mu-O)(2)M rhombs, as illustrated by isolation of a cobalt(III) analogue, the stability of which is promoted by the hydrogen bonds surrounding the bridging oxo ligands.     

Photodegradation of azo‐dyes in aqueous solution by polyacrylonitrile nanofiber mat‐supported metalloporphyrins

Electrospinning has been employed to fabricate uniform polyacrylonitrile and polyacrylonitrile copolymer nanofiber mats supporting metalloporphyrins (MTPP; M: Zn(II), Cu(II), Ni(II), Co(II), Fe(III) and Pd(II); TPP: meso‐tetraphenylporphyrin). The nanofiber mat‐supported metalloporphyrins are shown as efficient photocatalysts for the degradation of various azo‐dyes in aqueous solutions under visible light irradiation. The effect of transition metals on azo‐dye photodegradation has been examined. The nanofiber mat‐supported copper–porphyrin and iron–porphyrin complexes are among the most effective photocatalysts for azo‐dye degradation. Immobilization of the metalloporphyrins onto the nanofiber mats greatly facilitates the recovery and reuse of the expensive and toxic photocatalysts. Most interestingly, there are no significant degradations of the photocatalytic activities of the recycled photocatalysts. © 2012 Society of Chemical Industry     

Antibacterial Co(II) and Ni(II) Complexes of N-(2-Furanylmethylene)-2-Aminothiadiazole and Role of SO(4), NO(3), C(2)O(4) and CH(3)CO(2) anions on Biological Properties

Co(II) and Ni(II) complexes with a Schiff base, N-(2-furanylmethylene)-2-aminothiadiazole have been prepared and characterized by their physical, spectral and analytical data. The synthesized Schiff-bases act as tridentate ligands during the complexation reaction with Co(II) and Ni(II. metal ions. They possess the composition [M(L)(2)]X(n) (where M=Co(II) or Ni(II), L=, X=NO(3) (-), SO(4) (2-), C(2)O(4) (2-) or CH(3)CO(2) (-) and n=1 or 2) and show an octahedral geometry. In order to evaluate the effect of anions upon chelation, the Schiff-base and its complexes have been screened for antibacterial activity against bacterial strains e.g., Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa.     

Porphyrins and metalloporphyrins: potential hypoxic agents

Synthetic water-soluble porphyrins and their metalloporphyrin derivatives with Co(III), Cu(II), Ru(II) and Pt(II), containing various functional groups within the meso-positions of the porphyrin, were synthesised and evaluated as hypoxic agents, especially as cytotoxins and radiosensitisers. Cobalt complexes of the porphyrins containing positively charged methylpyridinium groups showed selective toxicity toward hypoxic Chinese Hamster Ovary (CHO) cells. The Co(III) complexes of the cationic and the anionic porphyrins are all weak radiosensitisers toward hypoxic cells, the highest sensitisation enhancement ratio (SER = 1.22, at 50 muM) being with a porphyrin complex containing a cis-arrangement of two nitro and two methylpyridinium meso-substituents. A copper complex of a tetracationic porphyrin showed slight radiosensitisation activity with an SER value of about 1.1. The other metalloporphyrins showed no hypoxic selectivity or radiosensitisation activity. In total, over 50 porphyrin free bases have been synthesised, of which half are water-soluble and have been metallated; thus, the chemistry is now in place for further development of water-soluble hypoxic agents.     

Studies on Some Biologically Cobalt(II), Copper(II) and Zinc(II) Complexes With ONO, NNO and SNO Donor Pyrazinoylhydrazine-Derived Ligands

Biologically active complexes of Co(II), Ni(II), Cu(II) and Zn(II) with novel ONO, NNO and SNO donor pyrazinoylhydrazine-derived compounds have been prepared and characterized on the basis of analytical data and various physicochemical studies. Distorted octahedral structures for all the complexes have been proposed. The synthesized ligands and their complexes have been screened for their antibacterial activity against bacterial species Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Klebsiella pneumonae. The activity data show the metal complexes to be more active than the parent free ligands against one or more bacterial species.     

Complexes with biologically active ligands. Part 9 metal complexes of 5-benzoylamino- and 5-(3-nitrobenzoyl-amino)-1,3,4-thiadiazole-2-sulfonamide as carbonic anhydrase inhibitors

Complexes containing the anions of 5-benzoylamido-1,3,4-thiadiazole-2-sulfonamide and 5-(3-nitro-benzoylamido)-1,3,4-thiadiazole-2-sulfonamid as ligands, and V(IV); Cr(III); Fe(III); Co(II); Ni(II); Cu(II) and Ag(I) were synthesized and characterized by standard procedures (elemental analysis; IR, electronic, and EPR spectroscopy; TG, magnetic and conductimetric measurements). The original sulfonamides and their metal complexes are strong inhibitors of two carbonic anhydrase (CA) isozymes, CA I and II.     

Metal complexes of diisopropylthiourea: synthesis, characterization and antibacterial studies

Co(II), Cu(II), Zn(II) and Fe(III) complexes of diisopropylthiourea have been synthesized and characterized by elemental analyses, molar conductivity, magnetic susceptibility, FTIR and electronic spectroscopy. The compounds are non-electrolytes in solution and spectroscopic data of the complexes are consistent with 4-coordinate geometry for the metal(II) complexes and six coordinate octahedral for Fe(III) complex. The complexes were screened for their antibacterial activities against six bacteria: Escherichia coli, Pseudomonas auriginosa, Klebsiella pneumoniae, Bacillus cereus, Staphylococcus aureus and Bacillus pumilus. The complexes showed varied antibacterial activities and their minimum inhibitory concentrations (MICs) were determined.     

The Influence of Structural Parameters on the Reactivity of Model Complexes for Compound II: A Mini Review

The present brief review aims at elucidation of the parameters affecting the properties and reactivity of high valent iron(IV) oxo porphyrin complexes, being models of compound II reactive intermediate known from biochemistry of cytochromes and peroxidases. The stress is put on the influence of the axial ligand and porphyrin ring substituents, with special attention on implications for their catalytic activity.     

Fe(III) and Co(III) centers with carboxamido nitrogen and modified sulfur coordination: lessons learned from nitrile hydratase

Nitrile hydratase (NHase) is a non-heme Fe(III) or non-corrinoid Co(III) metalloenzyme with an unprecedented coordination sphere comprising deprotonated carboxamido nitrogens and modified Cys-S (-SO(-) and -SO(2)(-)) sulfurs. We have synthesized model complexes derived from designed ligands that contain these donor groups. The model complexes mimic almost all the intrinsic properties of the unique M(III) (M = Fe, Co) active site of NHase. Even a functional Co(III) model has been synthesized that hydrolyzes nitriles catalytically at pH close to the optimum pH of the enzyme. Our studies have provided insight into how the unusual donor atoms dictate the overall properties of the biological M(III) sites.     

Synthesis, Characterization and Biological Evaluation of Co(II), Cu(II), Ni(II) and Zn(II) Complexes With Cephradine

Some Co(II), Cu(II), Ni(II) and Zn(II) complexes of antibacterial drug cephradine have been prepared and characterized by their physical, spectral and analytical data. Cephradine acts as bidentate and the complexes have compositions, [M(L)(2)X(2)] where [M = Co(II), Ni(II) and Zn(II), L = cephradine and X = Cl(2)] showing octahedral geometry, and [M(L)(2)] where [M = Cu(II), L = cephradine] showing square planar geometry. In order to evaluate the effect of metal ions upon chelation, eephradine and its complexes have been screened for their antibacterial activity against bacterial strains, Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa.     

Synthesis of polymer-supported metal-ion complexes and evaluation of their catalytic activities

Polymer-supported transition-metal-ion complexes of the N,N′-bis(o-hydroxy acetophenone) propylenediamine (HPPn) Schiff base were prepared by the complexation of iron(III), cobalt(II), and nickel(II) ions on a polymer-anchored N,N′-bis(5-amino-o-hydroxy acetophenone) propylenediamine Schiff base. The complexation of iron(III), cobalt(II), and nickel(II) ions on the polymer-anchored HPPn Schiff base was 83.44, 82.92, and 89.58 wt%, respectively, whereas the unsupported HPPn Schiff base showed 82.29, 81.18, and 87.29 wt % complexation of these metal ions. The iron(III) ion complexes of the HPPn Schiff base showed octahedral geometry, whereas the cobalt(II) and nickel(II) ion complexes were square planar in shape, as suggested by spectral and magnetic measurements. The thermal stability of the HPPn Schiff base increased with the complexation of metal ions, as evidenced by thermogravimetric analysis. The HPPn Schiff base showed a weight loss of 51.0 wt % at 500°C, but its iron(III), cobalt(II), and nickel(II) ion complexes showed weight losses of 27.0, 35.0, and 44.7 wt % at the same temperature. The catalytic activity of the unsupported and supported metal-ion complexes was analyzed by the study of the oxidation of phenol and epoxidation of cyclohexene in the presence of hydrogen peroxide. The supported HPPn Schiff base complexes of iron(III) ions showed a 73.0 wt % maximum conversion of phenol and 90.6 wt % epoxidation of cyclohexene, but unsupported complexes of iron(III) ions showed 63.8 wt % conversion of phenol and 83.2 wt % epoxidation of cyclohexene. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 93.1 wt % and 98.1 wt % with the supported HPPn Schiff base complexes of iron(III) ions, but it was low with the supported Schiff base complexes of cobalt(II) and nickel(II) ions. The selectivity for CTL and ECH varied with the molar ratio of the metal ions but remained unaffected by the molar ratio of hydrogen peroxide to the substrate. The energy of activation for the epoxidation of cyclohexene and oxidation of phenol with the polymer-supported Schiff base complexes of iron(III) ions was 10.0 and 12.7 kJ/mol, respectively, but it was found to be higher with the supported HPPn Schiff base complexes of cobalt(II) and nickel(II) ions and with the unsupported HPPn Schiff base complexes of iron(III), cobalt(II), and nickel(II) ions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Metal dependent control of cis-/trans-1,4 regioselectivity in 1,3-butadiene polymerization catalyzed by transition metal complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine

Fe(III), Cr(III), Fe(II), Co(II) and Ni(II) chloride complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine have been synthesized and characterized along with single crystal X-ray diffraction. These complexes, in combination with MAO, have been examined in butadiene polymerization. The catalytic activity and regioselectivity are strongly controlled by metal center and cocatalyst (MAO/Co ratio dependent in the case of Co(II) complex). The activity decreases in the order of Fe(III) > Co(II) > Cr(III) ≈ Ni (II) complexes, in consistent with the space around the metal center. Polybutadiene with different microstructure content, from high trans-1,4 units (88-95% for iron(III) and Cr(III)), medium trans-1,4 and cis-1,4 units (55% and 35%, respectively, for iron(II)) to high cis-1,4 units 79% for Co(II) and 97% for Ni(II) can be easily achieved by varying of the metal center. In addition, mechanism speculation is also presented to elucidate the dependence of catalytic behaviors on metal and cocatalyst.     

Complexes With Biologically Active Ligands. Part 2. Preparation of Copper(II) Complexes of Positively-Charged Derivatives of Aminoglutethimide

Cu(II) complexes of 1-[4-(3-ethyl-piperidine-2,6-dione)-3-yl]-phenyl-2,4,6-trisubstituted pyridinium perchlorates, containing alkyl, aryl and combinations of these two types of moieties in their molecule were synthesized and characterized by elemental analysis, spectroscopy, magnetic, thermogravimetric and conductimetric measurements. In these complexes, Cu(II) ions are in octahedral geometry with four water molecules occupying the equatorial coordination sites and the two organic ligands in deprotonated state the remaining axial ones. The donor atom of these ligands is constituted by the ionized nitrogen of the glutarimide moiety. The new derivatives possess weak inhibitory activity towards the zinc enzyme carbonic anhydrase.     

A linear trinuclear mixed oxidation state cobalt(III/II/III) complex with pyrazolate bridging ligands

A linear, trinuclear cobalt complex with pyrazolate bridges has been prepared and structurally characterised. The outer cobalt centre is low spin, octahedral cobalt(III) and is coordinated by a tetra-anionic tetradentate ligand. Two of these outer cobalt(III) complexes act as bidentate chelating ligands to the central cobalt(II) ion, which adopts a distorted, flattened, tetrahedral geometry.