Heterodinuclear Zn(II), Mg(II) or Co(III) with Na(I) Catalysts for Carbon Dioxide and Cyclohexene Oxide Ring Opening Copolymerizations

A series heterodinuclear catalysts, operating without co-catalyst, show good performances for the ring opening copolymerization (ROCOP) of cyclohexene oxide and carbon dioxide. The complexes feature a macrocyclic ligand designed to coordinate metals such as Zn(II), Mg(II) or Co(III), in a Schiff base ‘pocket’, and Na(I) in a modified crown-ether binding ‘pocket’. The 11 new catalysts are used to explore the influences of the metal combinations and ligand backbones over catalytic activity and selectivity. The highest performance catalyst features the Co(III)Na(I) combination, [N,N′-bis(3,3’-triethylene glycol salicylidene)-1,2-ethylenediamino cobalt(III) di(acetate)]sodium ( 7 ), and it shows both excellent activity and selectivity at 1 bar carbon dioxide pressure (TOF=1590 h⁻¹, >99 % polymer selectivity, 1 : 10: 4000, 100 °C), as well as high activity at higher carbon dioxide pressure (TOF=4343 h⁻¹, 20 bar, 1 : 10 : 25000). Its rate law shows a first order dependence on both catalyst and cyclohexene oxide concentrations and a zeroth order for carbon dioxide pressure, over the range 10–40 bar. These new catalysts eliminate any need for ionic or Lewis base co-catalyst and instead exploit the coordination of earth-abundant and inexpensive Na(I) adjacent to a second metal to deliver efficient catalysis. They highlight the potential for well-designed ancillary ligands and inexpensive Group 1 metals to deliver high performance heterodinuclear catalysts for carbon dioxide copolymerizations and, in future, these catalysts may also show promise in other alternating copolymerization and carbon dioxide utilizations.     

Correlating Metal Redox Potentials to Co(III)K(I) Catalyst Performances in Carbon Dioxide and Propene Oxide Ring Opening Copolymerization

Carbon dioxide copolymerization is a front-runner CO₂ utilization strategy but its viability depends on improving the catalysis. So far, catalyst structure-performance correlations have not been straightforward, limiting the ability to predict how to improve both catalytic activity and selectivity. Here, a simple measure of a catalyst ground-state parameter, metal reduction potential, directly correlates with both polymerization activity and selectivity. It is applied to compare performances of 6 new heterodinuclear Co(III)K(I) catalysts for propene oxide (PO)/CO₂ ring opening copolymerization (ROCOP) producing poly(propene carbonate) (PPC). The best catalyst shows an excellent turnover frequency of 389 h⁻¹ and high PPC selectivity of >99 % (50 °C, 20 bar, 0.025 mol% catalyst). As demonstration of its utility, neither DFT calculations nor ligand Hammett parameter analyses are viable predictors. It is proposed that the cobalt redox potential informs upon the active site electron density with a more electron rich cobalt centre showing better performances. The method may be widely applicable and is recommended to guide future catalyst discovery for other (co)polymerizations and carbon dioxide utilizations.     

Synthesis and Properties of a Novel Cycloaliphatic Epoxide

The novel cycloaliphatic epoxide 3,4‐epoxycyclohexylmethyl‐2′,3′‐epoxycyclohexyl ether ( II ) containing an unsymmetrical epoxycyclohexyl moiety linked via an ether bond, and its precursor 3‐cyclohexene‐1‐methyl‐2′‐cyclohexene ether ( I ) were synthesized. Their structure was confirmed by means of elemental analysis, FT‐IR and ¹H NMR spectroscopy. Compared with commercial epoxide ERL‐4221, the newly synthesized epoxide II shows a higher epoxy value (0.85 eq/g) and lower viscosity (86 mpa·s/25°C). The cured product, based on epoxide II and curing agent hexahydro‐4‐methylphthalic anhydride (HMPA), showed higher glass transition temperature (162°C), higher storage modulus at the glass transition region (2.95 GPa), higher crosslinking density (1.60×10^–3 mol/cm³) and a lower coefficient of thermal expansion (6.22×10^–5/°C).     

Trinuclear salphen–chromium(III)chloride complexes as catalysts for the alternating copolymerization of epoxides and cyclic anhydrides

Although the alternating copolymerization of epoxides and cyclic anhydrides is a promising route to aliphatic polyesters, improved catalysts are required to realize commercialization of this process. Herein, trinuclear chromium complexes of salicylaldimine, in conjunction with a nucleophilic cocatalyst, are demonstrated as excellent catalysts for epoxide/cyclic anhydride copolymerization, selectively affording perfectly alternating polyesters. The effect of the distance between the chromium species is investigated by varying the bridging skeleton in a series of trinuclear salphen–Cr(III)Cl complexes for obtaining different Cr–Cr distances. Trinuclear salphenCr(III)–complexes with Cr–Cr distances of approximately 7.3 Å are found to be efficient copolymerization catalysts, even at high temperatures and extremely low catalyst loadings. In particular, a high activity of 10,620 h⁻¹ is obtained for the copolymerization of cyclohexene oxide (CHO) and phthalic anhydride (PA) under a low catalyst loading (<0.01 mol%) at 100 °C. In situ infrared spectroscopy studies suggest that the activation energy of the trinuclear Cr(III)–salphen catalyst for CHO/PA copolymerization is 15 kJ mol⁻¹ lower than that of the corresponding mononuclear catalyst owing to an intramolecular synergistic effect among the metal atoms.     

Synthesis,characterization and catalytic activity of peripherally tetra‐substituted Co(II) phthalocyanines for cyclohexene oxidation

New 3,3‐diphenylpropoxyphthalonitrile (5) was obtained from 3,3‐diphenylpropanol (3) and 4‐nitrophthalonitrile (4) with K₂CO₃ in DMF at 50 °C. The novel cobalt(II) phthalocyanine complexes, tetrakis‐[2‐(1,4‐dioxa‐8‐azaspiro[4.5]dec‐8‐yl)ethoxy] phthalocyaninato cobalt(II) (2) and tetrakis‐(3,3‐diphenylpropoxy)phthalocyaninato cobalt(II) (6) were prepared by the reaction of the phthalonitrile derivatives 1 and 5 with CoCl₂ by microwave irradiation in 2‐(dimethylamino)ethanol for at 175 °C, 350 W for 7 and 10 min, respectively. These new cobalt(II)phthalocyanine complexes were characterized by spectroscopic methods (IR, UV–visible and mass spectroscopy) as well as elemental analysis. Complexes 2 and 6 are employed as catalyst for the oxidation of cyclohexene using tert‐butyl hydroperoxide (TBHP), m‐chloroperoxybenzoic acid (m‐CPBA), aerobic oxygen and hydrogen peroxide (H₂O₂) as oxidant. It is observed that both complexes can selectively oxidize cyclohexene to give 2‐cyclohexene‐1‐ol as major product, and 2‐cyclohexen‐1‐one and cyclohexene oxide as minor products. TBHP was found to be the best oxidant since minimal destruction of the catalyst, higher selectivity and conversion were observed in the products. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and structural studies of (2 E ,3 E ,6 R ,9 E ,11 E )-6-isopropenyl-3,6,10-trimethyl-5,8-dioxa-4,9-diazadodeca-3,9-diene-2,11-dione dioxime, ligand and its Mono-, homo, and heterodinuclear copper(II)/nickel(II) complexes

This article describes the synthesis of a new (2E,3E,6R,9E,11E)-6-isopropenyl-3,6,10-trimethyl-5,8-dioxa-4,9-diazadodeca-3,9-diene-2,11-dione dioxime (H₂hmdm), and its mono-, homo, and heterodinuclear copper(II)/nickel(II) complexes. Elemental analyses, stoichiometric and spectroscopic data of the metal complexes indicated that the metal ions are coordinated to the oxime and imine nitrogen atoms (C=N). The Cu(H₂hmdm), molecule coordinates to the second copper(II) ion through the oximate oxygens to afford a binuclear structure doubly bridged by the oximate groups in the cis arrangement. In the dinuclear complexes, in which the first Cu^II ion was complexed with nitrogen atoms of the oxime and imine groups, the second Cu^II ion is ligated with the 1,10-phenanthroline nitrogen atoms. Ligand and its mononuclear copper(II), homo and heterodinuclear copper(II)–nickel(II) complexes of (H₂hmdm) were characterized by elemental analyses, magnetic moments, ¹H-n.m.r. and ¹³C-n.m.r., i.r., and mass spectral studies. The data support the proposed structure of H₂hmdm and its complexes.     

Direct synthesis,spectral and magnetic properties of trans-aniono(1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7-acetato) copper(II) complexes

7-Carboxymethyl-7,16-diaza-18-crown-6 acid hydrates (LH·H₂O) and their copper(II) complexes [CuLX], (X = Cl, Br, NO₃, ClO₄ and CH₃CO₂) were obtained. The earlier X-ray investigation of the [CuLCl] complex, as well as the IR and UV-vis spectral evidence for the complexes revealed the inner chelate structure with the six-coordinated copper(II) ion embedded inside the macrocyclic ligand (deformed octahedral, 4+2, N,N, CO₂⁻,X⁻,O,O-coordination sphere) and the trans arrangement of the CO₂ and X ligands. The spectral data, the conductivity measurements and the chemical properties show the existence of the macrocyclic inclusion cation [CuL]⁺ and the formulation of the complexes as the [(CuL)⁺X⁻] inner salts. The magnetic moments of the complexes amount to 1.76–1.83 BM at room temperature and 1.3–0.92 BM at 4.2 K. These results revealed the monomeric form of the complexes with the occurrence of the intermolecular (through space) magnetic super-exchange interactions of copper(II) paramagnetic centres.     

A Study on Diflunisal: Solubility,Acid Constants and Complex Formation with Calcium(II) and Magnesium(II)

The properties of diflunisal, a widely used analgesic, were studied in physiologic solutions, 0.15 mol·dm^?3 NaCl. Solubility and protonation constants were determined and its behavior as ligand towards Ca(II) and Mg(II) was investigated. Solubility and protonation constants of diflunisal at 25 °C and 0.15 mol·dm^?3 were obtained from electromotive force measurements of galvanic cells using coulometric titrations. The experimental data yielded the solubility, s, of –log₁₀ s = 3.86 ± 0.02 and the protonation constants log₁₀ K ₁ = 11.98 ± 0.10 and log₁₀ K ₂ = 3.86 ± 0.03. Equilibria between diflunisal and Ca(II) and Mg(II) were investigated by means of electromotive force measurements and by comparing solubilities of diflunisal in the presence and absence of Ca(II) or Mg(II), respectively. Experimental data were explained by assuming the formation of 1:1 complexes for Ca(II) and Mg(II) along with evaluating the relative stability constants.     

Electrochemistry and electrochromic properties of phenanthroline-iron(II/III) complex films

New films of the iron complexes with bis((2-hydroxyphenyl)methylaminosulfonyl)bathophenanthroline(HPBP) and bis((2-aminophenyl)methylaminosulfonyl)bathophenanthroline(APBP) ligands are prepared on the electrode surfaces by electrochemical polymerization. The resulting film-coated electrode shows a well-defined reversible voltammogram corresponding to the redox reaction of the Fe(II/III) complexes and an electrochromic change from red(absorption maximum: 540 nm) to colorless. The response rate of the color change to a potential step was found to be correlated to the apparent diffusion coefficient(Dapp) for the homogeneous charge-transport process within the film. The Dapp values estimated are (3-4) × 10⁻⁹cm²s⁻¹ for the [Fe(APBP)₃] film and(1-2) × 10⁻⁸cm²s⁻² for the [Fe(HPBP)₃] film, respectively, by potential-step chronoamperometric and chronocoulometric methods. The result of electrochemical quartz crystal microbalance(EQCM) measurements⁴) and dependence of the formal potential of the metal complex of the Fe(II/III) redox couple with activity of the supporting electrolyte anion in NaClO₄ aqueous solution showed that anion, cation, and solvent move simultaneously across the polymer film/solution interface during the redox reaction. A piezoelectric admittance measurement⁴⁾ of the poly[Fe(APBP)₃] coated quartz crystal electrode showed that the viscosity of the film is affected by the oxidation state of iron.     

Synthesis,characterization, catalase functions and DNA cleavage studies of new homo and heteronuclear Schiff base copper(II) complexes

A new tetradentate diimine–dioxime ligand containing a donor set of N₄, and its homo-, heterodinuclear and homotrinuclear copper(II) complexes were prepared and characterized on the basis of their elemental analysis, FT-IR, ¹H and ¹³C NMR spectra, molar conductivity and magnetic moment measurements. The extraction ability of N,N′′-bis[1-biphenyl-2-hydroxyimino-1-ethylidene]-diethylenetriamine was also evaluated in chloroform by using several transition metal picrates such as Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Pb(II), Cd(II) and Hg(II). It has been seen that the ligand shows strong binding ability toward the copper(II) ion. Moreover, the catalytic activities of the complexes for the disproportionation of hydrogen peroxide were investigated in the presence of imidazole. The synthesized complexes display efficiency in the disproportion reactions of hydrogen peroxide, producing water and dioxygen in catalase-like activity. The interaction between these complexes and DNA has also been investigated by agarose gel electrophoresis. We found that the homo- and heterodinuclear copper complexes can cleave supercoiled pBR322 DNA to nicked and linear forms. The dinuclear complexes including phenanthroline (2–4), with H₂O₂ as a co-oxidant, exhibited the strongest cleaving activity.     

Encapsulation of a binuclear manganese(II) complex with an amino acid-based ligand in zeolite Y and its catalytic epoxidation of cyclohexene

A Schiff base ligand was synthesized by the condensation of salicylaldehyde with l-tyrosine. Interaction of this ligand with Mn(II)-exchanged zeolite Y leads to encapsulation of the ligand within the zeolite and complexation of the metal. The encapsulated complex has been characterized by spectroscopic studies and chemical analyses. This material serves as a catalyst for the oxidation of cyclohexene to cyclohexene epoxide and 2-cyclohexene-1-ol using H₂O₂ as oxidant. The reaction conditions have been optimized for solvent, temperature and amount of oxidant and catalyst. The catalyst shows high activity and selectivity toward production of cyclohexene epoxide in acetonitrile at 60 °C with [H₂O₂]/[C₆H₁₀] = 2.5 molar ratio. Comparison of the encapsulated catalyst with the corresponding homogeneous catalyst showed that the heterogeneous catalyst had higher activity and selectivity than the homogeneous catalyst.     

Effect of PDI ligand binding pattern on the electrocatalytic activity of two Ru(II) complexes for CO2 reduction

The electrochemical properties of two complexes, [Ru^II(η³-(N,N,N)-^OMePDI)Cl₂(PPh₃)]⁰ ( 1 ) and [Ru^II(η²-(C,N)-^OMePDI-H)Cl (PPh₃)₂]⁰ ( 2 ), were studied. In octahedral complex 1 , bis(imino)pyridine (PDI) is a tridentate η³-N,N,N-coordinated ligand, whereas in trigonal-bipyramidal complex 2 , the deprotonated PDI ligand adopts the unusual bidentate binding mode η²-C,N to coordinate to the central Ru(II) ion. Bulk electrolysis in two electrolyte solutions of acetonitrile (MeCN) and tetrahydrofuran (THF) suggests that complexes 1 and 2 have very different electrocatalytic CO₂ reduction activities. In MeCN solution, complex 1 can selectively electrocatalytic CO₂ reduction to CO with a Faradaic efficiency of about 50% and a turnover frequency (TOF) of 4.4 s⁻¹, whereas complex 2 can perform electrocatalytic of CO₂ reduction with a Faraday efficiency of ~22% and a TOF of 0.3 S⁻¹. The electrocatalytic CO₂ reduction selectivity and activity of the two complexes are poor when the solvent is changed to THF. Combined with the results of the density functional theory calculation, we propose that the binding pattern of the redox-active ligand ^OMePDI has a significant effect on the electrocatalytic activity for the two Ru(II)PDI complexes.     

Semi-Rigid (Aminomethyl) Piperidine-Based Pentadentate Ligands for Mn(II) Complexation

Two pentadentate ligands built on the 2-aminomethylpiperidine structure and bearing two tertiary amino and three oxygen donors (three carboxylates in the case of AMPTA and two carboxylates and one phenolate for AMPDA-HB) were developed for Mn(II) complexation. Equilibrium studies on the ligands and the Mn(II) complexes were carried out using pH potentiometry, ¹H-NMR spectroscopy and UV-vis spectrophotometry. The Mn complexes that were formed by the two ligands were more stable than the Mn complexes of other pentadentate ligands but with a lower pMn than Mn(EDTA) and Mn(CDTA) (pMn for Mn(AMPTA) = 7.89 and for Mn(AMPDA-HB) = 7.07). ¹H and ¹⁷O-NMR relaxometric studies showed that the two Mn-complexes were q = 1 with a relaxivity value of 3.3 mM⁻¹ s⁻¹ for Mn(AMPTA) and 3.4 mM⁻¹ s⁻¹ for Mn(AMPDA-HB) at 20 MHz and 298 K. Finally, the geometries of the two complexes were optimized at the DFT level, finding an octahedral coordination environment around the Mn²⁺ ion, and MD simulations were performed to monitor the distance between the Mn²⁺ ion and the oxygen of the coordinated water molecule to estimate its residence time, which was in good agreement with that determined using the ¹⁷O NMR data.     

Heterodinuclear Ruthenium(II) Complexes of the Bridging Ligand 1,6,7,12‐Tetraazaperylene with Iron(II), Cobalt(II), Nickel(II), as well as Palladium(II) and Platinum(II)

The first heterodinuclear ruthenium(II) complexes of the 1,6,7,12‐tetraazaperylene (tape) bridging ligand with iron(II), cobalt(II), and nickel(II) were synthesized and characterized. The metal coordination sphere in this complexes is filled by the tetradentate N,N′‐dimethyl‐2,11‐diaza[3.3](2,6)‐pyridinophane (L‐N₄Me₂) ligand, yielding complexes of the general formula [(L‐N₄Me₂)Ru(µ‐tape)M(L‐N₄Me₂)](ClO₄)₂(PF₆)₂ with M = Fe {[ 2 ](ClO₄)₂(PF₆)₂}, Co {[ 3 ](ClO₄)₂(PF₆)₂}, and Ni {[ 4 ](ClO₄)₂(PF₆)₂}. Furthermore, the heterodinuclear tape ruthenium(II) complexes with palladium(II)‐ and platinum(II)‐dichloride [(bpy)₂Ru(μ‐tape)PdCl₂](PF₆)₂ {[ 5 ](PF₆)₂} and [(dmbpy)₂Ru(μ‐tape)PtCl₂](PF₆)₂ {[ 6 ](PF₆)₂}, respectively were also prepared. The molecular structures of the complex cations [ 2 ]⁴⁺ and [ 4 ]⁴⁺ were discussed on the basis of the X‐ray structures of [ 2 ](ClO₄)₄ · MeCN and [ 4 ](ClO₄)₄ · MeCN. The electrochemical behavior and the UV/Vis absorption spectra of the heterodinuclear tape ruthenium(II) complexes were explored and compared with the data of the analogous mono‐ and homodinuclear ruthenium(II) complexes of the tape bridging ligand.     

Manganese(II) complexes with Bn-tpen as powerful catalysts of cyclohexene oxidation

Manganese(II) complex [(Bn-tpen)Mn^II]²⁺ activated dioxygen for oxidation of cyclohexene in acetonitrile (MeCN) and methanol (MeOH). In MeCN, ketone (2-cyclohexen-1-one), alcohol (2-cyclohexen-1-ol) and small amounts of epoxide (cyclohexene oxide) were produced in this reaction, while in MeOH only ketone was formed. In the most efficient experiment, the combination of 2.5 × 10^?4 mol% [(Bn-tpen)Mn^II]²⁺ and 4 M cyclohexene under dioxygen atmosphere (p _O2 = 1 atm) in MeCN after 24 h of reaction, gave the TON equal to 716, and the main oxidation products were ketone (196 mM) and alcohol (147 mM), whereas epoxide was formed in insignificant amounts (15 mM). The formation of [(Bn-tpen)Mn^IV=O]²⁺ and [(Bn-tpen)Mn^III–OH]²⁺ species was confirmed. The novelty of this work is the observation, that in both solvents, [(Bn-tpen)Mn^II]²⁺ complex is initially oxidized by t-BuOOH to produce Mn(III)-complex, which is reduced back by cyclohexene to [(Bn-tpen)Mn^II]²⁺, and the latter species is an active catalyst of c-C₆H₁₀ oxidation. Knowledge of the electrochemical properties of the system components may contribute to understanding the mechanisms involving participation of the active agents created in the system.     

NNNO-Heteroscorpionate nickel (II) and cobalt (II) complexes for ethylene oligomerization: the unprecedented formation of odd carbon number olefins

The unprecedented observation of odd carbon number olefins is reported during nickel- catalyzed ethylene oligomerization. Two complexes based on Co (II) and Ni (II) with novel tetradentate heteroscorpionate ligand have been synthesized and fully characterized. These complexes showed the ability to oligomerize ethylene upon activation with various organoaluminum compounds (Et₂AlCl, Et₃Al₂Cl₃, EtAlCl₂, MMAO). Ni (II) based catalytic systems were sufficiently more active (up to 1900 kg·mol (Ni)⁻¹·h⁻¹·atm⁻¹) than Co (II) analogs and have been found to be strongly dependent on the activator composition. The use of PPh₃ as an additive to catalytic systems resulted in the increase of activity up to 4,150 kg·mol (Ni)⁻¹·h⁻¹·atm⁻¹ and in the alteration of selectivity. All Ni (II) based systems activated with EtAlCl₂ produce up to 5 mol. % of odd carbon number olefins; two probable mechanisms for their formation are suggested – metathesis and β-alkyl elimination.     

Complexation en solution aqueuse des ions magnesium(II), manganese(II), nickel(II), cuivre(II) et plomb(II) avec la s-carboxymethyl-l-cysteine: Complex formation of magnesium(II), manganese(II), nickel(II), copper(II) and lead(II) with S-carboxymethyl-L-cysteine in aqueous solution

Complex formation of magnesium(II), manganese(II), nickel(II), copper(II) and lead(II) with S-carboxymethyl-L-cysteine in aqueous solution.The complex formation between Mg(II), Mn(II), Ni(II). Cu(II), Pb(II) ions and S-carboxy-methyl-l-cysteine (H₂A) has been studied by measurement of pH at 25°C and constant ionic strength (1 M NaClO₄). Although no interaction occurs with Mg(II), this work provides evidence for a variety of complexes: MnA; CuHA⁺; CuA; CuA₂^2-; NiHA⁺; NiA; NiA₂^2-; PbHA⁺; PbA et PbA(OH)^-. The overall formation constants of all these species are computed and refined. The results allow the determination of the distribution of the complexes as a function of pH; some structural features of the metal complexes in solution are indicated.     

A Pyridinium-Pyridinium Zinc(II) Porphyrin Ion Porous Organic Polymer as Efficient Heterogeneous Catalyst for Cycloaddition of Epoxides with CO2

A zinc(II)porphyrin-based ion porous organic polymer (ZnTPyPBr₄-iPOP) is successfully synthesized from newly designed pyridinium-functionalized cationic Zn-porphyrin monomer (ZnTPyPBr₄) by free radical self-polymerization, and is employed as an efficient bifunctional heterogeneous catalyst for CO₂ cycloaddition reaction with epoxides. The ZnTPyPBr₄-iPOP exhibits excellent catalytic performance and good substrate expansion in CO₂ cycloaddition reaction under solvent-free and cocatalyst-free conditions with a TOF as high as 15,500 h⁻¹ for the cycloaddition of CO₂ and epichlorohydrin. The synergistic effect of zinc(II)porphyrin as the Lewis acidic site and the Br⁻ anion as the nucleophile in ZnTPyPBr₄-iPOP responds to the high catalytic activity. Moreover, ZnTPyPBr₄-iPOP can easily be recovered and reused at least seven times without the loss of activity. This work provides a valuable approach for the synthesis of novel and efficient heterogeneous catalyst for CO₂ cycloaddition.     

X-ray structurally characterized Mo (VI), Fe (III) and Cu (II) complexes of amide-imine conjugate: (bio)catalytic and histidine recognition studies

An amide-imine conjugate, (E)-N′-((2-hydroxybenzen-1-yl) methylene)-4-methylbenzohydrazide (H₂L^PTASAL), derived from 4-methyl-benzoic acid hydrazide (PTA) and 2-hydroxybenzaldehyde is used to prepare Mo (VI), Cu (II) and Fe (III) complexes. The X-ray structurally characterized complexes have been explored as catalyst for amine assisted asymmetric ring opening (ARO) of epoxide, carbon-heteroatom cross-coupling and ethyl benzene oxidation. In addition, their catecholase like activities have thoroughly been investigated. Moreover, the Cu (II) complex selectively recognizes histidine by fluorescence spectroscopy.     

Polymer Supported Schiff Base Complexes of Iron(III), Cobalt(II) and Nickel(II) Ions and their Catalytic Activity in Oxidation of Phenol and Cyclohexene

The polymer supported transition metal complexes of N,N′‐bis (o‐hydroxy acetophenone) hydrazine (HPHZ) Schiff base were prepared by immobilization of N,N′‐bis(4‐amino‐o‐hydroxyacetophenone)hydrazine (AHPHZ) Schiff base on chloromethylated polystyrene beads of a constant degree of crosslinking and then loading iron(III), cobalt(II) and nickel(II) ions in methanol. The complexation of polymer anchored HPHZ Schiff base with iron(III), cobalt(II) and nickel(II) ions was 83.30%, 84.20% and 87.80%, respectively, whereas with unsupported HPHZ Schiff base, the complexation of these metal ions was 80.3%, 79.90% and 85.63%. The unsupported and polymer supported metal complexes were characterized for their structures using I.R, UV and elemental analysis. The iron(III) complexes of HPHZ Schiff base were octahedral in geometry, whereas cobalt(II) and nickel(II) complexes showed square planar structures as supported by UV and magnetic measurements. The thermogravimetric analysis (TGA) of HPHZ Schiff base and its metal complexes was used to analyze the variation in thermal stability of HPHZ Schiff base on complexation with metal ions. The HPHZ Schiff base showed a weight loss of 58% at 500°C, but its iron(III), cobalt(II) and nickel(II) ions complexes have shown a weight loss of 30%, 52% and 45% at same temperature. The catalytic activity of metal complexes was tested by studying the oxidation of phenol and epoxidation of cyclohexene in presence of hydrogen peroxide as an oxidant. The supported HPHZ Schiff base complexes of iron(III) ions showed 64.0% conversion for phenol and 81.3% conversion for cyclohexene at a molar ratio of 1∶1∶1 of substrate to catalyst and hydrogen peroxide, but unsupported complexes of iron(III) ions showed 55.5% conversion for phenol and 66.4% conversion for cyclohexene at 1∶1∶1 molar ratio of substrate to catalyst and hydrogen peroxide. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 90.5% and 96.5% with supported HPHZ Schiff base complexes of iron(III) ions, but was found to be low with cobalt(II) and nickel(II) ions complexes of Schiff base. The selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was different with studied metal ions and varied with molar ratio of metal ions in the reaction mixture. The selectivity was constant on varying the molar ratio of hydrogen peroxide and substrate. The energy of activation for epoxidation of cyclohexene and phenol conversion in presence of polymer supported HPHZ Schiff base complexes of iron(III) ions was 8.9 kJ mol^?1 and 22.8 kJ mol^?1, respectively, but was high with Schiff base complexes of cobalt(II) and nickel(II) ions and with unsupported Schiff base complexes.