Zeolite-encapsulated 2-(o-aminophenyl)benzimidazole complexes: synthesis,characterization and catalytic activity

Cobalt(II), copper(II) and zinc(II) complexes of 2-(o-aminophenyl)benzimidazole (AmPhBzlH) encapsulated in the super cages of zeolite-Y and ZSM-5 have been synthesized and characterized by spectroscopic studies (IR, UV/visible, EPR), elemental analyses, thermal studies and X-ray diffraction patterns. The catalytic activity of encapsulated complexes was investigated for the hydroxylation of phenol using 30% H₂O₂ as an oxidant. Under optimized reaction conditions, the hydroxylation of phenol yielded catechol and hydroquinone as the major products. All catalysts show good selectivity for diphenol products. A maximum conversion of phenol was obtained with [Cu(AmPhBzlH)]-Y as the catalyst. The results showed that conversion of phenol varies in the order [Cu(AmPhBzlH)]-Y > [Cu(AmPhBzlH)]-ZSM-5 > [Zn(AmPhBzlH)]-Y > [Co(AmPhBzlH)]-Y > [Zn(AmPhBzlH)]-ZSM-5 > [Co(AmPhBzlH)]-ZSM-5 after 6 h of reaction time. Test for the recyclability of the reaction was also carried out and the results indicate their recyclability.     

Catalytic activity of supported solid catalysts for phenol hydroxylation

Cobalt(II), copper(II) and zinc(II) complexes of 2-phenylbenzimidazole (PhBzlH) encapsulated in the supercages of zeolite-Y and ZSM-5 have been synthesized and characterized by spectroscopic studies (IR, UV/visible, EPR), elemental analyses, thermal studies and X-ray diffraction patterns. The catalytic activity of encapsulated complexes was investigated for the hydroxylation of phenol using 30 % H₂O₂ as an oxidant. Under optimized reaction conditions, the hydroxylation of phenol yielded catechol and hydroquinone as the major products. All catalysts show good selectivity for diphenol products. A maximum conversion of phenol was obtained with [Cu(PhBzlH)]-Y as the catalyst. The results showed that conversion of phenol varies in the order [Cu(PhBzlH)]-Y (53 %) > [Cu(PhBzlH)]-ZSM-5 > (49 %) > [Co(PhBzlH)]-ZSM-5 (47 %) > [Co(PhBzlH)]-Y (46 %) > [Zn(PhBzlH)]-Y (45 %) > [Zn(PhBzlH)]-ZSM-5 (41 %) after 6 h of reaction time. Test for the recyclability of the reaction was also carried out and the results indicate their recyclability.     

Metal complexes of 2-methylimidazole encapsulated in zeolite-Y as efficient and reusable catalysts for oxidation of phenol and benzyl alcohol

Copper(II), ruthenium(III) and zinc(II) complexes of 2-methylimidazole (2-MeImzlH) encapsulated in the supercages of zeolite-Y have been synthesized and characterized by various physicochemical measurements. The catalytic potential of these complexes were tested for the oxidation of phenol and benzyl alcohol using 30 % H₂O₂ as an oxidant. Various parameters, such as concentration of oxidant and catalyst, reaction time, temperature of the reaction, volume of solvent and type of solvents have been optimized to obtain the maximum transformation of phenol to catechol and hydroquinone. The catalytic activity of zeolite encapsulated complexes followed the order: [Cu(2-MeImzlH)]-Y (72.5 %) > [Ru(2-MeImzlH)]-Y (57.8 %) > [Zn(2-MeImzlH)]-Y (43.2 %) after 5 h of reaction time. Oxidation of benzyl alcohol catalyzed by these encapsulated complexes gave only benzaldehyde as the product. The zeolite-encapsulated complexes could be easily separated after the reaction and reused. The neat complexes gave low conversions as compared to the encapsulated catalysts and decomposed. The catalytic activity of zeolite encapsulated complexes was found to be better than their respective non-encapsulated complexes and metal exchanged zeolites.     

Liquid-Phase Catalytic Hydroxylation of Phenol Using Cu(II), Ni(II) and Zn(II) Complexes of Amidate Ligand Encapsulated in Zeolite-Y as Catalysts

Copper(II), nickel(II) and zinc(II) complexes of amidate ligand 1,2-bis(2-hydroxybenzamido)ethane(H₂hybe) encapsulated in the super cages of zeolite-Y have been prepared and characterized by spectroscopic studies and thermal as well as X-ray diffraction (XRD) patterns. These complexes catalyze the liquid-phase hydroxylation of phenol with H₂O₂ to catechol as a major product and hydroquinone as a minor product. Considering the concentration of substrate and oxidant, amount of catalyst, temperature of the reaction and volume of solvent, a best-suited reaction condition has been optimized to get maximum hydroxylation. Under the optimized reaction conditions, [Cu(hybe)]-Y has shown the highest conversion of 40% after 6h, which is followed by [Ni(hybe)]-Y with 37% conversion and [Zn(hybe)]-Y has shown the poorest performance with 33% conversion. All these catalysts are more selective towards catechol formation (90%), irrespective of their catalytic performance.     

Dioxovanadium(V) Complexes of Dibasic Tridentate Ligands Encapsulated in Zeolite-Y for the Liquid Phase Catalytic Hydroxylation of Phenol Using H2O2 as Oxidant

Liquid phase hydroxylation of phenol with H₂O₂to a mixture of catechol and hydroquinone in acetonitrile has been reported using dioxovanadium(V) Schiff base complexes encapsulated in zeolite-Y as catalysts. The Schiff bases used are derived from salicylaldehyde and isonicotinic acid hydrazide (H₂sal-inh) or o-aminophenol (H₂sal-oap). A best-suited reaction condition has been optimized for both the catalysts by considering concentration of the oxidant, amount of catalyst and temperature. Under the optimized reaction conditions, catalytic ability of both the catalysts is comparable and has shown the highest conversion of about 27% after 6 h of reaction time. Both the catalysts are more selective towards catechol formation where NH₄[VO₂(sal-inh)] gives 84.6% selectively while NH₄[VO₂(sal-oap)] gives 77% selectivity.     

Host (nanocavity of zeolite-Y)/guest (Mn(II), Co(II), Ni(II) and Cu(II) complexes of pentadendate Schiff-base ligand) nanocomposite materials (HGNM): application in the heterogeneous oxidation of cyclohexene

Transition metal (M = Mn(II), Co(II), Ni(II) and Cu(II)) complexes with pentadendate Schiff-base ligand; N,N′-bis(salicylidene)-2,6-pyridinediaminato, H₂ [sal-2,6-py]; was entrapped in the nanocavity of zeolite-Y by a two-step process in the liquid phase: (i) adsorption of bis(salicylaldiminato)metal(II); [M(sal)₂]-NaY; in the supercages of the zeolite, and (ii) in situ Schiff condensation of the metal(II) precursor complex with the corresponding 2,6-pyridinediamine; [M(sal-2,6-py)]-NaY. The new materials were characterised by several techniques: chemical analysis, spectroscopic methods (DRS, BET, FTIR and UV/Vis), conductometric and magnetic measurements. Analysis of the data indicates that the M(II) complexes are encapsulated in the nanodimensional pores of zeolite-Y and exhibit different from those of the free complexes, which can arise from distortions caused by steric effects due to the presence of sodium cations, or from interactions with the zeolite matrix. The Host–Guest Nanocomposite Materials (HGNM); [M(sal-2,6-py)]-NaY; catalyzes the oxidation of cyclohexene with tert-butylhydroperoxide (TBHP). Oxidation of cyclohexene with HGNM gave 2-cyclohexene-1-one, 2-cyclohexene-1-ol and 1-(tert-butylperoxy)-2-cyclohexene. [Mn(sal-2,6-py)]-NaY shows significantly higher catalytic activity than other catalysts.     

Syntheses,crystal structures and luminescent investigations of cobalt(II) and zinc(II) complexes with 2-propyl-4,5-dicarboxylate-imidazole (H3PIDC)

Presented in this communication are four metal complexes based on 2-propyl-4,5-dicarboxylate-imidazole (H₃PIDC), including two Co(II) coordination compounds, [Co(H₂PIDC)₂(H₂O)₂] · 4H₂O (1) and 2[Co(H₂PIDC)₂(H₂O)₂] · 5H₂O (2), as well as two Zn(II) coordination compounds, [Zn(H₂PIDC)₂(H₂O)₂] · 4H₂O (3) and 2[Zn(H₂PIDC)₂(H₂O)₂] · 7H₂O (4). They contain the same coordinated unit of [M(H₂PIDC)₂(H₂O)₂] (M = Zn or Co). Interestingly, among these four complexes, 1 and 2, or 3 and 4 crystallized in different space group, which may be related with the number of the crystallized H₂O molecules.     

Synthesis and Catalytic Activity of Cu(II), Fe(III) and Bi(III) Complexes of Thio-Schiff Base Encapsulated in Zeolite-Y for Hydroxylation of Phenol

Coordination of 4-{[(1E)-(2-hydroxyphenyl)methylene]amino}-2,4-dihydro-3H-1,2,4-triazole-3-thione, [sal(thiotriazol)], with M-exchanged zeolite-Y (M = Cu(II), Fe(III) and Bi(III)) leads to the encapsulation of the metal complexes in the supercages of zeolite-Y by flexible ligand method. The prepared encapsulated metal complexes have been characterized by physico-chemical techniques, which indicated that the complexes were effectively encapsulated inside the supercages of Na–Y, without any modification of the morphology and structure of the zeolite. 3D model structure generated for these complexes suggests that zeolite-Y can accommodate these complexes in the FAU supercages without any strain. The catalytic activity of all the catalysts towards the hydroxylation of phenol was evaluated under heterogeneous conditions using hydrogen peroxide as an oxidant. Under the optimized conditions, these catalysts show moderate activity with excellent selectivity (>95%) towards catechol. These catalysts were stable in hydroxylation of phenol and have been reused a further three times after recovering. The results reflect the reusability of the catalysts, as no significant loss in their catalytic activity was noticed.     

Cobalt(II), Zinc(II) and Cadmium(II)-Squarate Complexes with N-Methylimidazole

Three M(II)-squarate complexes, [Co(sq)(H₂O)(Nmim)₄] (1), [Zn(μ_1,3-sq)(H₂O)₂ (Nmim)₂] _n (2) and [Cd(μ_1,3-sq)(H₂O)₂(Nmim)₂] _n (3) (sq = squarate, Nmim = N-methylimidazole) have been synthesized and characterized by elemental, spectral (IR and UV–Vis.) and thermal analyses. The molecular structures of the complexes have been investigated by single crystal X-ray diffraction technique. The squarate ligand acts as two different coordination modes as a monodentate (in 1) and bis(monodentate) (O ^1– O ³ ) bridging ligand (in 2, 3). The Co(II) atom has a distorted octahedral geometry with the basal plane comprised of three nitrogen atoms of Nmim ligands and a oxygen atom of squarate ligand. The axial position is occupied by a nitrogen atom of Nmim and one aqua ligand. The crystallographic analysis reveals that the crystal structures of 2 and 3 are one-dimensional linear chain polymers along the c and b axis, respectively. The configuration around each metal(II) ions are distorted octahedral geometry with two nitrogen atoms of trans-Nmim, two aqua ligands and two oxygen atoms of squarate-O¹,O³ ligand. These chains are held together by the C–H···π, π···π and hydrogen-bonding interactions, forming three-dimensional network.     

Copper(II) and cadmium(II) complexes derived from Strandberg-type polyoxometalate clusters: Synthesis,crystal structures,spectroscopy and biological activities

Three Strandberg-type polyoxometalate compounds [Cu(L)₂(H₂O)₂]₂H₂[P₂Mo₅O₂₃]·2CH₃OH (1), [Cu(L)₂(H₂O)]H₂[Cu(L)₂(P₂Mo₅O₂₃)]·4H₂O (2), [Cd(L)₂(H₂O)₂]₂H₂[P₂Mo₅O₂₃]·2CH₃OH (3), (L = pyridine-2-carboxamide) have been synthesized and structurally characterized by elemental analysis, spectroscopic methods (IR and UV–vis) as well as single crystal X-ray diffraction. Single-crystal X-ray structural analyses indicate that 1 and 3 are isostructural and crystallized in monoclinic, space group I2/a. Biological studies have indicated that compounds 1–3 exhibit broad and effective activities against the tested cells. A synergistic effect involving L, metal and P₂Mo₅ could probably explain the improved growth-inhibiting properties. Both coordination mode and the type of metal ion play significant roles in these compounds cytotoxicity.     

EXTRACTION CHEMISTRY OF COBALT AND NICKEL BY DI(1-METHYLHEPTYL)PHOSPHINIC ACID

The fundamental characteristics and mechanism of extraction of cobalt (II) and nickel(II) by di-(1-methylheptyl) phosphinic acid (DMHPA) were studied. The extraction ability of cobalt(II), nickel (II) and various metals by DMHPA decreases in the order Fe(III) > Zn ? Pb(II) > Mn(II) > Cu(II) > Co(II) > Mg > Ca > Ni(II). The difference of the pH_½ values for nickel and cobalt reaches 2.06 pH units, which is apparently greater than those from extraction by di(2-ethylhexyl)phosphoric acid (DEHPA)and 2-ethyl-hexyl ester 2-ethylhexylphosphonic acid(DHEHPA).The slope analysis and IR spectroscopy reveal that the stoichiometrics of cobalt and nickel extracted species are Co(HA₂)₂ and Ni(HA₂)₂(H₂O)₂ respectively. As demonstrated by the study of the electronic spectroscopy the structure of the extracted complexes were shown as tetrahedral and octahedral configuration respectively. Furthermore, the coordination field parameters of the complexes were calculated.     

Host (nanopores of zeolite Y)-guest (oxovanadium(IV) tetradentate schiff-base complexes) nanocomposite materials: synthesis,characterization and liquid phase hydroxylation of phenol with hydrogen peroxide

Oxovanadium(IV) tetradentate Schiff-base complexes; [VO(X₂-haacac)] (X = H, Cl, CH₃ and NO₂), X₂-haacac = substituted bis(2-hydroxyanil)acetylacetone; and encapsulated in the nanopores of zeolite NaY; [VO(X₂-haacac)]-NaY; have been synthesized and characterized. The host-guest nanocomposite materials; [VO(X₂-haacac)]-NaY; was characterized by chemical analysis and spectroscopic methods (FT-IR, UV/VIS, XRD, BET and DRS). The analytical data indicated a composition corresponding to the mononuclear complex of Schiff-base ligand. The characterization data showed the absence of extraneous complexes, retention of zeolite crystalline structure and encapsulation in the nanopores. Substitution of the aromatic hydrogen atoms of the Schiff-base ligand by electron withdrawing groups like −Cl, and −NO₂ has two major effects: (1) retention and concentration of the oxovanadium(IV) complex in the zeolite cavities is enhanced (due to the larger size of the substituents) and (2) the electronic and spectral properties of the encapsulated complex are modified. Liquid-phase selective hydroxylation of phenol with H₂O₂ to a mixture of catechol and hydroquinone in CH₃CN has been reported using oxovanadium(IV) Schiff-base complexes encapsulated in zeolite-Y as catalysts. Reaction conditions have been optimized by considering the concentration of substrate and oxidant, amount of catalyst, effect of time, volume of solvent and temperature. Under the optimized reaction conditions, [VO((NO₂)₂-haacac)]-NaY has shown the highest conversion of 42.3% after 6 h. All these catalysts are more selective toward catechol formation. Encapsulated oxovanadium(IV) complex is catalytically very efficient as compared to other neat complexes for the hydroxylation of phenol and is stable to be recycled without much deterioration.     

Two helical one-dimensional copper(II) coordination polymers based on N-(2-hydroxylbenzyl)glycine and N-(2-hydroxylbenzyl)-l-alanine: Syntheses,crystal structures and magnetic studies

Two new helical Cu(II) coordination polymers, [Cu(2,2′-bpy)(Hsgly)]Cl · 2H₂O(H₂sgly = N-(2-hydroxylbenzyl)glycine) (1) and [Cu(2,2′-bpy)(Hsala)](NO₃) · 2H₂O(H₂sala = N-(2-hydroxylbenzyl)-l-alanine) (2) were synthesized. Single crystal X-ray diffraction analysis indicated that both complexes showed helical chains arrangement of Cu(II) centers bridged by carboxyl groups. The magnetic measurements showed complex 1 exhibited ferromagnetic interaction while there was no interaction between the Cu(II) centers in complex 2.     

The Synthesis and Characterization of Star Shaped Metal Complexes of Triazine Cored Schiff Bases: Their Thermal Decompositions and Magnetic Moment Values

Tripodal ligand III, 2,4,6-tris(4-hydroxybenzimino)-1,3,5-triazine, was synthesized by reacting melamine with 4-hydroxybenzaldehyde. (E)-4-Bromo-2-((2-bromoethylimino)-methyl)phenol VI was obtained by reaction of 5-bromo-2-hydroxybenzaldehyde and 2-bromoethanamine hydrochloride. Melamine cored tripodal Schiff base VII (H₃L) was synthesized by reacting III with VI. Tripodal metal complexes were obtained by reacting H₃L and transition metal salts. The complexes were characterized by elemental analyses, FT-IR, ¹H NMR and LC–MS spectroscopy, thermal analyses and magnetic measurements. Finally, metal ratios of the complexes were determined by atomic absorption spectroscopy. The complexes are square-planar low-spin (S = 1/2) Co(II), diamagnetic square-planar Ni(II), square-planar (S = 1/2) Cu(II) and diamagnetic tetrahedral Zn(II).     

A weak-link approach to the synthesis of copper(II)-based metallacycles using a flexible hemilabile 4,7-diazadecanediamide ligand

Employment of a weak-link approach to the synthesis of Cu(II) metallacycle [Cu₂(C₈H₁₈N₄O₂)₂(C₂H₈N₂)₂] · 4Cl (2) from [Cu(C₈H₁₈N₄O₂)(Cl)]Cl · 2H₂O (1) under very mild reaction conditions was achieved in high yield using a flexible hemilabile multidentate ligand, 4,7-diazadecanediamide.     

Adsorption of Cr(III), Ni(II), Zn(II), Co(II) ions onto phenolated wood resin

In this study, phenolated wood resin was used an adsorbent for the removal of Cr(III), Ni(II), Zn(II), Co(II) ions by adsorption from aqueous solution. The adsorption of metal ions from solution was carried at different contact times, concentrations and pHs at room temperature (25°C). For individual metal ion, the amount of metal ions adsorbed per unit weight of phenolated wood resin at equilibrium time increased with increasing concentration and pH. Also, when the amounts of metal ions adsorbed are compared to each other, it was seen that this increase was order of Cr(III) > Ni(II) > Zn(II) > Co(II). This increase was order of Cr(III) > Ni(II) > Co(II) > Zn(II) for commercial phenol–formaldehyde resin. Kinetic studies showed that the adsorption process obeyed the intraparticle diffusion model. It was also determined that adsorption isotherm followed Langmuir and Freundlich models. Adsorption isotherm obtained for commercial phenol–formaldehyde resin was consistent with Freundlich model well. Adsorption capacities from Langmuir isotherm for commercial phenol–formaldehyde resin were higher than those of phenolated wood resin, in the case of individual metal ions. Original adsorption isotherm demonstrated the monolayer coverage of the surface of phenolated wood resin. Adsorption kinetic followed the intraparticle diffusion model. The positive values of ΔG° determined using the equilibrium constants showed that the adsorption was not of spontaneous nature. It was seen that values of distribution coefficient (K_D) decreasing with metal ion concentration in solution at equilibrium (C_e) indicated that the occupation of active surface sites of adsorbent increased with metal ions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2838–2846, 2006     

Cationic Mobility Via Cation-Exchange Mechanism on Poly(8-Hydroxyquinoline) Matrix

The insertion of Al(III) cation into a poly(8-Hydroxyquinoline) (PHQ) instead of some metal ions such as Co(II), Ni(II), Zn(II) or Fe(III) ions via cation-exchange mechanism has been studied by several techniques. The presence of Al(III) and the absence of Co(II) cations has been proved by elemental analysis of the polymer chelates product. Molecular mechanics (MM+) calculations showed that the potential energy (PE, kJ mol⁻¹) of the optimum molecular geometric structure (OMG) of the PHQ–Al(III) matrix is about seventy-six (76.185) greater than the PE of the PHQ–Co(II) complex. The TGA thermograms show that the PHQ–Al(III) matrix is thermally unstable than the PHQ–Co(II) complex under the same conditions. These observations indicate that the PHQ–Al(III) is expanded coil-like form. So, the thermal decomposition of PHQ–Al(III) complex is easy than the compacted coil-likes form of PHQ–Co(II) complex. The incorporation of Al(III) ion via cation-exchange properties have been investigated by spectrophotometric technique. The decrease of the absorbance at about ~370 nm of PHQ–Co(II) complex associated with increasing concentration of Al(III) revealed the replacement of that metal ion by Al(III) into PHQ chain. The cation-exchange constant (K _ex) of the divalent ions [Ni(II), Co(II), Cr(II), Zn(II), Mn(II), Mg(II) and Cu(II)] from PHQ–M(II) by the additions of Al(III) according to the following series: Ni(II) > Co(II) > Cr(II) > Cu(II) > Zn(II) > Mn(II) > Mg(II).     

A new copper(II) di-μ2-carboxylato bridged dinuclear complex: [Cu(oda)phen]2 · 6H2O (oda = oxydiacetate,phen = phenanthroline)

The oxydiacetate-bridged copper(II) complex [Cu(oda)(1,10-phen)] · 3H₂O (oda = oxydiacetate dianion, 1,10-phen = 1,10-phenanthroline) has been characterized. The complex is dinuclear and centrosymmetric with each copper atom residing in a CuN₂O₄ octahedral environment. The Cu(II) ions are bridged by two carboxylate-oxygen atoms in a strictly planar Cu₂O₂ core with a Cu–Cu distance of 3.417(2) Å. The magnetic susceptibility measurements (2–300 K) show weak ferromagnetic coupling between the copper ions with J = 3.3 cm⁻¹. The results are compared with those of the homologous [Cu(tda)(1,10-phen)]₂tda (tda = thiodiacetate dianion). A model proposed for the electronic structures of the complexes based on the density functional theory (DFT) satisfactorily accounts for the magnetic results.     

Single-step catalytic synthesis of diphenyl carbonate over transition-metal-substituted Keggin-type tungstophosphoric acid

Single-step catalytic synthesis of diphenyl carbonate (DPC) through the transesterification of dimethyl carbonate (DMC) and phenol could be firstly arrived by using the transition-metal-substituted polyoxometalates (TMS-POMs) K₅[PW₁₁O₃₉M(H₂O)]/TiO₂ system (M = Mn^II, Co^II, Ni^II, Cu^II, Zn^II). The catalytic activity of this transesterification was strongly influenced by the type of transition metal in the TMS-POMs. Among them, the K₅[PW₁₁O₃₉Zn(H₂O)]/TiO₂ catalytic system showed the highest activity and selectivity for DPC. The conversion of phenol reached 12.8%, and the selectivity to DPC was 83.6%. The turnover number (TON) reached 6.44 × 10⁴ mol/mol [PW₁₁O₃₉Zn(H₂O)]⁵⁻/TiO₂. A possible mechanism that the transition metal in the polyoxometalates anchored DMC to form intermediate compound in the transesterification was proposed.     

Nanodimensional microreactors encapsulation of 15- and 16-membered diaza dioxa macrocyclic Schiff-base copper(II) complex nanoparticles: Synthesis and characterization

Copper(II) complexes with 15- and 16-membered diaza dioxa Schiff-base macrocyclic ligands “[Cu(R[15 or 16]N₂O₂)]²⁺ (R = Et, Pr, Ph, Ch)” were entrapped in the nanopores of zeolite-Y by a three-step process in the liquid phase: (i) exchange of Cu(II) ions with NaY in water solution, (ii) reaction of Cu(II)–NaY with excess 1,3-bis(2-carboxyaldehydephenoxy)propane (O₂O₂) in methanol, [(1,3-bis(2-carboxyaldehydephenoxy)propane)copper]²⁺@NaY, [Cu(O₂O₂)]²⁺@NaY (iii) template synthesis of [Cu(O₂O₂)]²⁺@NaY with diamine. The obtained new complex nanoparticles entrapped in the nanopores of zeolite Y have been characterized by elemental analysis FT-IR, XPS, DRS, UV–vis spectroscopic techniques, molar conductance, magnetic moment data, XRD and nitrogen adsorption. Analysis of data indicates all of the complexes have been encapsulated within nanopores without affecting the zeolite framework structure.