Oxovanadium(IV) Schiff Base Complexes Encapsulated in Zeolite-Y as Catalysts for the Liquid-Phase Hydroxylation of Phenol

Liquid-phase hydroxylation of phenol with H₂O₂ to a mixture of catechol and hydroquinone in acetonitrile 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, volume of solvent and temperature. Under the optimized reaction conditions, [VO(sal-1,3-pn)]-Y (H₂sal-1,3-pn = N,N'-bis(salicylidene)propane-1,3-diamine) has shown the highest conversion of 34.3% after 6 h, [VO(salen)]-Y (H₂salen = N,N'-bis(salicylidene)ethane-1,2-diamine) and [VO(saldien)]-Y (H₂saldien = N,N'-bis(salicylidene)- diethylenetriamine) have comparable catalytic activity (33% conversion) while [VO(sal-1,2-pn)]-Y (H₂sal-1,2-pn = N,N'-bis(salicylidene)propane-1,2-diamine) has the poorest performance (10.6% conversion). All these catalysts are more selective (90%) toward catechol formation except [VO(sal-1,3-pn)]-Y, which only gives 68% selectivity.     

Zeolite encapsulated Ru(III), Cu(II) and Zn(II) complexes of benzimidazole as reusable catalysts for the oxidation of organic substrates

Ru(III), Cu(II) and Zn(II) complexes of benzimidazole (BzlH) have been synthesized in the supercages of zeolite-Y by the flexible ligand method and were characterized by spectroscopic (IR, UV–Vis and ESR) studies, XRD and thermogravimetric analysis, surface area, and pore volume measurements. The zeolite encapsulated complexes catalyzed the oxidation of ethylbenzene, benzoin, and cyclohexanol. Various parameters, such as concentration of oxidant and catalyst, reaction time, temperature of the reaction and type of solvents have been optimized to obtain the maximum transformation of ethylbenzene to a mixture of acetophenone, benzaldehyde and styrene. Under the optimized reaction conditions, [Ru(BzlH)]-Y gave 80.4 % conversion of ethylbenzene in 1 h. All these zeolite encapsulated complexes were more selective towards acetophenone formation. Oxidation of benzoin catalyzed by [Cu(BzlH)]-Y, [Ru(BzlH)]-Y and [Zn(BzlH)]-Y encapsulated complexes resulted in 75.5, 78.7 and 59.9 % conversion respectively to give benzaldehyde as exclusive product. A maximum conversion of 39.1 % cyclohexanol with [Cu(BzlH)]-Y was achieved to give cyclohexanone. The activity of neat complexes towards these reactions was also carried out. The encapsulated catalysts were significantly more active than neat complexes and recyclable without much loss in catalytic activity.     

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.     

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.     

Cobalt(II), Copper(II) and Zinc (II) complexes of 2-methyl benzimidazole encapsulated in zeolite as catalysts for the hydroxylation of phenol

Cobalt(II), Copper(II) and Zinc (II) complexes of 2-methylbenzimidazole (Mebzlh) encapsulated in the super cages of zeolite-Y and ZSM-5 have been synthesized by flexible ligand method and characterized by various physico-chemical measurements. The catalytic activity of encapsulated complexes was investigated for the decomposition of H₂O₂ and for the hydroxylation of phenol using H₂O₂ as an oxidant. The hydroxylation of phenol yielded catechol and hydroquinone as the major products. All catalysts show good selectivity for diphenol products. The results showed that conversion of phenol varies in the order [Cu(Mebzlh)]-Y > [Cu(Mebzlh)]-ZSM-5 > [Zn(Mebzlh)]-Y > [Co(Mebzlh)]-Y > [Zn(Mebzlh)]-ZSM-5 > [Co(Mebzlh)]-ZSM-5 after 6 h of reaction time.     

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.     

Synthesis of New Polyimides from Ru (II) Complex of 2,6-bis [1-(p-dimethylaminophenylimino) Ethyl] Pyridine

Pyridine-based tridentate ligand containing pendant NMe₂ unit was used to prepare novel polyimides via one-stage solution polycondensation due to their stability under a variety of oxidative and reductive conditions. Ru (II) complex of the pydim ligand was synthesized starting from [RuCl₂ (p-cymene)]₂ and 2,6-bis [1-(p-dimethylaminophenylimino) ethyl] pyridine. A series of stable polyimides were synthesized from Ru (II) complex of 2,6-bis [1-(p-dimethylaminophenylimino) ethyl] pyridine (2) and various aromatic dianhyrides had inherent viscosities ranging from 1.31 to 1.55 dL/g and were soluble in polar solvents. The glass transition temperatures were 245–308°C, and the 10% weight loss temperatures were above 482–548°C.     

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.     

Air Stable Iron(II) PNP Pincer Complexes as Efficient Catalysts for the Selective Alkylation of Amines with Alcohols

A series of well‐defined iron(II) complexes of the types [Fe(PNP)Br₂] and [Fe(PNP)(CO)Br₂] with PNP pincer ligands based on triazine and pyridine backbones were prepared and fully characterized. These complexes were tested as catalysts for the alkylation of amines by alcohols. The high‐spin complexes [Fe(PNP)Br₂] are catalytically inactive. The low‐spin complexes [Fe(PNP)(CO)Br₂] bearing a carbonyl co‐ligand efficiently and selectively convert primary alcohols and aromatic and benzylic amines selectively into mono‐N‐alkylated amines in good to excellent isolated yields. A mechanistic proposal is given.

     

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.     

Neutral Pd(II) and Ni(II) Acetylide Catalysts for the Polymerization of Methyl Methacrylate

Homogenous polymerization of methyl methacrylate using Pd(II)- and Ni(II)-based acetylide complexes as initiators has been investigated. M(PR'₃)₂(CCR)₂ (M=Pd, Ni; R'=PPh₃, Pn-Bu₃; R=Ph, CH₂OH, CH₂OOCCH₃, CH₂OOCPh, CH₂OOCPhOH-o) were found to be a novel type of effective initiators for the polymerization of methyl methacrylate. Among them, Pd(C CPh)₂(PPh₃)₂ (PPP) shows the highest activity in the MMA polymerization and the PMMA obtained is a syndiotactic polymer with high number-average molecular weight (M _n) of 14.1 × 10⁴. Some features and kinetic behavior of MMA polymerization initiated by PPP were studied in detail. The polymerization reaction is first-order with respect to both [PPP] and [MMA]. Radical polymerization mechanism is proposed.     

Formation, Characterization and Electrical Conductivity of Polycarbosilazane-Cu(II), -Ni(II) and -Cr(III) Chloride Metallopolymers

A series of transition metal-polycarbosilazane complexes have been prepared by the reaction of poly(N,N-bis(dimethylsilyl)ethylenediamine), [–Si(CH₃)₂NHCH₂CH₂NH–] _n , with Cu(II), Ni(II), and Cr(III) chloride. The resulting complexes were characterized by infrared (FT-IR) and UV-visible spectroscopy, magnetic susceptibility measurements, thermogravimetric analysis (TGA), and powder X-ray diffraction (XRD). The average chain-chain spacing in these materials were estimated from XRD data and found to be 6.88, 7.91, 7.09, and 6.33 Å in metal-free, Cu(II)-, Ni(II)-, and Cr(III)-containing polycarbosilazanes, respectively. DC electrical conductivity measurements showed that all these metal-polycarbosilazane complexes exhibit semiconductor behavior while the metal-free matrix is an insulator.     

Crown ether bridged homo- and heterodinuclear copper(II) and nickel(II) cyclidene complexes: Interaction with anions

Homodinuclear (3CuCu, 3NiNi) and heterdionuclear (3CuNi) cyclidene complexes linked by two 1,10-diaza-18-crown-6 ethers were synthesized and their properties characterized. For the 3CuCu in the negative potential range the mixed-valence state Cu^I-Cu^II was observed and the comproportionation constants were determined. The redox potentials of M^II/III showed a good correlation with DN of the solvent. In acetonitrile solution containing 0.1 mol dm⁻³ Bu₄NPF₆ reversible M^II/III redox processes were observed. However, in the presence of stronger ion pairing anions (e.g. BF₄⁻ and ClO₄⁻) the “potential inversion” occurred. Redox potentials of dinuclear complexes were compared with mononuclear cyclidene complexes. The influence of selected anions (Cl⁻ and NO₃⁻) on the redox process M^II/III was studied. The effect of Cl⁻ anion was different for 3CuCu and 3NiNi. In 3CuCu coordination of two chloride anions took place after oxidation of copper centers. In the 3NiNi complex two Cl⁻ anions were coordinated to one of the nickel(II) centers facilitating oxidation, at different potentials, of both nickel(II) cations. The behaviour of heteronuclear complex with Cl⁻ anions was similar to 3NiNi. All dinuclear complexes interacted with NO₃⁻ anions and the observed potential shifts were larger for nickel(II) than for copper(II) cations.     

Synthesis of Fe-MCM-48 and its catalytic performance in phenol hydroxylation

Highly ordered Fe-MCM-48 was synthesized by a mixed templation method under low molar ratio (0.17:1) of mixed surfactants to silica and characterized by XRD, ²⁹Si-MAS NMR, ESR, and UV-Visible. Its catalytic activity and selectivity was studied for phenol hydroxylation using H₂O₂ (30%). The substituting element (Fe³⁺) is partially incorporated into the framework position forming a new type of active site which raises the phenol conversion to 43.6% and the diphenol (the mixture of catechol (CAT) and hydroquinone (HQ)) selectivity to 97.7%.     

Synthesis and characterization of soluble (porphyrinato)iron(II) polymers

The use of (tetrakis(4-hexylphenyl)porphyrinato)Fe(II) in polymerization reactions with bidentate ligands such as 9,10-diisocyanoanthracene and 1,4-diisocyanobenzene led to well-defined stacked polymers1 and2 which are still soluble in common organic solvents such as chloroform, dichloromethane, and tetrahydrofurane. They have been completely characterized by¹H-NMR and UV/vis spectropscopy in solution, even allowing end-group analysis for determination of the average degree of polymerization, yieldingn=10 andn=5 for1 and2, respectively. Mößbauer and IR spectroscopy further established the strong Fe-CN bonding reflected by very small isomer shifts and quadrupole splittings (E _Q0.2 mm s^–1) and a large decrease in the IR stretching frequency (v _CN60 cm^–1). The axially stacked polymers exhibit semiconducting properties only upon doping.Presented at the 5th International Symposium on Macromolecule-Metal Complexes (MMV), Summer 1993 in Bremen, Germany.     

The structures and decomposition products of palladium(II) and platinum(II) terpyridine phenoxide complexes

A series of complexes of formula [Pd(OR)(terpy)]BF₄ and [Pt(OR)(terpy)]BF₄ (ROH=a substituted phenol; terpy=2,2^′:6^′,2^″-terpyridine) have been prepared by reaction of [M(OH)(terpy)]BF₄ (M=Pd, Pt) with ROH. One Pd(II) and one Pt(II) complex in this series have been structurally characterised. These compounds are very acid sensitive; decomposition products resulting from recrystallisation of two of these compounds from MeNO₂ or MeCN have been crystallographically characterised.     

Synthesis, Characterization and Anti-microbial Activity of Oligo-N-2-aminopyridinylsalicylaldimine and Some Oligomer-metal Complexes

The oxidative polycondensation and optimum reaction conditions of N-2-aminopyridinylsalicylaldimine using air oxygen, H₂O₂ and NaOCl were determined in an aqueous alkaline solution between 40–90°C. Oligo-N-2-aminopyridinylsalicylaldimine (OAPSA) was characterized by using ¹H-NMR, FT-IR, UV-vis and elemental analysis. N-2-aminopyridinylsalicylaldimine was converted to oligomer by oxidizing in an aqueous alkaline medium. The number average molecular weight (M _n), weight average molecular weight (M _w) and polydispersity index (PDI) values were found to be 7487 gmol^–1, 7901 gmol^–1 and 1.06, respectively. According to these values, 70% of N-2-aminopyridinylsalicylaldimine turned into oligo-N-2-aminopyridinylsalicylaldimine. During the polycondensation reaction, a part of the azomethine (–CH=N–) groups oxidized to carboxylic (–COOH) group. Besides, the structure and properties of oligomer-metal complexes of oligo-N-2-aminopyridinyl salicylaldimine (OAPSA) with Cu (II), Ni (II), and Co (II) were studied by FT-IR, UV-vis DTA, TG and elemental analysis. Anti-microbial activities of the oligomer and its oligomer-metal complexes have been tested against C. albicans, L. monocytogenes, B. megaterium, E. coli, M. smegmatis, E. aeroginesa, P. fluorescen and B. jeoreseens. Also, according to the TG and DTA analyses, oligo-N-2-aminopyridinylsalicylaldimine and its oligomer-metal complexes were found to be stable thermo-oxidative decomposition. The weight loss of OAPSA found to be 20%, 50% and 98% at 350°C, 535°C and 1000°C, respectively.     

Synthesis of Lead(II) Minoxidil Coordination Polymer: A New Precursor for Lead(II) Oxide and Lead(II) Hydroxyl Bromide

A new lead(II) coordination polymer, [PbBr₂(C₉H₁₅N₅O)]_n (1), where C₉H₁₅N₅O is (2,4-diamino-6-piperidine-1-yl) pyrimidine N-oxide (minoxidil) is synthesized and characterized. Polymer 1 is synthesized in methanol by sonochemical and hydrothermal methods from lead(II) acetate, KBr and the minoxidil ligand. The crystal structure of [PbBr₂(C₉H₁₅N₅O)]_n indicates a syndiotactic coordination polymer. The Pb(II) atom lies on a mirror plane; the mirror plane is perpendicular to the pyrimidine ring bisecting the piperidine ring. N–H···O intramolecular and C–H···Br, N–H···N strong intermolecular interactions were observed. Micro-rods of PbO and nano-plates of PbOHBr were prepared by thermal decomposition of the nano-structured [PbBr₂(C₉H₁₅N₅O)]_n as a precursor. Characterization of the products was carried out using X-ray crystallography, elemental analysis, FTIR spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis and thermal analysis. The sonochemical method resulted in a significant reduction of reaction time, reaction temperature and particle sizes of the products.     

Syntheses and Structural Analytical Studies of Two Co(II) Complexes Based on 1,4-Di(benzimidazole-1-yl)benzene

Two new Co(II) complexes of 1,4-di(benzimidazole-1-yl)benzene ligand (L) with the formulas [(CoLCl₂)(CHCl₃)(DMF)]_∞ (1) and [CoL(NO₃)₂]_∞ (2) have been synthesized by anion-directed self-assembly. Both complexes have been characterized by elemental analyses, IR, and X-ray single crystal diffraction. Complexes 1 and 2 exhibit 1D chain structures. In 1, Co(II) ions possess a distorted tetrahedral coordination environment composed of N₂Cl₂ donors from two L ligands and two chloride ions, while the Co(II) ions in 2 reveal a distorted octahedral structure defined by the N₂O₄ donors from two L ligands and two nitrate anions. These results illustrate that the anions play an important role in the self-assembly of metal–organic materials.     

Formation of Chini type Pt-Co complexes in basic zeolites

Colored samples are obtained upon CO reaction at room temperature with Pt²⁺ ions incorporated in basic zeolites such as PtNaY and PtCsNaX. Their characterization, carried out by UV-visible and infrared spectroscopy, show strong analogies with Chini complexes. This suggests that complexes [Pt₃(CO₃(₂CO)₃]^2– _n of the Chini type may be formed and stabilized in the supercages of basic zeolites.