Polymer-supported diimine molybdenum carbonyl complexes as highly reusable and efficient pre-catalysts in epoxidation of alkenes

By reaction of aldehydic polystyrene and ethylene diamine, polystyrene–imine–amine reagent was produced. Reaction of this reagent with benzaldehyde and 4-nitrobenzaldehyde resulted in polystyrene-diimines (3a and 3b). These reagents were used for the immobilization of molybdenum hexacarbonyl. The functionalized polystyrene and supported-diimine molybdenum carbonyl catalysts were characterized by FT-IR spectrum and CHN analysis. The molybdenum content of catalysts was determined by neutron activation analysis. Supported-diimine molybdenum carbonyl pre-catalysts (3aM and 3bM) were used in epoxidation of cyclooctene, and the reaction parameters such as solvent and oxidant were optimized and the epoxidation of different alkenes was investigated in optimizing these conditions. The obtained results in the presence of polymer-supported diimine molybdenum carbonyl pre-catalysts (3aM and 3bM) showed that they were very active and selective in the epoxidation of a wide range of alkenes. The reusability of the supported pre-catalysts was also studied. The results showed that they were highly reusable in epoxidation of alkenes.     

Zur Kenntnis der Substitutionsprodukte der (2H)-Imidazol-4(3H)-thione und 2H-Imidazol-4(3H)-one

2H-Imidazole-4(3H)-thiones (a), available from methyl alkyl and methyl aryl ketones with sulfur and ammonia, react via their corresponding N-sodium compounds or in presence of tert. amines with alkyl and aryl carboxylic acid chlorides to give the corresponding intensely coloured (orange to violett) cryst. 3-acyl-2H-imidazole-4(3H)-thiones4 a-q and6–26. With dicarboxylic acid dichlorides the colourless cryst. N,N′-diacyl-bis-3-imidazoline-5-thiones5 a-d and27–32 are obtained. With carbamic acid chlorides and chloroformic acid esters the corresponding urea (33–35) and urethane derivatives36, 37 are formed. In an analogous way 2H-imidazol-4(3H)-ones react with acid chlorides to 3-acyl-2-imidazol-4(3H)-ones (44–50), which can also be obtained by treating the corresponding 3-acyl-2H-imidazole-4(3H)-thione with KMnO₄.     

Neutral and monocationic dinuclear (carbonyl)(cyclopentadienyl)(phenylchalcogenate) iron complexes of the general formulas [(RC5H4)Fe(CO)EPh]2 and [(RC5H4)Fe(CO)EPh]2PF6 (E = S or Te; R = H or Me): Synthesis, molecular structures, and EPR spectra

Heating of the compounds (RC₅H₄)Fe(CO)₂TePh (R = H (I) and Me (II)) in heptane afforded the dinuclear complexes [(RC₅H₄)Fe(CO)TePh]₂ (III and IV, respectively). By oxidation with Fc⁺PF ₆ ^? , these complexes were transformed into the paramagnetic cationic complexes [(RC₅H₄)Fe(CO)TePh]₂PF₆ (V and VI, respectively). Structures III–V and [(C₅H₅)Fe(CO)SPh]₂PF₆ (VII) were characterized by X-ray diffraction.     

Heterobimetallic dioxomolybdenum(VI) complexes derived from bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone: Synthesis and characterization

The heterobimetallic complexes [MMoO₂(L)(H₂O)₂] (where M = Zn²⁺ (1), Cu²⁺ (2), and Co²⁺ (4)) and [{MMoO₃(H₂L)(H₂O)₂}₂] (where M = Ni²⁺ (3) and Mn²⁺ (5)) are synthesized from bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone (H₄L) using the monometallic precursor complex [MoO₂(H₂L)]·H₂O in ethanol. The composition of the complexes is established based on the data obtained from the elemental analysis and molecular weight determinations. The structure of the complexes is discussed in the light of data obtained from molar conductance, magnetic moment, electronic, EPR and IR spectroscopic studies.     

Reactions of nitrosoarenes containing electron-withdrawing substituents with coordinated CO. Synthesis and structure of complexes Pd2(OAc)2(p-ClC6H4N[p-ClC6H3NO])2 and Pd2(OAc)2(o-ClC6H4N[o-ClC6H3NO])2

The reaction of tetranuclear Pd₄(μ-COOCH₃)₄(μ-CO)₄ cluster (1a) with p- and o-chloronitrosobenzenes was found to give dinuclear nitrosoamide complexes, Pd₂(OAc)₂(p-ClC₆H₄N[p-ClC₆H₃NO])₂ (4) and Pd₂(OAc)₂(o-ClC₆H₄N[o-ClC₆H₃NO])₂ (5), respectively. The formation of complexes 4 and 5 is accompanied by evolution of CO₂, resulting from oxidation of CO coordinated in cluster 1. Complexes 4 and 5 were characterized by elemental analysis and IR and ¹H NMR spectroscopy; their structures were studied by EXAFS. The reactions of dinuclear complex 4 with molecular hydrogen and CO were studied. The major products of reduction of 4 with hydrogen include metallic palladium, acetic acid, cyclohexanone, and molecular nitrogen. Treatment of complex 4 with CO under mild conditions (1 atm, 20 °C) affords p-chlorophenyl isocyanate.     

One-pot microwave-assisted solvent-free synthesis,theoretical and experimental studies on barrier rotation of C–N bond of N-alkenyl-1,2,3-triazoles

The reactions on benzotriazoles continue to happen to reach interesting varieties of their derivatives. This study reports a fast one-pot microwave-assisted solvent-free synthesis of N-alkenyl-1,2,3-benzotriazole (3, 5, and 7) and 1-(2-Alkyloxycarbonyl-vinyl)-1H-[1–3] triazole-4-carboxylic acid methyl ester (8 and 9) derivatives by nucleophilic addition reactions of 1,2,3-benzotriazole (C₆H₅N₃) (1) and 1H-[1–3] triazole-4-carboxylic acid methyl ester (C₄H₄N₃O₂) (1′) with R-propiolates (R = Me, Et; 2 & 4) and phenylacetylene 6 in good yields. The values of activation energy for rotation around C–N bond in the synthesized N-alkenyl-1,2,3-triazole compounds were studied by DFT-B3LYP/6-31G* method.     

3,6-Dialkyl-1-phenyl-6-phenylazo-1,4,5,6-tetrahydropyridazine, (4+2)-Cycloadditionsprodukte aus 2-Phenylazo-1-alkenen, 2. Teil: Reaktionen

Catalytic hydrogenation of 3.6-dialkyl-1-phenyl-6-phenylazo-1.4.5.6-tetrahydropyridazines2 a-e gives crystalline bisphenylhydrazones of 1.4-diketones4 a-e; in solution,4 exists as a mixture of geometrical isomers due to the two phenylhydrazone functions. Reaction of2 a-f with H₂NOH yields the dioximes of 1.4-diketones5 a-f. On acid hydrolysis of2, the 6-phenylazo substituent undergoes some reactions and yields products typical of the intermediate “zwitterionic” phenyldiazene. Thus, the tetrahydropyridazine part of2 d yields 1-anilino-2.5-diisopropyl-pyrrole (9), that of2 e gives 2.2.7.7-tetramethyl-3.6-octanedione monophenylhydrazone (10) which undergoes ready oxidation to 3.6-di-t-butyl-6-phenylazo-1.2-dioxan-3-ol (12).     

Reactivity and reaction pathways of alkylalkoxybenzene radical cations. Part 3. Effects of 2-alkyl substituents on the relative importance of ring-substitution over deprotonation of 2-alkyl-1,4-dimethoxybenzene radical cations

One-electron oxidation of 2-alkyl-1,4-dimethoxybenzenes 1a-f (2-alkyl=Me, Et, i-Pr, cy-C₃H₅CH₂, PhCH₂ and t-Bu) by 4-nitrobenzoyl peroxide 2 and pentaflurobenzoyl peroxide 3 was proved by the observation of great acceleration of decomposition of the peroxides at room temperature, the detection of the corresponding radical cations 1 ^+? a-f and product analysis. The product studies have disclosed that under the conditions employed (in acetonitrile at 40°C), the reaction pathways of the radical cations are greatly dependent on the nature of 2-alkyl substituents: Ring-4-nitrobenzoloxylation product at C ₅ and C ₆ were obtained exclusively in the reactions of the donors with aliphatic 2-alkyl substituents bearing at least one α-hydrogen atom, such as 1a, 1b, 1c and 1d; whereas in the case of 1e (with 2-benzyl group), both ring-substitution at C ₅ (4e) and C ₆ (5e) and deprotonation/4-nitrobenzoloxylation products 8e were isolated; from the donor without α-hydrogen atom, 1f, de-t-butylation products 12 and t-butyl 4-nitrobenzoate 13 were incorporated with ring-substitution at C ₅ (4f) and C ₆ (5f). Furthermore, the product distribution (4 over 5) is also affected by the bulkiness of 2-alkyl group. For all the electron-transfer reactions, large amounts of the benzoic acid (4-NO₂-C₆H₄COOH or C₆F₅COOH) were generated and trace amounts of de-methylation product (2-alkyl-1,4-benzoqinones 6) were also detected by ¹H NMR.     

Evaluation of catalytic activity of imidazolo[1,2-a]pyridine derivatives: oxidation of catechol

A series of heterocyclic compounds possessing imidazolo[1,2-a]pyridine moiety, namely, ethyl 7-methylimidazolo[1,2-a] pyridine-2-carboxylate L1; 2-(3-nitrophenyl)imidazo[1,2-a]pyridine L2; 3-(imidazo[1,2-a]pyridine-2-yl)aniline L3; 2-phenylimidazolo[1,2-a]pyridine-3carbaldehyde L4; and 2-phenylimidazo[1,2-a]pyridine L5 were synthesized. The in situ generated copper (II), iron (II), and zinc (II) complexes of these compounds (L1–L5) were examined for their catalytic activities and were found to be effective catalysts for the oxidation of catechol to o-quinone with the atmospheric oxygen. The present study reveals that the rate of oxidation depends on four parameters: the nature of the ligand, transition metals, ion salts, and the concentration of the complex. The combination L2(Cu(CH ₃ COO) ₂ ) gives the highest rate.     

Oxidation of sulfides with hydrogen peroxide catalyzed by synthetic flavin adducts with dendritic bis(acylamino)pyridines

The catalytic activities of the cationic synthetic flavin adduct 1 with various dendritic and non-dendritic 2,6-bis(acylamino)pyridines 2 were examined for the oxidation of organic sulfides with H₂O₂. The adduct of 5-ethyllumiflavinium perchlorate 1a with 2b–d bearing poly(benzyl ether) dendron units acts as an efficient organocatalyst for the oxidative transformation of sulfides to the corresponding sulfoxides under mild conditions.     

Formation of carbon-carbon bonds between activated alkynes and diimine ligands in the aluminum complexes

The gallium and aluminum complexes containing the redox-active ligand (dpp-bian)Ga-Ga(dpp-bian) (1), (dpp-bian)Al-Al(dpp-bian) (2), or (dpp-bian)AlI(Et₂O) (3) (dpp-bian is 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) react with alkyl butynoates Me-C≡C-CO₂R (R = Me, Et) to form C-C bonds between the dpp-bian ligand and alkyne. The reaction of complex 1 with methyl 2-butynoate and 4-chloroaniline in a molar ratio of 1: 2: 2 affords 7-(2,6-diisopropylphenyl)-10-methylacenaphtho[1,2-b]pyridin-8(7H)-one (4) containing no gallium. In the reaction of complex 2 with methyl 2-butynoate, alkyne is inserted into the skeleton of the dpp-bian ligand to form 4-(dpp-AIE)-9-(2,6-diisopropylphenyl)-8-(1,3-dpp-2MBIDP)-3,7-dimethoxy-1,5-dialuma-9-aza-2,6-dioxabicyclo[3.3.1]nonadiene-3,7 (5) (dpp-AIE is 1-[2-(2,6-diisopropylphenylimino)acenaphthen-1(2H)-ylidene]ethyl; 1,3-dpp-2MBIDP is 1,3-bis(2,6-diisopropylphenylimino)-2-methyl-2,3-dihydro-1H-phenalen-2-yl). The reactions of complex 3 with methyl and ethyl 2-butynoates afford dimeric derivatives [-OC(OR)=C(2,3-dpp-1MBIDP)Al(I)-]₂ (2,3-dpp-1MBIDP is 2,3-bis(2,6-diisopropylphenylimino)-1-methyl-2,3-dihydro-1H-phenalen-2-yl; R = Me (6), Et (7)). The reaction of complex 3 with methyl 2-butynoate gives the product isomeric to compound 6: [-OC(OCH₃)=C(1,3-dpp-2MBIDP)Al(I)-]₂ (8), which cleaves THF resulting in complex [-OC(OCH₃)=C(1,3-dpp-2MBIDP)Al(OC₄H₈I)-]₂ (9). Complex (dpp-bian)Al(acac) (10), obtained by the reduction of dpp-bian with aluminum in the presence of Al(acac)₃ in diethyl ether at ambient temperature, is inert towards acetylene, phenylacetylene, and alkyl butynoates. Compounds 4–7 and 10 were characterized using IR spectroscopy, and compounds 4, 7, and 10 were additionally characterized by ¹H NMR spectroscopy. The structures of compounds 4–7, 9, and 10 were determined by X-ray diffraction analysis.     

Interaction of platinum and molybdophosphoric heteropoly acid under conditions of catalyst preparation for benzene oxidation to phenol with an O2-H2 gas mixture

The transformations of platinum and a heteropoly acid (HPA) in binary systems prepared from H₂PtCl₆ or H₂PtCl₄ and H₃PMo₁₂O₄₀ were studied using IR and UV-VIS spectroscopy, elemental analysis, XPS, EXAFS, TPR, and HREM. The calcination of platinum chloride with the HPA to 450°C resulted in the formation of a platinum salt of the HPA along with decomposition products (mixture I). The reduction of calcined samples containing Pt: HPA = 1: 1 with hydrogen at 300°C (mixture II) followed by exposure to air resulted in the regeneration of the HPA structure. The resulting solid samples of Pt _1?n ⁰ Pt _n ^II Cl_mO_xH_y) (H_3+p PMo _12?p ^VI Mo _p ^V O₄₀) (III) contained platinum and molybdenum in both oxidized and reduced states. The following association species were isolated from mixtures I and II by dissolving in water: [Pt _n ^II PMo₁₂O₄₀] (I _s) (n = 0.3?0.8) and [Pt _n ⁰ PMo ₁₂ ^red O₄₀] (II _s) (n ≈ 1). Under exposure to air, the solutions of I _s were stable (pH ～2), whereas Pt^met was released from II _s. After the drying of I _s, the solid association species (Pt _n ^II Cl_mO_xH_y). (H₃PMo₁₂O₄₀), where n = 0.3?0.8, m = 0.2?1, and x = 3?0, (I _solid) were obtained. The I _solid/SiO₂ supported samples were prepared by impregnating SiO₂ with a solution of I _s and drying at 100°C. Platinum metal particles of size ～20 Å and a mixed-valence association species of platinum with the HPA were observed after the reduction of I _solid/SiO₂ with hydrogen at 100–250°C. These samples were active in the gas-phase oxidation of benzene to phenol at 180°C with the use of an O₂-H₂-N₂ mixture.     

Synthesis of mono- and binuclear dioxomolybdenum(VI) complexes derived from N(4)-substituted thiosemicarbazones: X-ray crystal structures of [(MoO2L)2], [MoO2Lpy] and [MoO2Lpy]

Four molybdenum(VI) thiosemicarbazonato complexes have been synthesized and characterized. The dinuclear complexes [(MoO₂L¹)₂] (1) and [(MoO₂L²)₂] (3) have been prepared by the reaction of [MoO₂(acac)₂] with 2-hydroxyacetophenone N(4)-cyclohexyl (H₂L¹) and N(4)-phenyl (H₂L²) thiosemicarbazones in alcoholic medium. Mononuclear dioxomolybdenum(VI) complexes of the type [MoO₂L¹py] (2) and [MoO₂L²py] (4) have been prepared by the reaction of 1 or 3 with pyridine (py) in alcoholic medium. In all the complexes, molybdenum is coordinated by two terminal oxo-oxygen atoms, (O_t), oxygen, nitrogen and sulfur atoms from the principal ligand and by an oxygen atom from the second unit in 1, and by a nitrogen atom from pyridine in complexes 2 and 4. All complexes have been spectroscopically characterized. The molecular structures of complexes 1, 2 and 4 have been determined by the single crystal X-ray diffraction method.     

Catecholase activity investigation for pyridazinone- and thiopyridazinone-based ligands

A series of seven heterocyclic compounds based on pyridazinone and thiopyridazinone moieties: 5-(2-chlorobenzyl)-6-methylpyridazin-3-one L1; 5-[(2-chlorobenzyl)hydroxyl)methyl]6-methylpyridazin-3-one L2; 5-(2-chlorobenzyl)-2,6-dimethylpyridazin-3-one L3; 5-(2-chlorobenzyl)-2-(hydroxyethyl)-6-methylpyridazin-3-one L4; ethyl-4-(2-chloro-benzyl)-3-methyl-6-oxopyridazin-1(6H)-yl)acetate L5; 5-(2-chlorobenzyl)-2-(hydroxyethyl)-6-methylpyridazin-3-thione L6, and ethyl-4-(2-chloro-benzyl)-3-methyl-6-thioxopyridazin-1(6H)-yl)acetate L7 were tested for the oxidation of catechol to o-quinone for miming microorganism in the O₂ activation for electrophilic non substituted aromatic. The in situ generated Cu(II), Fe(II) and Zn(II) complexes of these ligands (L1–L7) were examined for such catalytic activities. We found that all these substrates catalyze the oxidation reaction of catechol to o-quinone with the presence of atmospheric dioxygen. The rates of this oxidation depend on two parameters: the nature of the ligand and the nature of ion salts. We found that the combination of L7 [Cu(CH ₃ COO) ₂ ] leads to the fastest catalytic processes.     

Copper complexes of two isomeric NS2-macrocycles

Two isomeric NS₂-macrocycles incorporating a xylyl group at ortho (o -L) and meta (m -L) positions were employed and their copper complexes (1?C5) were prepared and structurally characterized. The copper(II) nitrate complexes [Cu(L)(NO₃)₂] (1: L = o -L, 2: L = m -L) for both ligands were isolated. In each case, the copper center is five-coordinated with a distorted square pyramidal geometry. Despite the overall geometrical similarity, 1 and 2 show the different ligand conformation due to the discriminated packing pattern. Reaction of o -L with copper(II) perchlorate afforded complex 3 containing two independent complex cations [Cu(o -L)(H₂O)(DMF)(ClO₄)]⁺ and [Cu(o -L)(H₂O)(DMF)]²⁺; the coordination geometry of the former is a distorted octahedron while the latter shows a distorted square pyramidal arrangement. In the reactions of copper(I) halides (I or Br), o -L gave a mononuclear complex [Cu(o-L)I] (4) with a distorted tetrahedral geometry, while m -L afforded a unique exodentate 2:1 (ligand-to-metal) complex [trans-Br₂Cu(m-L)₂] (5) adopting a trans-type square-planar arrangement.     

Synthesis,crystal structure,and electrochemical properties of Ni(II) and Cu(II) complexes with two unsymmetrical N2O2 Schiff base ligands

Nickel(II) and copper(II) complexes of two unsymmetrical tetradentate Schiff base ligands [Ni(Me-salabza)] (1), [Cu(Me-salabza)] (2) and [Ni(salabza)] (3), {H₂salabza = N,N′-bis[(salicylidene)-2-aminobenzylamine] and H₂Me-salabza = N,N′-bis[(methylsalicylidene)-2-aminobenzylamine]}, have been synthesized and characterized by elemental analysis and spectroscopic methods. The crystal structures of 2 and 3 complexes have been determined by single crystal X-ray diffraction. Both copper(II) and nickel(II) ions adopt a distorted square planar geometry in [Cu(Me-salabza)] and [Ni(salabza)] complexes. The cyclic voltammetric studies of these complexes in dichloromethane indicate the electronic effects of the methyl groups on redox potential.     

Synthesis,crystal structures,luminescence and catalytic properties of three silver(I) coordination polymers with bis(imidazole) and benzenedicarboxylic acid ligands

Three new silver coordination compounds with empirical formula [Ag₂(L1)₂·(ntp)·(H₂O)_3.25]_n (1), [Ag_1.5(L1)_1.5·(H_0.5bdc)·(H₂O)₄]_n (2) and [Ag(L2)(Hmip)]_n (3) (L1 = 1,4-bis(imidazol-1-ylmethyl)benzene, L2 = 1,1′-(1,4-butanediyl)bis-1H-benzimidazole, H₂ntp = 2-nitroterephthalic acid, H₂bdc = 1,3-benzenedicarboxylic acid, H₂mip = 5-methylisophthalic acid) were synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction and physico-chemical spectroscopic methods. The silver centers display different environments with a linear geometry in 1 and 2 and distorted T-shaped geometry in 3. In 1–3, the bidentate N-donor ligands (L1 and L2) bridge neighboring silver centers to form 1D infinite chain structures. Complexes 2 and 3 are extended into 2D layers, and 1 is packed into a 3D 3,4,4,6-connected supermolecular network via classical O–H···O hydrogen bonds, while 3 is further extended into 3D framework through π–π interactions. The luminescence properties of complexes 1, 2 and 3 were investigated in the solid state. These coordination polymers possess a remarkable activity for degradation of methyl orange by persulfate in a Fenton-like process.     

Carbohydrate recognition of symmetrical tripodal receptor type tris(2-aminoethyl)amine derivatives

Carbohydrate recognition of some bioactive symmetrical tripodal receptor type tris(2-aminoethyl)amine (TAEA) derivatives was investigated. In calorimetric experiments, the highest binding constant (Ka) of compound C (C₃₅H₄₉N₅O₄S) with methyl α-d-mannopyranoside was Ka = 858 M^?1 with 1:1 stoichiometry. Formation of hydrogen bonds in binding between symmetrical tripodal receptor type compound C and sugars was suggested by the large negative values of ?H° (=?34 to ?511 kJ mol^?1). In a comparison of each set of α- and β-anomers of some monosaccharides (methyl α/β-d-galactopyranoside, methyl α/β-d-glucopyranoside, and methyl α/β-l-fucopyranoside), compound C showed that the binding constant of β-anomer was larger than that of the corresponding α-anomer, indicating higher β-anomer selectivity. The calculated energy-minimized structure of the complex of compound C with guest methyl α-d-mannopyranoside is also presented. The experimental results obtained from this work indicated that symmetrical tripodal receptor type TAEA derivative C has a lectin-like carbohydrate recognition property.     

Nitric acid in the presence of supported P2O5 on silica gel: an efficient and novel reagent for oxidation of sulfides to the corresponding sulfoxides

This paper describes an efficient and easy method for oxidation of sulfides 1 to their corresponding sulfoxides 2 with nitric acid in the presence of supported P₂O₅ on silica gel under solvent-free conditions in high yields.     

Nucleophilic Attack on an Electronically Unsaturated Triosmium Cluster Complex of 2-Methylbenzoxazole: An Unusual Oxidative Ring Opening

In the course of our studies of nucleophilic attack on electronically unsaturated benzoheterocycle triosmium clusters we have studied the reaction of the 2-methylbenzoxazole complex (μ-H)Os₃(CO)₉(μ₃-η²-2-CH₃–C₇H₃NO) (1) with hydride followed by protonation with acid. In sharp contrast to our previous studies with related benzoheterocycle triosmium clusters, where the nature of the heterocycle controls the regiochemistry of nucleophilic attack, we observe here an unusual ring opening of the heterocyclic ring, coupled with rearrangement of the carbocyclic ring to a 2-imino-ethyl-phenol complex (μ-H)Os₃(CO)₉(μ₃-η³-N=CHCH₃–C₆H₃(OH)) (2). Deuterium labeling experiments verify initial attack by hydride at the 2-position followed by protonation at oxygen. Reaction of 1 with two equivalents of hydride followed by two equivalents of acid results in reduction of the C=N bond in 2 and on standing in air, oxidation of the carbocyclic ring occurs to give the 2-ethyl-amino hydroquinolyl derivative (μ-H)Os₃(CO)₉(μ₃-η³-NHCH₂CH₃–C₆H₃(2-O)(5-OH)) (3). The solid-state structure of 3 is reported and a plausible mechanism, supported by deuterium labeling experiments, is presented, for the formation of 2 and 3.