Reactions of tungsten(VI) and molybdenum(V) chlorides,and tungsten(VI) and molybdenum(VI) oxychlorides,with azoxybenzene

Reactions of W^VI and Mo^V chlorides with azoxybenzene yield ionic species of W^VI and Mo^VI oxychlorides in which the cation is a protonated azobenzene. The reaction between MoCl₅ or MoOCl₄ and azoxybenzene gives, after extraction with methylene chloride—ethanol mixture, the complex [trans-MoOCl₄(OC₂H₅)]^? [C₁₂H₁₀N₂H]⁺. In contrast, WOCl₄ reacts with azoxybenzene to give a stable non-ionic adduct in which the organic moiety is coordinated through its oxygen atom trans to the WO bond. Several complexes of substituted azoxybenzene having similar structures are described.     

The relationship of morphology and catalytic performance of CeO_2 catalysts for reducing nitrobenzene to azoxybenzene under the base-free condition

CeO_2 morphology was proposed to be a crucial factor for reducing nitrobenzene to azoxybenzene under the base-free condition.Herein,the structure-activity relationship of CeO_2 catalysts was explored to improve the azoxybenzene yield.A series of CeO_2 catalysts we re synthesized with seven morphologies to obtain different Ce~(3+) proportion and various surface areas.Notably,the catalytic performance of these samples for reducing nitrobenzene to azoxybenzene enhanced with the increasing Ce~(3+) proportio n.With the highest surface Ce~(3+)proportion,the Rod-CeO_2 catalyst exhibited 100% conversion of nitrobenzene and 89.8% azoxybenzene selectivity in 7 h at 150℃ under 1 MPa CO.Moreover,the preliminary mechanistic analysis indicated that the inhabitation of azoxybenzene to by-product azobenzene resulted in the high selectivity of azoxybenzene.     

X-ray crystal structure of azoxybenzene oxotetrachlorotungsten(VI), (C6H5N)2OWVIOCl4

The crystal and molecular structure of azoxybenzene oxotetrachlorotungsten(VI) has been determined from X-ray diffractometer data. The structure was solved by Patterson and Fourier methods and refined by least-squares techniques to R = 0.058 for 1869 independent reflections.The crystals are monoclinic, space group P2₁/c, with Z = 4, in a unit cell of dimensions: a = 8.314(3), b = 15.100(5), c = 12.901(7) Å, α = 95.31(5)°. The azoxybenzene residue, the structure of which resembles that of free trans azobenzene, is linked to the tungsten atom through its oxygen atom. The coordination at the metal (two oxygen atoms and four chlorine atoms) corresponds to a distorted octahedron.This distortion is very similar to those observed in similar tungsten compounds. There is a intramolecular C?O distance of 2.77 Å between two atoms four bonds apart, of the azoxybenzene residue.     

The catalytic transformation of nitrosobenzene into azoxy and azobenzene

Nitrosobenzene is converted into azoxybenzene in alcoholic media in the presence of Ru(CO)₃(PPh₃)₂ as catalyst and under an inert atmosphere; Fe(CO)₃(PPh₃)₂ and palladium complexes such as PdL₂Cl₂ (L  PhNO, p-MeC₆H₄NH₂, PPh₃) and Pd₃(CO)₃(PPh₃)₄, are less active as catalysts. Under CO pressure and with Ru(CO)₃(PPh₃)₂ as catalyst, nitrosobenzene is converted into azobenzene and aniline, while azoxybenzene gives azobenzene.     

Synthesis of allylamides from allyl halides, carbon monoxide, and titanium-nitrogen complexes prepared from molecular nitrogen

4-Phenylbut-3-enamide could be synthesized from corresponding 3-chloroprop-2-enylbenzene, carbon monoxide (1 atm), and titanium-nitrogen complexes, prepared from Ti(OⁱPr)₄, Li, TMSCl, and molecular nitrogen (1 atm), using a palladium catalyst. The reaction proceeds via transmetalation of the titanium-nitrogen complex to an acylpalladium complex. P^tBu₃ as a ligand of the palladium catalyst, afforded a good result, and the amounts of Li and TMSCl affected the yield of amide. When the reaction was carried out using a bidentate ligand on the palladium complex under an atmosphere of argon instead of carbon monoxide, an allylamine derivative was obtained.     

Silver N-heterocyclic carbene complexes as initiators for bulk ring-opening polymerization (ROP) of l-lactides

Synthetic, structural and catalysis studies of two silver complexes namely, {[1-(2,4,6-trimethylphenyl)-3-(N-phenylacetamido)imidazol-2-ylidene]₂Ag}⁺Cl⁻1b, supported over an amido-functionalized N-heterocyclic carbene ligand, and [1-(i-propyl)-3-(benzyl)imidazol-2-ylidene]AgCl 2b, supported over a non-functionalized N-heterocyclic carbene ligand, are reported. Specifically, 1b, a cationic complex bearing 2:1 NHC ligand to metal ratio, was obtained from the reaction of 1-(2,4,6-trimethylphenyl)-3-(N-phenylacetamido)imidazolium chloride 1a with Ag₂O in 52% yield. The corresponding 1a was synthesized by the alkylation reaction of 1-(2,4,6-trimethylphenylimidazole) with N-phenyl chloroacetamide in 73% yield. The other silver complex 2b, a neutral complex bearing 1:1 NHC ligand to metal ratio, was obtained from the reaction of 1-(i-propyl)-3-(benzyl)imidazolium chloride 2a with Ag₂O in 42% yield. The 2a was synthesized by the alkylation reaction of 1-(i-propylimidazole) with benzyl chloride in 45% yield. The molecular structures of the imidazolium chloride, 1a, and the silver complexes, 1b and 2b, have been determined by X-ray diffraction studies. The silver complexes, 1b and 2b, successfully catalyze bulk ring-opening polymerization (ROP) of l-lactides at elevated temperatures under solvent-free melt conditions producing moderate to low molecular weight polylactide polymers having narrow molecular weight distributions.     

Synthesis, structure, electronic properties and thermal behavior of butadiynyl substituted phenylCr(CO)3-complexes

Butadiynyl-substituted η⁶-benzeneCr(CO)₃ complexes 3 are very efficiently prepared by a copper catalyzed coupling of the phenylacetylene complex 1 and bromo alkynes 2. The transmission of electronic effects through the butadiynyl bridge operates by resonance mechanisms as established by correlations between Hammett's σ_p, σ_R and σ_P⁺ parameters. Most interestingly, however, is an unusual thermal behavior that leads to intractable paramagnetic polymers of unknown structure. According to thermal analyses (thermal gravimetrical analysis, differential scanning calorimetry) the complexes 3 react in a thermal solid-state reaction under CO extrusion to give amorphous cross-linked polymers.     

H NMR aided elucidation of products derived from photodegradation of ethyl 3-azido-4,6-difluorobenzoate in 2,2,2-trifluoroethanol

The major products formed upon photolysis of ethyl 3-azido-4,6-difluorobenzoate in 2,2,2-trifluoroethanol-d₃ has been elucidated by ¹H NMR analysis of the product mixture. Among the products formed and structurally elucidated was a hitherto unreported product formed during photolysis of aryl azides, namely azoxybenzene 19. The structural assignments of the major components of the reaction mixture were aided by comparison with ¹H NMR data from synthetic reference materials and compound isolation. MS, MS/MS, and HPLC analysis as well as UV spectroscopy was also employed in order to confirm and aid the structural analysis.     

Trindenyl[tris(rheniumtricarbonyl)]

Trindene is combined with KH and [Re(CO)₃(THF)Br]₂ (THF = tetrahydrofuran) in THF to yield the first trinuclear half-sandwich complex of the trindene trianion, (trindenyl)[Re(CO)₃]₃, in 50% yield. Two of the rhenium carbonyl units are rigidly held in close proximity and the carbonyl ligands on adjacent metals are vibrationally coupled. Both cis and trans isomers of the dirhenium complex, (trindenyl)[Re(CO)₃]₂, are also isolated from the above reaction in low yield.     

Novel 1D coordination polymer {Tm(Piv)3}n: Synthesis,structure, magnetic properties and thermal behavior

The new 1D coordination polymer {Tm(Piv)₃}_n (1), where Piv=OOCBu^t?, was synthesized in high yield (>95%) by the reaction of thulium acetate with pivalic acid in air at 100 °С. According to the X-ray diffraction data, the metal atoms in compound 1 are in an octahedral ligand environment unusual for lanthanides. The magnetic and luminescence properties of polymer 1, it’s the solid-phase thermal decomposition in air and under argon, and the thermal behavior in the temperature range of ?50…+50 °С were investigated. The vaporization process of complex 1 was studied by the Knudsen effusion method combined with mass-spectrometric analysis of the gas-phase composition in the temperature range of 570–680 K.     

Chiral N,N′-dioxide-iron(II) complexes catalyzed enantioselective oxa-Michael addition of α,β-unsaturated aldehydes

The enantioselective oxa-Michael addition reaction of 1-(4-methoxyphenyl) ethanone oxime to various α,β-unsaturated aldehydes was accomplished by using chiral N,N′-dioxide-FeSO₄·7H₂O (1:1) complex. Aromatic acid was employed as additive to increase the yield of the reaction. The corresponding adducts were obtained in moderate yields with up to 76% ee under mild conditions.     

Electrophilic cyclization of 3-alkynyl-4-chalcogen-2-H-chromenes: synthesis of 3-halo-chalcogenophene[3,2-c]chromene derivatives

An efficient synthesis of 3-halo-chalcogenophene[3,2-c]chromene has been accomplished via electrophilic cyclization reaction of 3-alkynyl-4-chalcogen-2H-chromene using I₂, PhSeBr, and BuTeBr₃ as electrophilic sources. The cyclization reaction proceeded cleanly under mild reaction conditions, and 3-halochalcogen-chromenes were formed in good yields. In addition, the obtained 3-iodo-chalcogenophene-chromenes were readily transformed to more complex products using a metal-halogen exchange reaction with n-BuLi and trapping the lithium-intermediate formed with aldehyde, furnishing the desired secondary alcohol in good yield. Conversely, using the palladium catalyzed cross-coupling reactions with terminal alkynes and boronic acid, we were able to obtain the Sonogashira and Suzuki type products in good yields.     

Trifluoromethyl-containing pyrazolinyl (p-tolyl) sulfones: The synthesis and structure of promising antimicrobial agents

The regiospecific synthesis of a novel series of nine 4-phenyl- and 3-alkyl(aryl)-5-hydroxy-5-trifluoromethyl-4,5-dihydro-1H-1-tosylpyrazoles (pyrazolinyl p-tolyl sulfones), as well as their antimicrobial activity against yeast, such as fungi, bacteria, and alga are reported. The 1-p-tosyl-2-pyrazolines were obtained from the cyclocondensation reaction of 3-phenyl- and 4-alkyl(aryl)-1,1,1-trifluoro-4-alkoxy-3-alken-2-ones, [where alkyl = H, Me and aryl are -C₆H₅, 4-CH₃C₆H₄, 4-OCH₃C₆H₄, 4-FC₆H₄, 4-ClC₆H₄, 4-BrC₆H₄,] with p-tosylhydrazine in a yield of 58-92% when toluene was employed as solvent. The best activity was obtained when the structure possessed a 4-fluorophenyl substituent linked at the carbon-3 of the pyrazoline ring. Subsequently, the dehydration reaction of 3-(4-fluorophenyl) substituted 2-pyrazoline with thionyl chloride/pyridine in benzene as solvent furnished the corresponding 1H-pyrazole in only a moderate yield (49%).     

Chemoselectivity control in the reaction of a dinuclear chloro-bridged cyclopalladated complex with potassium diphenylphosphide

Reactions of KPPh₂ with the dimeric cyclopalladated complex {Pd(N∩C)(μ-Cl)}₂1 derived from N,N-dimethylbenzylamine were studied using different reagent ratios, temperature, reaction time, concentrations and solvents. Complex 3, the μ-Cl-μ-PPh₂ analog of 1, was obtained in 76% yield in the one-hour reaction using the 1:1 ratio of dimer 1 and KPPh₂ in THF at rt. ortho-(Diphenylphosphino)benzylamine 4 was synthesized in 58% yield by reacting complex 1 with 4.5 equiv. of KPPh₂ in THF at rt. A possible mechanism of the aminophosphine formation is proposed on the basis of the experimental data including ³¹P{¹H} NMR spectra of reaction mixtures.     

Crystal structure and thermal stability of A μ1,1-(OMe)-bridged dimeric Schiff base iron(III) complex

A new μ_1,1-OMe-bridged dimeric iron(III) complex, [Fe₂L₂(μ_1,1-OMe)₂(NCS)₂], where L is the deprotonated form of 2-[(2-ethylaminoethylimino)methyl]-5-methoxyphenol, has been prepared and structural characterized by elemental analysis, IR spectrum, and single crystal X-ray crystallography. The complex crystallizes in the monoclinic space group P2₁/c, with unit cell dimensions a = 10.156(1) Å, b = 11.972(1) Å, c = 14.256(2) Å, β = 102.643(3)°, V = 1691.3(3) ų, Z = 2, R ₁ = 0.0394, and wR ₂ = 0.0922. Each Fe atom in the complex is in an octahedral coordination. The Fe...Fe distance is 3.102(1) Å. The thermal stability of the complex was studied.     

Reaction of copper(II) cysteinate with thiosemicarbazide: Crystal structure of a complex of copper(II) thiocyanate with thiosemicarbazide

The reaction of copper(II) cysteinate with thiosemicarbazide (TSC) in water was found to yield complex of copper(II) thiocyanate of the [Cu(TSC)₂(SCN)₂] composition, whose crystal structure was determined by X-ray crystallography. Crystals of the complex are triclinic with a = 6.040 Å, b = 7.112 Å, c = 8.276 Å, α = 91.34°, β = 101.72°, Γ = 114.83°, Z = 2, space group \(P\bar 1\). Structural units of the complex are [Cu(TSC)₂]²⁺ centrosymmetric cations and (SCN)^? anions linked by hydrogen bonds (HB), as well as by electrostatic and π-π stacking interactions. The coordination polyhedron of Cu atoms is a square completed to bipyramid; the bonds Cu(1)-N(3), Cu(1)-S(1), and Cu(1)-S(2) are 2.002 Å, 2.303 Å, and 3.015 Å, respectively.     

Combining engineering and chemistry for the selective continuous production of four different oxygenated compounds by photo-oxidation of cyclopentadiene using liquid and supercritical CO2 as solvents

A range of products is reported from the photo-oxidation of cyclopentadiene from photochemically generated singlet oxygen (¹O₂) using carbon dioxide (CO₂) as a solvent and 5,10,15,20-tetrakis-(pentafluorophenyl)porphyrin (TPFPP) as a CO₂-soluble photosensitizer. The endo-peroxide intermediate, generated from the reaction with singlet oxygen, is transformed into one of several different products in good yield depending on the conditions applied and by adding different reactors and reagents downstream of the photo-reactor, allowing the reaction products to be switched in one streamlined process. The addition of a thermal reactor facilitated the rearrangement of the endoperoxide to form Z-4,5-epoxy-2-pentanal. Quenching with thiourea yielded the syn-diol, (1R,3S)-cyclopent-4-ene-1,3-diol. Treatment with acid or base afforded furfuryl alcohol and 4-hydroxy-2-cyclopentenone respectively. High productivities for all products were obtained when compared to traditional batch reactions.     

Structure and properties of tripyridine nitrosocomplexes of ruthenium: mer-[Ru(NO)Py3Cl(OH)]Cl·1.5H2O and mer-[Ru(NO)Py3Cl(H2O)]Cl2·2H2O·0.5HCl

The reaction of K₂[Ru(NO)Cl₅] with pyridine in aqueous ethanol at pH ～ 7–8 affords a nitrosoruthenium hydroxocomplex mer-[Ru(NO)Py₃Cl(OH)]Cl·1.5H₂O (I) (yield ～55%). Treatment of hydroxocomplex I with hydrochloric acid at room temperature gives the aqua complex mer-[Ru(NO)Py₃Cl(H₂O)]Cl₂·2H₂O·0.5HCl (II). The structures of the compounds are determined by X-ray crystallography: I, space group P2₁/n, a = 9.2292(4) Å, b = 11.7781(4) Å, c = 17.4915(7) Å, β = 90.9560(10)°, R = 4.84%; II, space group P-1, a = 7.3528(9) Å, b = 11.5793(11) Å, c = 13.6961(16) Å, α = 84.558(3)°, β = 87.668(4)°, γ = 74.146(4)°, R = 6.22%. Compounds I and II are characterized by powder XRD, ¹H and ¹³C NMR, and IR spectroscopy. The thermal decomposition of compound II in the inert atmosphere is examined by thermal analysis.     

A novel synthesis of organic diselenapolysulfides

A family of organic polychalcogenides with a common structure of RSeS_xSeR (with x=1, 2, 3 and R=CH₃, Ph, PhCH₂, O₂NC₆H₄CH₂) as well as cyclic 5,5-dimethyl-1,2-dithia-3,7-diselenacycloheptane were synthesized in good yield and high purity from the reaction of Ph₃CS_xCl with corresponding diselenides in chloroform at room temperature. Mechanistic aspects of the insertion involving the formation of an intermediate (RSeS_xCPh₃) are discussed.     

Transition metal complexes with pyrazole-based ligands. Part 28. Synthesis,structural, DFT and thermal studies of cadmium(II) halides and zinc(II) chloride complexes with 3,5-dimethylpyrazole-1-carboxamidine

The complex formation of 3,5-dimethylpyrazole-1-carboxamidinium nitrate, HL·HNO₃ with ammine complexes of cadmium(II) halides (Cl, Br, I) and zinc(II) chloride has been investigated under self-controlled reaction conditions. The complexes have been characterized by X-ray diffraction, FT-IR spectroscopy, thermal analysis and quantum chemical calculations. In the case of cadmium bromide and iodide salts, isostructural complexes with composition of [CdX₂(HL)₂] were formed. With CdCl₂ a binuclear octahedral [Cd₂(HL)₄(μ-Cl)₂](NO₃)₂ complex is obtained. Zinc(II) chloride with HL·HNO₃ gives [Zn(HL)₂Cl]NO₃, the zinc center exhibiting severely distorted five-coordinate stereochemistry, intermediate between an ideal trigonal bipyramid and a square pyramid. The course of complex formation as well as the thermal properties of the compounds has been explained using the HSAB principle. The assignment of the FT-IR spectra was supported by DFT computations.