Vanadium complexes with quadridentate Schiff bases

The Schiff base ligands N,N′-(±)-trans-bis(3,5-dichloro-2-hydroxyacetophenone)-1,2-cyclohexanediamine (H₂L¹) and N,N′-(±)-trans-bis(5-chloro-4-methyl-2-hydroxyacetophenone)-1,2-cyclohexanediamine (H₂L²) were derived from the condensation of trans-1,2-diaminocyclohexane with 3,5-dichloro-2-hydroxyacetophenone or 5-chloro-4-methyl-2-hydroxyacetophenone, respectively. Both these ligands formed well-defined complexes with vanadium (IV) and (V) under suitable experimental conditions. These complexes have been characterized by elemental analysis, molar conductivity, magnetic moments, infrared, electronic spectra, ESR, X-ray diffraction, and thermogravimetric analysis. X-ray diffraction study of [VO(L²)]·H₂O complex indicated its monoclinic crystal system with a = 9.8525, b = 23.6271, c = 9.0904 Å, and β = 97.87°. The complexes [VO(L¹)]·H₂O and [VO(L²)]·H₂O have been examined as catalysts for epoxidation of styrene in the presence of hydrogen peroxide as oxidant. The IR spectral data suggest that both the ligands behave as dibasic tetradentate chelating agent with ONNO donor atoms sequence toward cental metal ion.     

Alcoxyflurophosphoranes. II—Monoalcoxyfluorophosphoranes possédant un centre d'asymétrie; diastéréotopie des fluors apicaux

Twenty-six monoalkoxyfluorophosphoranes bearing an asymmetric substituent of types R¹PF₃(OR²*)( 1 ), R¹*PF₃(OR²) ( 2 ), R¹R³PF₂(OR²* 3 ) and R₂¹PF₂(OR²*)( 4 ), have been prepared. The non-equivalence of the axial fluorine atoms is observed in the ¹⁹F NMR spectra for the compounds of types 1 δ_F′a – δ_F′a ～ 0·5 to 3·8 ppm, J(F_aF′_a) ～ 10 Hz, 2 δ_Fa – δ_F′a ～ 1·1 to 1·5 ppm, J(F_aF′_a) ～ 14 Hz and 3 δ_Fa – δ_Fa ～ 0·2 ppm, J(F_aF′_a) ～ 10 Hz but not for those of type 4 R₁²PF₂(OR²*). Its origin is assigned to the diastereotopic character of these fluorines. The possibility of a hindered rotation of the substituents as the origin of the phenomenon is excluded. The preparation of sec-BuPF₄ and EtPhPF₃ is also reported.     

Cationic ring-opening polymerization of 3,3-bis（chloromethyl）oxacyclobutane in ionic liquids

Cationic ring-opening polymerization of 3,3-bis(chloromethyl)oxacyclobutane catalyzed by BF_3·OEt_2 was carried out in ionic liquids [bmim]BF_4 and [bmim]PF_6.The influences of BCMO concentration and molar ratio of BCMO/BF_3·OEt_2 on the molecular weights and yield of PBCMO were investigated.The polymerization in ionic liquids proceed to high conversions,although molecular weights are limited,similar to polymerization in organic solvent such as CH_2Cl_2.Follow a viewpoint of green chemistry, we feel ionic liquid [bmim]BF_4 is superior to [bmim]PF_6.Extracting [bmim]PF_6 from the product using organic solvent as extractant limits its advantage as a green reaction media.     

Unexpected retro-Michael reaction of (−)-(1′S,4aS,8aR)- and (+)-(1′S,4aR,8aS)-4a-ethyl-1-(1-phenylethyl)octahydroquinolin-7-ones

An unexpected retro-Michael reaction of (−)-(1′S,4aS,8aR)-and (+)-(1′S,4aR,8aS)-4a-ethyl-1-(1′-phenylethyl)octahydroquinolin-7-ones 1 and 2 is described. In addition, a diastereospecific intramolecular Michael reaction of 3·HCl and 4·HCl is reported.     

Resolution of 1-n-propoxy-3-methyl-3-phospholene 1-oxide by diastereomeric complex formation using TADDOL derivatives and calcium salts of O,O′-dibenzoyl-(2R,3R)- or O,O′-di-p-toluoyl-(2R,3R)-tartaric acid

1-n-Propoxy-3-methyl-3-phospholene 1-oxide was prepared in optically active form by extending resolution methods applying (−)-(4R,5R)-4,5-bis(diphenylhydroxymethyl)-2,2-dimethyldioxolane (‘TADDOL’) and (−)-(2R,3R)-α,α,α′,α′-tetraphenyl-1,4-dioxaspiro[4.5]decan-2,3-dimethanol (‘spiro-TADDOL’), as well as the acidic and neutral Ca²⁺ salts of (−)-O,O′-dibenzoyl- and (−)-O,O′-di-p-toluoyl-(2R,3R)-tartaric acid. In one case, the diastereomeric complex could be identified by single crystal X-ray analysis. The absolute P-configuration of the enantiomers of the phospholene oxide was also determined by CD spectroscopy.     

Chiral Pyrrolidinium Ionic Liquids with (−)-Borneol Fragment in the Cation – Synthesis,Physicochemical Properties and Application in Diels-Alder Reaction

A series of chiral pyrrolidinium salts containing (1 S)-endo-(−)-born-2-yloxymethyl substituent in the structure of the cation and six different anions: chloride, tetrafluoroborate [BF₄]⁻, hexafluorophosphate [PF₆]⁻, trifluoromethanesulfonate [OTf]⁻, bis(trifluoromethylsulfonyl)imide [NTf₂]⁻, bis(pentafluoroethylsulfonyl)imide [NPf₂]⁻ and perfluorobutanesulfonate [C₄FS]⁻ were efficiently prepared and extensively characterized. The enantiomeric purity of them was confirmed by NMR analysis with a chemical shift reagent. All salts were characterized with the specific rotation, the solubility in commonly used solvents, thermal properties, including phase transition temperatures and thermal stability. Salts with [PF₆]⁻, [C₄FS]⁻, [NTf₂]⁻ and [NPf₂]⁻ anions were classified as chiral ionic liquids (CILs). Moreover, salts with [NTf₂]⁻ and [NPf₂]⁻ anions were in the liquid state at room temperature and below. Therefore, density and dynamic viscosity, the surface tension and the contact angle on three different surfaces were also measured for them. Additionally, these chiral ionic liquids were tested as solvents in Diels-Alder reaction.     

Self-Assembly of a Redox Active,Metallosupramolecular [Pd3L6]6+ Complex Using a Rotationally Flexible Ferrocene Ligand

A new ferrocene-containing [Pd₃( L_4EFc )₆]⁶⁺(X⁻)₆ ( C ⋅ BF₄ and C ⋅ SbF₆ where X=BF₄⁻ or SbF₆⁻) self-assembled double-walled triangle has been synthesized from the known, rotationally flexible, 1,1′-bis(4-pyridylethynyl)ferrocene ligand ( L_4EFc ), and characterized by ¹H, ¹³C and diffusion ordered (DOSY) NMR spectroscopies, high-resolution electrospray ionization mass spectrometry (HR−ESI−MS), X-ray crystallography and cyclic voltammetry (CV). The molecular structures confirmed that double-walled triangle cage systems ( C ⋅ BF₄ and C ⋅ SbF₆ ) were generated. C ⋅ BF₄ was shown to interact with the anionic guest, p-toluenesulfonate. CV experiments revealed that the triangles were redox active, however addition of the guest did not influence the redox potentials.     

Temperature dependence of the surface tension and 0.1 MPa density for 1-Cn-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate with n = 2, 4, and 6

Experimental air–liquid interfacial tension data and density data are presented for three 1-C_n-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphates (FAP), [C_nMIM][(C₂F₅)₃PF₃], with n = 2, 4, and 6, measured at atmospheric pressure in the temperature range from 267 K to 360 K using the Krűss K100MK2 tensiometer. The accuracy of the surface tension measurements was checked by employing the Wilhelmy plate and the du Noüy ring methods in parallel. The combined standard uncertainty associated with the Wilhelmy plate method is estimated to be ±0.1 mN · m⁻¹. The density data were obtained using buoyancy method with an estimated standard uncertainty less then ±0.4 kg · m⁻³ (3 · 10⁻⁴ϱ). The chloride anions decrease the density of the tris(pentafluoroethyl)trifluorophosphates of interest up to six times more effectively than they decrease the density of the imidazolium based tetrafluoroborates. A QSPR analysis of the surface tension of imidazolium based ionic liquids with BF₄, TFA, DCA, FAP, NTf₂, and PF₆ anions indicates, that the FAP ionic liquids fit well into the analyzed group of imidazolium based ionic liquids while those having hexafluorophosphate anion show anomalously high deviations of the experimental surface tension from the values predicted by the QSPR model.     

Spectroscopic and structural properties of complexes of 3,3′-bis(2-benzimidazolyl)-2,2′-bipyridine with copper(I) and silver(I)

The pseudo-tetrahedral complexes [CuL₂]PF₆·7H₂O·CH₃OH (1) and [AgL₂]CF₃SO₃·H₂O (2) (L?=?3,3′-bis(2-benzimidazolyl)-2,2′-bipyridine) have been synthesized and characterized through crystal structure analyses, electrochemistry, and spectroscopic methods. X-ray structural analyses of 1 and 2 indicate that sterically constrained N₄ ligands L are cis and behave as bidentate chelates to a single metal ion in a pseudo-tetrahedral fashion through the benzimidazole. As two benzimidazolyl rings exhibit considerable steric hindrance, the bipyridine unit of L remains uncoordinated. The pseudo-tetrahedral cation [CuL₂]⁺ shows a quasi-reversible Cu^I/Cu^II oxidation–reduction wave in the CV in DMF (counter-ion PF₆^?). The fluorescence titration of L with copper(I), silver(I), and also with pH have been conducted to examine the selectivity. The ligand shows remarkably high selectivity and sensitivity for Ag(I).     

Asymmetric reduction of aromatic ketones in pyridinium-based ionic liquids

The asymmetric reduction of aromatic ketones has been studied in pyridinium-based room temperature ionic liquids, namely, 1-ethyl-pyridinium tetrafluoroborate, [EtPy]⁺[BF₄]⁻ and 1-ethyl-pyridinium trifluoroacetate, [EtPy]⁺[CF₃COO]⁻. Ionic liquids were employed as solvents, while (R)-BINOL and (R)-BINOL-Br were used as chiral promoters. The effects of solvent, reaction time, temperature, catalyst loading and substituents were investigated. The reduction could be easily carried out in both ionic liquids with lower catalyst loading. 1-Ethyl-pyridinium tetrafluoroborate was recycled and reused efficiently.     

Ni(dmit)2 salts with chiral stilbazolium- and ferrocenyl-based chromophores as countercations

Four 1:1, two-component salts combining the [Ni(dmit)₂]⁻ anion (dmit²⁻ = 2-thioxo-1,3-dithiole-4,5-dithiolato) and chiral stilbazolium-based countercations (HPMS⁺ = 4′-[2-(hydroxymethyl)pyrrolidinyl]-1-methylstilbazolium and MPMS⁺ = 4′-[2-(methoxy-methyl)pyrrolidinyl]-1-methylstilbazolium), or chiral ferrocenyl-based countercations (2⁺ = (E)-1-((R)-2-methylferrocenyl)-2-(1-methyl-4-pyridiniumyl)ethene; 3⁺ = (E)-1-((S)-2-trimethylsilylferrocenyl)-2-(1-methyl-4-pyridiniumyl)ethene) were prepared. Semiconducting behaviour (2·10⁻⁴ S·cm⁻¹ measured on compressed pellets for [Ni(dmit)₂] (MPMS), for example) is secured by the presence of the [Ni(dmit)₂]⁻ anions. The chiral nature of the countercations ensures non-centrosymmetry of the structures (space group P1 for [Ni(dmit)₂](2) and [Ni(dmit)₂](3), for example). A ubiquitous antiparallel arrangement of the cations, which are thus packed in a pseudo-centrosymmetrical environment, results in almost vanishing second-order susceptibilities χ⁽²⁾, and therefore zero efficiencies in second harmonic generation.     

Role of Mononuclear Rare Earth Metal Complexes in Promoting the Hydrolysis of 2-Hydroxypropyl p-Nitrophenyl Phosphate

Two long-chain multidentate ligands： 2,9-di-（n-2＇,5＇,8＇-triazanonyl）-1,10-phenanthroline （L^1） and 2,9-di- （n-4＇,7＇,10＇-triazaundecyl）-1,10-phenanthroline （L^2） were synthesized. The hydrolytic kinetics of 2-hydroxypropyl p-nitrophenyl phosphate （HPNP） catalyzed by the complexes of L^1 or L^2 with La（Ⅲ） or Gd（Ⅲ） have been studied in aqueous solution at （298.2±0.1） K, I=0.10 mol·dm^-3 KNO3 in pH 7.5-9.1, respectively, finding that the catalytic effect of GdL^1 was the best among the four complexes for hydrolysis of HPNP. Its kLnLH-1, kLnLand pKa are 0.047 mol^-1·L·s^-1, 0.000074 mol^-1·L·s^-1 and 8.90, respectively. This paper expounded the studied result with the structure of the ligands and the properties of the metal ions, and deduced the catalysis mechanism.     

Solubilities of p-coumaric and caffeic acid in ionic liquids and organic solvents

The solubilities of two cinnamic acid derivatives, namely p-coumaric acid and caffeic acid, in six 1-alkyl-3-methyl imidazolium based ionic liquids composed of the PF₆⁻, BF₄⁻, TFO⁻ and TF₂N⁻ anions, and in two organic solvents, t-pentanol and ethyl acetate, have been measured at the temperature range of about (303 to 317) K. The p-coumaric acid was found to be more soluble than caffeic acid in all studied solvents. Higher solubilities of both acids were observed in the ionic liquids composed of the BF₄⁻ and TFO⁻ anions. The increase of the alkyl chain length on the cation invokes a decrease in solubility in the case of hydrophilic ionic liquids composed of BF₄⁻ anion, while in the case of hydrophobic ones composed of PF₆⁻ anion an increase in the solubility is observed. Between the two organic solvents t-pentanol is better solvent than ethyl acetate for both acids. Moreover, using the van’t Hoff equations the apparent Gibbs energy, enthalpy, and entropy of solution were calculated. Finally, successful correlation of the experimental data was achieved with the UNIQUAC and the NRTL activity coefficient models, while poor predictions of the solubility of the two acids in the organic solvents were obtained with two UNIFAC models.     

Synthesis, crystal structures and electrochemical properties of CoIII complexes with hexadentate ligand containing thioether-amidopyridyl donor set

Two new cobalt(III) complexes of the hexadentate ligand [1,4-bis[o-(pyridine-2-carboxamidophenyl)]-1,4-dithiobutane] (H₂bpctb) with N₄S₂ donor set atoms have been synthesized. A reaction of Co(CH₃COO)₂·4H₂O with (H₂bpctb) leads to the formation of [Co^III(bpctb)]PF₆ (1) having a CoN₂(pyridine)N′₂(amide)S₂(thioether) coordination by symmetric bpctb^2? ligand. A similar reaction under slightly different conditions, however, gives [Co^III(L ^a )(L ^b )] (2), resulting from a C–S bond cleavage reaction triggered by an acetate ion as a base, having CoN₂(pyridine)N′₂(amide)S(thioether)S′(thiolate) coordination. These two Co(III) complexes have been characterized by elemental analyses and spectroscopic methods, and the crystal and molecular structures of [Co^III(bpctb)]PF₆ (1) in the form of the solvate (1·MeOH·H₂O) and of [Co^III(L ^a )(L ^b )] (2) have been determined by X-ray crystallography. The Co atoms of both complexes exhibit distorted octahedral geometry. The electrochemical investigation of [Co(bpctb)]PF₆·MeOH·H₂O (1·MeOH·H₂O) and [Co^III(L ^a )(L ^b )] (2) by cyclic voltammetry reveals a reversible Co^III–Co^II redox process at E _1/2 = ?0.32 V (ΔE _p = 80 mV); for 1, and E _1/2 = ?0. 87 V (ΔE _p = 70 mV) for 2.     

BF3-induced cyclobutane-opening of verbenone and its deconjugate homolog. Efficient preparation of o-mentha-1,8-dien-3-one and o-menth-1-en-3-one in optically active forms

Starting with (+)-verbenone, readily obtainable from (+)-nopinone, enantioselective preparation of (S)-(+)-4-isopropenyl-, (S)-(−)-4-isopropyl- and (R)-(+)-4-(1-acetoxy-1-methylethyl)-3-methyl-2-cyclohexen-1-ones was accomplished with little loss of stereochemical integrity via BF₃-induced cyclobutane-opening of (+)-4-(methylene)nopinone. As we have developed an efficient chemical transformation of (+)-nopinone into (−)-verbenone, the present syntheses of the above cyclohexenones are formal syntheses of their enantiomers from (+)-nopinone.     

Development of dispersive liquid-phase microextraction based on new ionic liquid 1,3-diisooctylimidazolium hexafluorophosphate as solvent for the extraction and determination of dicofol and its degradation products in water samples

In the current paper we describe a novel sample preparation technique termed dispersive liquid-phase microextraction for the preconcentration and determination of 2,2,2-trichloro-1,1-bis(4-chlorophenyl)ethanol (dicofol) and its degradation products in water samples that includes 2-(2-chlorophenyl)-2-(4-chlorophenyl)-1,1-dichloroethene(2,4′-DDE), 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane(4,4′-DDE) and 1,1,1-trichloro-2-(2-chlorophenyl)-2-(4-chlorophenyl)ethane (2,4′-DDT) coupled with gas chromatography mass spectrometry (GC-MS), in which a new ionic liquid 1,3-diisooctylimidazolium hexafluorophosphate abbreviated as [D(i-C₈)IM][PF₆] was used as extraction solvent. For each one extraction, 1.00 mL of the methanol solution containing 40 µL of the ionic liquid was sprayed into 25.00 mL of water sample. In the meantime the ionic liquid was finely dispersed into the aqueous phase and analytes were rapidly migrated into the ionic liquid. After the solution was centrifuged for 2 min at 5000 rpm, the droplets of the ionic liquid are subsided in the bottom of the conical test tube (30.0 ± 0.2 µL). Moreover, the factors relevant to extraction efficiencies were investigated and optimised including the volume of the ionic liquid, disperser solvent, extraction time, sample pH and ionic strength. Under optimal conditions, the enrichment factors of the extraction were between 550 and 725 with an extraction efficiency ranging from 66% to 87% for each different analyte. Finally, 1.0 µL of the ionic liquid collected from above extraction was injected into the injector block of GC-MS instrument for analysis. The detection limit (S/N = 3), the relative standard deviations for 2.0 µg L^?1 of the standard analyte (n = 5) and linearity in a calibration range were found to be 3–8 ng L^?1, 1.0–2.7% and 10–3000 ng L^?1, respectively. Good spiked recoveries over the range of 92.0–13.5% were obtained. The proposed method offers the advantages of simplicity of operation, rapidity, good extraction efficiency and enrichment factor; it has been successfully applied to determination of dicofol and its degradation products in environmental water samples.     

Synthesis and applications of (R)- and (S)-7,7′-dimethoxy-2,2′-bis(diphenylphosphino)-1,1′-binaphthalene

The synthesis of (R)- and (S)-7,7′-dimethoxy-2,2′-bis(diphenylphosphino)-1,1′-binaphthalene 5a and 5b is described. The phosphorus atoms in (S)-(−)-5b are shown to be slightly more basic than the phosphorus atoms in (S)-BINAP by comparing the magnitude of the ¹J (³¹P–⁷⁷Se) coupling constant in their respective diselenide derivatives. (S)-(−)-5b behaved similarly to (S)-BINAP in asymmetric Heck reactions.     

Preparation, photophysical, and electrochemical properties of two tetranuclear ruthenium(II) polypyridyl complexes containing 4,5-diazafluorene

Two tetrapodal ligands L¹ and L² containing 4,5-diazafluorene units have been synthesized and characterized. Both ligands are composed of two kinds of nonequivalent coordinating sites: one involves the 4-(4,5-diazafluoren-9-ylimino)phenoxy moiety, and the other one involves the 2-(4,5-diazafluoren-9-ylimino)phenoxy moiety. The Ru(II) complexes [(bpy)₈Ru₄(L¹)](PF₆)₈ and [(bpy)₈Ru₄(L²)](PF₆)₈ (bpy = 2,2′-bipyridine) have been obtained by refluxing Ru(bpy)₂Cl₂·2H₂O and each ligand in 2-methoxyethanol. Both complexes exhibit metal-to-ligand charge transfer (MLCT) absorptions at around 443 nm and emission at around 574 nm. Electrochemical studies of both complexes display one Ru(II)-centered oxidation at around 1.33 V and three ligand-centered reductions.     

Synthesis,structures, and antibacterial activities of two iron(III) complexes with Schiff bases

Two Schiff base iron(III) complexes, [FeL¹(AHA)] · H₂O (I) and [Fe(L²)₂] · ClO₄ (II), where AHA is the deprotonated form of acetohydroxamic acid, and L¹ and L² are the anionic form of N,N′-bis(3-ethoxysalicylidene)propane-1,2-diamine and 2-[1-(2-aminopropylimino)ethyl]phenol, respectively, have been synthesized and characterized by physical chemical methods and single crystal X-ray diffraction. Crystallographic data for I: orthorhombic, space group Iba2, a = 20.781(3), b = 23.527(3), c = 10.071(2) Å, V = 4923.7(12) ų, Z = 8, R ₁ = 0.0374, wR ₂ = 0.0900. Crystallographic data for II: triclinic, space group a = 12.748(1), b = 13.401(1), c = 19.007(1) Å, α = 106.623(2)°, β = 97.462(2)°, γ = 112.543(2)°, V = 2784.9(4) ų, Z = 4, R ₁ = 0.0892, wR ₂ = 0.2434. X-ray crystal structural study indicated that the coordination environment around each Fe atom in the complexes is a six-coordinated distorted octahedron. The antibacterial activities of the complexes were assayed.     

Characterization of copper(II) coordination compounds of 5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine: the crystal structure of diaquatetrakis(5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine-N3)-copper(II) hexafluorophosphate

Copper(II) coordination compounds of several CuA₂ salts (A = PF₆, BF₄, ClO₄, CF₃SO₃ or NO₃) with 5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine (dmtp) as a ligand have been studied. The crystal structure of [Cu(dmtp)₄(H₂O)₂](PF₆)₂ is described. This compound is monoclinic, space group P2₁/c, a = 11.826(2) Å, b = 9.463(2) Å, c = 17.673(3) Å, β = 97.50(1)°, Z = 2, d_calc. = 1.66 Mg m⁻³, and has been refined to a final discrepancy factor (R) of 0.0382 based on 2316 reflections. The structure consists of PF⁻₆ anions and centrosymmetric mononuclear [Cu(dmtp)₄(H₂O)₂]²⁺ cations, Cu₂₊ being coordinated by four equatorial N(3)-bonded dmtp molecules with CuN = 2.019 and 2.050 Å, and by two axial water molecules with CuO = 2.650 Å. The water molecules form intramolecular hydrogen bonds with the dmtp N(4) atoms.