Metal-free tetra-n-butylammonium bromide-mediated aerobic oxidative synthesis of β-ketosulfones from styrenes

An efficient and broadly applicable protocol for the aerobic coupling of styrenes with sulfonylhydrazides has been developed that affords P-ketosulfones bearing various functional groups in moderate to excellent yields.The preliminary experimental results support the involvement of active benzyl radical species,and a radical pathway was therefore proposed for the reaction.     

Brønsted acid-promoted cyclizations of siloxyalkynes with arenes and alkenes

We have described the first Br?nsted acid-mediated cyclizations of siloxyalkynes with simple arenes and alkenes to afford substituted tetralone and cyclohexenone derivatives. The most notable aspect of the carbocyclizations involving siloxyalkynes is the ability to employ a range of substrates that are not restricted to those containing electron-rich arenes and alkenes. The key mechanistic feature of the reaction is the generation of a highly reactive ketenium ion upon protonation of siloxyalkyne. We believe that the low nucleophilicty of the counteranion is crucial for enabling the formation and effective interception of this highly reactive intermediate.     

New conjugates of β-cyclodextrin with manganese(III) salophen and porphyrin complexes as antioxidant systems

Oxidative stress is the hallmark of several pathologies like arthritis, hypertension and many neurodegenerative disorders such as Parkinson's and Alzheimer's diseases. In this scenario, antioxidant compounds can play a pivotal role in treating these severe pathologies. The synthesis of molecules able to mimic physiologically-relevant proteins is nowadays of particular interest. Several transition metal complexes, especially manganese(III) complexes with porphyrin and salen-type ligands, have been reported to be superoxide scavengers. Here we report the synthesis and spectroscopic characterization of manganese(III) complexes of 5[4-(6-O-β-cyclodextrin)-phenyl],10,15,20-tri(4-hydroxyphenyl)-porphyrin and of 6(A)-deoxy-6(A)[(S-cysteamidobenzoyl(3,4-diamino)-N,N'-bis(salicylidene))]-β-cyclodextrin. The superoxide dismutase activity of the metal complexes was investigated by indirect methods. The catalase and peroxidase activities were tested using ABTS assays.     

Visible-light-promoted oxidative difunctionalization of alkenes with sulfonyl chlorides to access β-keto sulfones under aerobic conditions

A mild, practical and efficient strategy to prepare β-keto sulfones has been developed by visible light promoted reactions. This reaction involves Ir(ppy)₂(dtbbpy)PF₆ catalyzed direct funcationalization of alkenes with sulfonyl chlorides under mild conditions. Air was used as oxidant without any additives. The transformation affords the corresponding products in moderate to high yields.     

The reactions of phosphorus(III) halides with β-diketiminato ligands

Reactions of the lithium or sodium salt, [HC(CMeNDipp)₂]M (Dipp = 2,6-diisopropylbenzene, M = Li or Na), with PBr₃ or PCl₃ affords a series of phosphenium cations that were characterized in the solid state by X-ray crystallography. Solid-state analysis reveals that for compounds 1 and 2, C–H activation of the ligand occurs and the phosphorus is bound to a nitrogen and carbon atom of the ligand. Compound 3 exhibits the more traditional nitrogen chelation of the ligand to the phosphorus atom.     

Kinetics and mechanism of oxidation of α,β-unsaturated alcohols by manganese(III) acetate in aqueous sulphuric acid medium

Summary The kinetics of oxidation of ,-unsaturated alcohols (UA's), such as prop-2-ene-1-ol, but-2-ene-1-ol and 3-phenyl-prop-2-ene-1-ol, by manganese(III) acetate in aqueous H₂SO₄ at constant ionic strength and different acidities has been studied. The reaction was found to proceed through an outer sphere mechanism. The reactions were first order with respect to [Mn^III] and fractional order in [UA]. The reaction showed first order dependence in [H⁺], and the rate decreased on addition of [Mn^II]. Added salts, such as Na₂SO₄, had a negligible effect on the rate. The data suggested that disproportionation of the Mn^III-UA complex into free radicals was the rate determining step in the presence of [Mn^II]. A mechanism consistent with the experimental data is proposed. The activation parameters have been evaluated for the temperature range 298–313 K.     

New rhenium(III) complexes with fluorinated β-diketones

Five new rhenium(III) complexes of the general formula ReCl₂(R_FCOCHCOR_F)(PPh₃)(OPPh₃), where R_F = CF₃ (I), C₂F₅ (II), C₃F₇ (III), C₄F₉ (IV), and CF₃CFOC₃F₇ (V), were synthesized. The known rhenium(V) complex ReOCl₂(OC₂H₅)(PPh₃)₂, which can readily be obtained from metallic rhenium, was used as a precursor. Two polymorphous modifications of compound I were found and studied by X-ray diffraction analysis. The thermal properties of the synthesized complexes were characterized by the DTA-TG method.     

Raman spectra of crystals of some β-diketonates Al(III), Ga(III) and In(III)

Raman spectra of crystals of some metal β-diketonates of the third group have been obtained in the region of 10–3100 cm⁻¹. The polarized spectra of oriented crystals and solutions of chelates in chloroform have been measured. The factor group analysis, polarized spectra and results of deuteration of the chelates showed that all the spectra were divided into two regions: low-frequency 10–100 cm⁻¹ (external vibrations) and high-frequency 100–3100 cm⁻¹ (internal vibrations). In their turn the external modes were divided into translational and librational. The common analysis of the internal vibration behaviour in a series of metals and ligands has been carried out. The torsional vibrations of methyl groups have been interpreted.     

Mechanochemical synthesis of vanadium(III) β-diketonates

The effect of the mechanical treatment conditions and of the nature of reactants on the course of the solid-phase reaction of vanadium(III) chloride with sodium β-diketonates and potassium tetramethylheptanedionate, on the yield of the reaction products, and on some properties of the activated mixtures was examined. A method was developed for the synthesis of vanadium(III) β-diketonates by the solid-phase mechanochemical reaction of vanadium(III) chloride with appropriate sodium or potassium β-diketonate, followed by sublimation or extraction.     

Sensitization of europium(III) luminescence in water with β-diketone-poly(ethylene glycol) macroligand

Poly(ethylene glycol)-modified-diketone macroligand is developed to sensitize europium(Ⅲ)ions in water.High luminescence intensity characteristic of Eu3+ was achieved due to spontaneous formation of micelle-like structure in which the hydrophobic core prevents luminescence-quenching by water molecules.The pH is found to induce a quantitative ratio change in two fluorescence bands from both ligand and Eu3+.     

Crystal structure of a cyanide-bridged heptanuclear manganese(III)–chromium(III) complex with a ground state S = 21/2

K₃[Cr(CN)₆] reacts with the mononuclear Mn^III complex Mn(salen)ClO₄ · 2H₂O [salen: N,N-ethylenebis(salicylideneiminato)dianion] to give a bimetallic heptanuclear complex cation salt [Cr{(CN)Mn(salen · H₂O)}₆][Cr(CN)₆]6H₂O. In the complex anion, [Cr{(CN)Mn(salen · H₂O)}₆]³⁺, six Mn^III ions coordinate to a Cr^III center via cyano bridges, forming a spherical species with 3 symmetry. A study of magnetic properties shows the presence of antiferromagnetic interaction through the cyanide bridge between Cr^III (S = 3/2) and Mn^III (S = 4/2) and results in a ground state S = 21/2.     

Synthesis of β-aminovinylphosphonates by organocatalytic nucleophilic displacement of acetate with amines

The synthesis of diethyl β-aminovinylphosphonates 2 from acetoxy phosphonate 1 is described. The reaction entails an organocatalyzed substitution of the acetoxy group by primary or secondary amines. The use of a catalytic amount of DABCO is necessary if the amine is not nucleophilic enough, otherwise a strong nucleophilic amine can react without organocatalyst. The reaction led to a series of functionalized title compounds in good to excellent yields.     

Spectroscopic Study of Cobalt(III) β-Aminoethylate Complexes

Aqueous solutions of fac- and mer-isomers of [Co(NH₂C₂H₄O)₃] · 3H₂O were investigated by the ¹³C NMR spectroscopy method. The spectrum of the fac-isomer exhibited only two signals with 47.08 (C_N) and 63.87 (C_O) ppm, which points to a high symmetry of the compound and to the presence of a complex in the solution (unlike the crystal) with one type of polyhedron (probably, of a trigonal-prismatic type). The spectrum of the mer-isomer solution is more complicated: the C_Nand C_Osignals are split into three components with 48.81, 47.18, and 46.11 ppm and 64.70, 64.45, and 64.23 ppm, respectively. This fact confirms deterioration of the symmetry of the coordination polyhedron due to nonequivalence of -aminoethylate ions bound to the central atom. The successive protonation of the complexes does not affect either the symmetry of the coordination sphere of the fac-isomer or the asymmetry of the coordination sphere of the mer-isomer. The ¹H, ¹³C, ⁵⁹Co NMR and IR spectroscopy data made it possible to suggest that both fac-[Co(NH₂C₂H₄O)₃] fragments in the binuclear fac-[H₃(Co(NH₂C₂H₄O)₃)₂](NO₃)₃complex are linked together by three symmetrical hydrogen bridges.     

Exploring the reactions of β-amyloid (Aβ) peptide 1-28 with Al(III) and Fe(III) ions

The reactions of human β-amyloid peptide 1-28 (Aβ28) with Al(III) and Fe(III) ions were investigated by (1)H NMR and electrospray ionization mass spectrometry (ESI-MS) under pH conditions close to physiological ones. (1)H NMR titrations, performed in the 5.3-8.0 pH range, revealed that no measurable amounts of Aβ28-Al(III) or Aβ28-Fe(III) adducts are formed; such metal adducts could not be obtained even by changing a number of experimental conditions, e.g., temperature, buffer, nature of the salt, etc. These observations were later confirmed by ESI-MS. It is thus demonstrated that Aβ28, at physiological pH, is not able to form binary complexes with Al(III) and Fe(III) ions of sufficient stability to compete with metal hydroxide precipitation. The biological implications of these findings are discussed in the frame of current literature.     

Liquid secondary ion mass spectrometry of several β-diketonates of cobalt(III) and chromium(III)

The positive, liquid secondary ion (LSI) mass spectra of six cobalt(III) and three chromium(III) (β-diketonates ligand = L^?) were examined in a 3-nitrobenzyl alcohol matrix. The complexes of both metals yield clean, matrix-free mass spectra, but there are important differences between them. The cobalt compounds show prominent peaks assignable to the molecular ion, CoL ₃ ⁺ , of the monomeric chelates, together with abundant dimeric ions, such as Co₂L ₄ ⁺ and Co₂L ₃ ⁺ ; in contrast, chromium complexes show protonated monomers, CrL₃H⁺, in addition to ionized monomers, CrL ₃ ⁺ , and only minor formation of dimeric ions. The collisionally-activated dissociation (CAD) mass spectrum of Co₂L ₄ ⁺ shows fragmentation to CoL ₂ ⁺ and Co₂L ₃ ⁺ . That of Co₂L ₃ ⁺ shows fragmentation only to dimeric ions, including Co₂L ₂ ⁺ and, for thienyl or phenyl substituted ligands, to Co₂L₂Ar⁺ or Co₂LAr⁺ (Ar = thienyl or phenyl). Neither Co₂L ₄ ⁺ nor Co₂L ₃ ⁺ dissociates to the CoL ₃ ⁺ ion. The LSI mass spectrum of a mixture of two different cobalt chelates shows dimeric ions containing both types of ligand, which can be explained by ion-molecule reactions in the selvedge region. The differing behaviors of the cobalt and chromium complexes is attributed to the relatively greater stability of the +2 oxidation state for cobalt than for chromium.     

Extraction chromatographic study of aluminium(III) and mutual separation of aluminium(III), gallium(III), indium(III) and thallium(III) with N-n-octylaniline

A selective method has been developed for extraction chromatographic studies of aluminium(III) and its separation from several metal ions with a chromatographic column containing N-n-octylaniline (liquid anion exchanger) coated on silanized silica gel as a stationary phase. The aluminium(III) was quantitatively extracted with the 0.065 mol/L N-n-octylaninine from 0.013 to 0.05 mol/L sodium succinate at a flow rate of 1.0 mL/min. The extracted metal ion has been recovered by eluting with 25.0 mL of 0.05 mol/L hydrochloric acid and estimated spectrophotometrically with aurintricarboxylic acid. The effects of the acid concentration, the reagent concentration, the flow rate and the eluting agents have been investigated. The log-log plots of distribution coefficient (KdAl(III)) versus N-n-octylaniline concentrationin 0.005 and 0.007 mol/L sodium succinate gave theslopes 0.5 and 0.7 respectively and showed theprobable composition of theextracted species was 1:1 (metal to amine ratio) and the nature of extracted species is [RR''NH2+ Al succinate2-] org. .The extraction of aluminium(III) was carried out in the presence of various ions to ascertain the tolerance limit of individual ions. Aluminium(III) has been separated from multicomponent mixtures, pharmaceutical samples and synthetic mixtures corresponding to alloys. A scheme for mutual separation of aluminium(III), indium(III), gallium(III) and thallium(III) has been developed by using suitable masking agents. The method is fast, accurate and precise.     

Reactions of areneselenenamides with alkenes in the presence of phosphorus(V) and sulfur(IV) oxyhalides. New synthesis of β-haloalkyl selenides

A new procedure was proposed for activation of areneselenenamides with phosphorus(V) and sulfur(IV) oxyhalides. According to the ¹H, ¹³C, and ³¹P NMR data, areneselenenamide reacts with phosphorus oxyhalide to form intermediate adduct in which the phosphorus atom is coordinated at the selenium. Areneselenenamides activated by phosphorus(V) oxyhalides react with alkenes (norbornene and norbornadiene) with high trans-stereoselectivity. Their reactions with terminal olefins are regioselective, and they lead to preferential formation of the corresponding Markovnikov adducts.     

Electrochemical Synthesis of β-Diketonates of La(III) in Ethanol

The electrochemical dissolution of metallic lanthanum in ethanol (EtOH) is studied in the presence of 0.5 M lithium chloride with acetylacetone (HAA), dibenzoylmethane (HDBM), tenoyltrifluoroacetone (HTTA), and benzoylacetone (HBA). Adducts of lanthanum tris--diketonates, specifically, La(AA)₃ · 0.5EtOH, · La(DBM)₃· 2EtOH, La(TTA)₃ · 1.5EtOH, and La(BA)₃ · EtOH are extracted from solution. Electrooxidation of lanthanum during electrolysis is accompanied by its chemical dissolution. The composition of the obtained compounds is confirmed by IR spectroscopy, thermogravimetry, isothermic heating, and elemental analysis for the metal.     

Synthesis,properties and crystal structures of volatile dimethylgold(III) complexes based on phenyl-containing β-diketones and β-iminoketone

We have synthesized and studied volatile dimethylgold(III) complexes based on phenyl-containing β-diketones and β-iminoketone, namely (CH₃)₂Au(C₆H₅–CO–CH–CO–CH₃), (CH₃)₂Au(bac) (1); (CH₃)₂Au(C₆H₅–CO–CH–CO–CF₃), (CH₃)₂Au(btfa) (2); and (CH₃)₂Au(C₆H₅–CO–CH–C(NH)–CH₃), (CH₃)₂Au(i-bac) (3). The obtained compounds were identified by elemental analysis, ¹H NMR and IR-spectroscopy, and were characterized by DTA and single-crystal X-ray diffraction studies. In compounds 2 and 3, the Au atom has a square coordination environment AuC₂O₂ and AuC₂NO, respectively.