N- and O-arylation with triphenylantimony ortho-phenylenedioxides

2,2,2-Triphenyl-1,3,2-benzodioxastibolanes react with alcohols, phenols, and amines in the presence of copper salts to give the corresponding O- and N-phenyl derivatives. Cyclic Sb^V dialkoxide containing an electron-withdrawing nitro group in the dioxastibolane fragment is most reactive in N-phenylation of primary and secondary amines. Organoantimony analogs containing electron-donating groups are more efficient in O-phenylation of primary and secondary alcohols and phenols.     

Molecular level approach to the origin of the steric control in organozinc catalyst for oxirane polymerization

A new type of single crystals was formed by a reaction between diethylzinc and DL-1-methoxy-2-propanol. The constituent unit of this single crystal was shown to be a two to two complex of zinc dialkoxide and ethylzinc alkoxide, [MeOCH² CH(Me)OZnOCH(Me)CH² OMe]² · [EtZnOCH(Me)CH² OMe]², which has a chair type structure. The two to two complex was found to exhibit higher activity and stereospecificity in the PO polymerization compared with those of the one to six complex which were reported previously. Molecular level elucidation was made on the basis of NMR studies for polymerization system with a partly deuterated two to two complex as initiator. The excellent stereospecificity in isotactic propagation was ascribed to the highly chiral hole around the active site of the chair type complex. Another series of study revealed chemical behavior of cyclohexene oxide (CHO), which is different from that of PO, toward several organozinc compounds. The two to two complex was the only catalyst which showed high activity for both MO and CHO polymerizations. Three samples (I), (II) and (III) of poly-(CHO) were prepared with Et²Zn, EtZnOR and the two to two complex, respectively. After careful examinations of each of the three samples, it was concluded that most parts of the main chain of polymer (III) molecule were composed of syndiotactic triad, SS-RR-SS(or RR-SS-RR), while polymer (I) and (II) molecules contained syndiotactic and heterotactic triads in comparative amounts. In the CHO polymerization, the chiral hole of the two to two complex cannot recognize the mode of orientation of the achiral monomer, and the complex seems to serve as a simple bulky group which facilitates syndiotactic addition of CHO monomer molecule to the active site, strong steric effects being exerted from the penultimate unit of the growing chain during the propagation stage.     

Sensitive spectrofluorimetric determination of zinc at ultra-trace levels

An ultra-trace method based on the reaction of zinc with salicylthiocarbohydrazone (SATCH) and Triton X-100 as a non-ionic surfactant was developed for the fluorimetric determination of zinc at the picogram level. The reaction is carried out in the pH range 4.4–4.7 in an aqueous ethanolic medium [52% (v/v) ethanol]. The influence of the reaction variables is discussed. The detection limit is 10 pg ml^?1 and the range of application is 0.01–500 μg l^?1, with an optimum range of 0.04–400 μg l^?1. The relative standard deviations are 0.68% (0.01–0.1 μg l^?1 of zinc), 0.41% (0.1–1.0 μg l^?1 of zinc), 0.64% (1–10 μg l^?1 of zinc), 0.82% (10–100 μg l^?1 of zinc) and 0.15% (100–500 μg l^?1 of zinc). The method is highly sensitive and selective in the presence of Cd^II and Hg^II. The effect of interferences from other metal ions and anions was studied; the masking action is discussed. The advantages of the proposed method include its high sensitivity, simplicity and selectivity.     

Efficient Oxidation and Destabilization of Zn(Cys)4 Zinc Fingers by Singlet Oxygen

Singlet oxygen (¹O₂) plays an important role in oxidative stress in all types of organisms, most of them being able to mount a defense against this oxidant. Recently, zinc finger proteins have been proposed to be involved in its cellular detection but the molecular basis of this process still remains unknown. We have studied the reactivity of a Zn(Cys)₄ zinc finger with ¹O₂ by combinations of spectroscopic and analytical techniques, focusing on the products formed and the kinetics of the reaction. We report that the cysteines of this zinc finger are oxidized to sulfinates by ¹O₂. The reaction of the ZnS₄ core with ¹O₂ is very fast and efficient with almost no physical quenching of ¹O₂. A drastic (ca. five orders of magnitude) decrease of the Zn²⁺ binding constant was observed upon oxidation. This suggests that the Zn(Cys)₄ zinc finger proteins would release their Zn²⁺ ion and unfold upon reaction with ¹O₂ under cellular conditions and that zinc finger sites are likely targets for ¹O₂.     

Extraction and spectrophotometric determination of zinc in coal fly ash and pond sediments with 2-[2-(3,5-dibromopyridyl)azo]-5-dimethylaminobenzoic acid

An extraction-spectrophotometric method is described for the determination of traces of zinc with 2-[2-(3,5-dibromopyridyl)azo]-5-dimethylaminobenzoic acid. The reagent forms a stable, blue 1:2 zinc/reagent complex that can be extracted into chloroform. The apparent molar absorptivity of the zinc(II) complex is 1.26 × 10⁵ l mol^?1 cm^?1 at 610 nm in chloroform. The reagent is relatively selective; interferences from cobalt, copper and nickel can be masked with dimethylglyoxime and aluminium and iron with a mixture of sodium fluoride and triethanolamine. The method is applied to the determination of zinc in coal fly ash and pond sediments with good precision and accuracy.     

Characterization of neutron transmuted zinc traces in pure copper materials by isotope dilution mass spectrometry

The neutron transmutation doping (NTD) of highly pure copper with zinc was investigated as a promising means of achieving controlled gradation of the zinc content in the range 1–20 μg g^–1. The doping process leads to the enrichment of two stable isotopes ⁶⁴Zn and ⁶⁶Zn in a ratio which differs from that of natural isotopic distribution. Mass spectrometric investigations by thermal ionization mass spectrometry (TIMS) were performed to validate the results obtained by gamma spectrometry. The investigations included both determination of the isotopic ratios of the doped zinc isotopes and the analysis of the accumulated zinc contents by isotope dilution (ID) analysis. Thereby a sample-specific correction of the blank could be performed because the isotope ⁶⁸Zn was not influenced, because of the transmutation process. The results obtained by TIMS prove the strict proportionality of the doped zinc content, in the range 5 to 20 μg g^–1, to the neutron fluence. Comparison with gamma spectrometric results showed a very good agreement within the uncertainties.     

Selective fluorimetric determination of nanogram amounts of zinc in workplace fumes

The very selective fluorogenic reaction of zinc with thiophene-2-aldehyde-2-quinolyl-hydrazone is used to provide a sensitive determination of zinc. The limit of detection is 10 ng ml^?1 and the calibration graph is linear over the range 20–200 ng ml^?1 zinc. The nature of the complex formed and the cause of the high selectivity are discussed. The method has been satisfactorily applied to the determination of zinc in metal fumes collected in workshops.     

Syntheses and Molecular Structures of 2-(1-Methyliminoethyl)phenolato Zinc Complexes

2-(1-Methyliminoethyl)phenol ( 1 a ) reacts with diethyl zinc to give bis[2-(1-methyliminoethyl)phenolato]zinc ( 3 ) via [2-(1-methyliminoethyl)phenolato]ethylzinc ( 2 ) as an intermediate. The complex 3 is also formed in the reaction of bis(trimethylsilyl)amide zinc with 1 a . The compounds were characterized by microanalysis, NMR (¹H, ¹³C) and IR spectroscopy. X-ray structure analysis of the compounds 2 and 3 revealed that both compounds form in the solid state dimeric species where the monomeric units are bridged via two oxygen atoms forming a planar Zn₂O₂ ring with tetrahedral [ZnO₂NC] and trigonal-bipyramidal [ZnO₃N₂] coordination of the zinc atom, respectively.     

A spectrophotometric study of the color reaction of zinc with 2,2′-dipyridyl-2-pyridylhydrazone (DPPH)

A spectrophotometric study of the zinc complex with 2,2′-clipyridyl-2-pyridylhydrazone (DPPH) is presented. The optimal formation conditions, the composition, and the overall apparent instability constant of the yellow, water-soluble zinc — DPPH complex are studied. A simple, rapid, and very sensitive spectrophotometric method for the determination of zinc with DPPH is proposed. At pH 10.9 to 12.4 the molecular extinction coefficient of the complex is 5.25 × 10⁴M⁻¹ · cm⁻¹ at 442 nm. DPPH can be also used as a methallochromic indicator for the complexometric titration of zinc.     

Utilization of a spiropyran derivative in a polymeric film optode for selective fluorescent sensing of zinc ion

Spiropyrans are the most studied families of func- tional materials due to their reversible structural con- version in response to external optical, chemical, and thermal stimulation[1]. Irradiation with ultraviolet light causes formation of an extended π-conjugation open form (merocyanine form) by heterolytic cleavage of the C (spiro)-O bond, which generates an intense ab- sorption in the visible region. Under the irradiating of visible light, the opened form will come back to the closed spi…     

Raman and FTIR Spectroscopic Studies of 1‐Ethyl‐3‐methylimidazolium Trifluoromethylsulfonate,its Mixtures with Water and the Solvation of Zinc Ions

In this paper we report on the interactions of the ionic liquid 1‐ethyl‐3‐methylimidazolium trifluoromethylsulfonate ([EMIm]TfO) with water and the solvation of zinc ions in neat [EMIm]TfO and [EMIm]TfO–water mixtures investigated by FTIR and Raman spectroscopy. The structures and physicochemical properties of the [EMIm]TfO–water mixtures are strongly dependent on the interaction between cations, anions, and water. The structure was changed from ionic‐liquid‐like to water‐like solutions upon addition of water. In addition, zinc salts can precipitate in 0.2 M Zn(TfO)₂/[EMIm]TfO upon addition of 10 % (v/v) water, presumably as a result of polarity change of the solution. The average coordination number of TfO^? per zinc ion calculated from Raman spectra is 3.8 in neat [EMIm]TfO, indicating that [Zn(TfO)₄]^2?, and [Zn(TfO)₃]^? complexes are present in the solution. However, in the presence of water, water interacts preferentially with the zinc ions, leading to aqueous zinc species. The solvation of zinc ions in 1‐butyl‐1‐methylpyrrolidinium trifluoromethylsulfonate ([Py_1,4]TfO) was also investigated. In [Py_1,4]TfO, there are, on average, 4.5 TfO^? anions coordinating each zinc ion, corresponding to the weak interaction between [Py_1,4]⁺ cations and TfO^? anions. The species present in [Py_1,4]TfO are likely a mixture of [Zn(TfO)₄]^2? and [Zn(TfO)₅]^3?.     

Synthesis of carbamates from carbon dioxide promoted by organostannanes and alkoxysilanes

A cooperative methoxy transfer between orthosilicate esters and organotin oxides was developed for the synthesis of various N ‐alkyl and N ‐aryl carbamates from carbon dioxide in up to 97% isolated yield. The reaction is highly selective and N ‐alkylated amines are not observed. Density functional theory calculations of the reaction were performed and, together with NMR observations, a plausible mechanism featuring the catalytic regeneration of dialkyltin dialkoxide is proposed.     

Synthesis of 3,4-Dihydrophthalazin-1(2H)-one by Zinc Reduction of Phthalazin-1(2H)-one

3,4-Dihydrophthalazin-1(2H)-one (II) was first prepared by H.Sund ¹⁾, by electrochemical reduction of phthalazin-1(2H)-one (I) (phthalazone). In the recent years we have described new syntheses of II, through easily hydrolyzable mono- or diacetyl- derivatives, namely condensation of 2-bromomethylbenzoylchloride with N,N'-diacetylhydrazine ²⁾ catalytic reduction of I in acetic acid ²⁾ or of 2-acetylphthalazone in acetic anhydride ³⁾ The reduction of I with zinc is known to proceed with ring contraction and formation of N-aminophthalimidine (III)⁴⁾ (zinc and sodium hydroxide at about 100[ddot]C) or of phthalimidine (IV) ⁵⁾ (zinc and hydrochloric acid under unspecified conditions).

Having observed that II is transformed into N-aminophthalimidine when heated with hydrazine hydrate ⁶⁾ or sodium hydroxide ²⁾, the zinc reduction of I was reinvestigated with the aim to find out in which cases the intermediate formation of II can be dem-onstratedo     

Experimental and Theoretical Study on New Zn(II) Halide Complexes of 3,5-Diazaindole

3,5-Diazaindole — zinc(II) halide complexes (halogen: Cl, Br, I) are synthesized for the first time. Experimental mid-IR spectra of the compounds were recorded in the range 4000–550 cm^–1, and far-IR spectrum of the zinc(II) chloride complex is recorded in range 700–40 cm^–1. The structural features of the zinc(II) halide complexes of 3,5-diazaindole (ICPY) are studied by quantum chemical methods. The optimized geometry and vibrational frequencies of the ICPY — zinc(II) halide complexes are calculated using the B3LYP/DFT method with the LANL2DZ basis set in the ground state. Vibrational assignments of the most important bands are made with the help of the vibrational energy distribution analysis. The frontier molecular orbital energies, NBO charges, and dipole moments are presented. ¹H and ¹³C NMR spectra of the zinc(II) chloride complex is also given.     

Syntheses,crystal structures,and some spectroscopic properties of zinc(II) complexes with N2O2 ligands derived from m-phenylenediamine and m-aminobenzylamine

The reaction of bis(salicylidene)-m-phenylenediamine with zinc(II) ion affords a 2?:?2 dinuclear zinc(II) complex formulated as [Zn₂(L¹)₂]. A similar 2?:?2 dinuclear zinc(II) complex, [Zn₂(L²)₂], can be obtained by reaction of bis(salicylidene)-m-aminobenzylamine with zinc(II) ion. These two dinuclear complexes slightly differ in their crystal structures, especially coordination environments around the zinc(II) centers, depending on the dissimilar flexibilities of the two ligands. The differences between the two complexes are reflected in their diffuse reflectance and photoluminescence behaviors.     

Synthetic and Structural Studies of Ethyl Zinc β-Amidoenoates and β-Ketoiminates

A set of heteroleptic ethyl zinc β-amidoenoates (1, 2) and β-ketoiminates (3) of the form [LZnEt]₂ with varying steric bulk have been synthesised via the reaction of diethylzinc with β-aminoenoate ligands HL¹ and HL² and β-ketoimine HL³. These complexes have been characterised via ¹H and ¹³C NMR, mass spectrometry and single-crystal X-ray diffraction, which unambiguously determined all three structures as dimeric species in the solid state. We observe the unusual dimerisation of 1 and 2 through coordination of the central zinc atom to the methine carbon of the second monomer, which gives these complexes high reactivity. The thermal properties of complex 3 are explored via thermal gravimetric analysis (TGA), to investigate their potential as single-source precursors to zinc oxide, which shows that 3 has a significantly lower decomposition temperature as compared to its bis-ligated counterpart [Zn(L³)₂], which gives 3 promise as a single-source precursor to zinc oxide.     

Reversible N-Heterocyclic Carbene-Induced α-H Abstraction in Tungsten(VI) Imido Dialkyl Dialkoxide Complexes

The first reversible N-heterocyclic carbene (NHC) induced α-H abstraction in tungsten(VI) imido-dialkyl dialkoxide complexes is reported. Treatment of W(NAr)(CH₂Ph)₂(OtBu)₂ (Ar=2,6-dichlorophenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl) with different NHCs leads to the formation of complexes of the type W(NAr)(CHPh)(NHC)(CH₂Ph)(OtBu) in excellent isolated yields of up to 96 %. The highly unusual release of the tert-butoxide ligand as tBuOH in the course of the reaction was observed. The formed alkylidene complexes and tBuOH are in an equilibrium with the NHC and the dialkyl complexes. Reaction kinetics were monitored by ¹H NMR spectroscopy. A correlation between the steric and electronic properties of the NHC and the reaction rates was observed. Kinetics of a deuterium-labeled complex in comparison to its non-deuterated counterpart revealed the presence of a strong primary kinetic isotope effect (KIE) of 4.2, indicating that α-H abstraction is the rate-determining step (RDS) of the reaction.     

Determination of Zn(II) in natural waters by ICP-OES with on-line preconcentration using a simple solid phase extraction system

An on-line zinc preconcentration and determination system implemented with inductively coupled plasma optical emission spectrometry (ICP-OES) was developed. The zinc was precipitated and retained on a minicolumn filled with ethyl vinyl acetate (EVA) at pH 9.0, without using any complexing reagent. The zinc ions were eluted from the minicolumn with 10% (v/v) hydrochloric acid. Experimental conditions including pH and sample loading and eluting variables were evaluated and established.An enrichment factor (EF) of 44 was obtained for Zn²⁺ with a preconcentration time of 120 s. Under the optimal conditions, the value of the limit of detection (3σ) for the preconcentration of 10 mL of sample was 0.08 μg L^{− 1}. The sampling frequency was about 24 h^{− 1}. The precision for six replicate determinations (repeatability conditions) at 50 μg L^{− 1} Zn level was 3.94% relative deviation standard (RSD), calculated from the peak heights obtained. The methodology was successfully applied to the determination of zinc in tap water samples and in a certified VKI reference material QC Metal LL1 DHI (Water & Environment) Denmark.     

Thermal expansion of the group IIb liquid metals zinc,cadmium and mercury

The volumetric thermal expansions of the group IIb liquid metals zinc, cadmium and mercury were measured using the γ densitometry technique. The data for zinc and cadmium were obtained approximately 200 K above the melting point. Measurements for mercury were made up to 140 K above ambient temperature. The study was conducted to investigate the reported low volumetric thermal expansion of the group IIb liquid metals relative to a large number of other liquid phase elements. The volumetric thermal expansion coefficients in the melt were determined to be 1.41 × 10⁻⁴ K⁻¹ (± 1.5%) for zinc, 1.43 × 10⁻⁴ K⁻¹ (±0.6%) for cadmium and 1.79 × 10⁻⁴ K⁻¹ (± 0.3%) for mercury. These results are in agreement with recent measurements performed using other techniques.