Influence of structure on electrochemical reactivity of anions of 1,1-dinitroalkanes during their oxidation

Conclusions The electrochemical reactivity of 1,1-dinitroalkane salts during anodic oxidation is determined mainly by the inductive and -effects of the substituents.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2690–2693, December, 1987.     

The influence of the molecular structure of polymers on their reactivity in polycondensation

The influence of the conditions of synthesis, the chain length and the chemical structure of macromolecules on their reactivity is examined. The main emphasis is placed on the connection between polymer molecular structure and macromolecular effects in polycondensation. The far order effect is presented as the principal chemical factor determining the reactivity of macromolecules in solution polycondensation reactions.     

Synthesis and reactivity of dimethyl platinum(IV) hydrides in water

New hydrophilic ligands of the di(2-pyridyl)methanesulfonate family, L = dpms and Me-dpms, enable the synthesis of methyl platinum(IV) hydrides, LPtMe2H, the study of very fast CH reductive coupling, and reductive elimination of these complexes in water. In dichloromethane solutions, 13CH4 reacts with (Me-dpms)PtMe2H to produce isotopomeric complexes.     

Intramolecularly coordinated organotin(IV) sulphides and their reactivity to iodine

Organotin(IV) sulphides (LSnPhS)₂ (3) and (LSnPh₂)₂S (4) containing O,C,O chelating ligand (L = 2,6-(t BuOCH₂)₂C₆H₃⁻) were prepared by the reaction of parent organotin chlorides LSnPhCl₂ (1) and LSnPh₂Cl (2) with Na₂S · 9H₂O in toluene/water. Both sulphides were characterized by the help of elemental analysis, ESI-mass spectrometry, ¹H, ¹³C ¹¹⁹Sn NMR spectroscopy and the molecular structure of 3 was determined by X-ray diffraction techniques. Compounds 3 and 4 react with I₂ to organotin iodides LSnPhI₂ (5) and LSnPh₂I (6), instead of intended iodolysis of phenyl groups. Triorganotin iodide 6 reacts with the additional molecule of I₂ forming an ionic organotin compound [ LSnPh₂]⁺ I₃⁻ (7), which is unstable in solution and decomposes to Ph₂SnI₂ and 2,6-(tBuOCH₂)₂C₆H₃I (8).     

Preparation and reactivity of a monomeric octahedral platinum(IV) amido complex

Synthesis and isolation of the monomeric octahedral platinum(IV) amido complex (NCN)PtMe2NHPh have been accomplished upon deprotonation of the amine complex [(NCN)PtMe2(NH2Ph)][OTf]. The preliminary reactivity of the amido ligand has been explored.     

Selenium(IV) fluoride and oxofluoride anions

The [((C₆H₅)₃P)₂N]⁺, [(C₆H₅)₄P]⁺ and [N(CH₃)₄]⁺ salts of SeF₅⁻, SeF₆²⁻ and SeOF₃⁻ and CsSeO₂F were prepared and characterized. Crystal structures were obtained for [((C₆H₅)₃P)₂N][SeF₅] and [((C₆H₅)₃P)₂N][SeOF₃] CH₂Cl₂. In contrast to oxygen-bridged dimeric TeOF₃⁻, the SeOF₃⁻ anion in [((C₆H₅)₃P)₂N][SeOF₃] CH₂Cl₂ is monomeric and represents the first experimentally well determined molecular structure of a monomeric trifluoro-chalcogenite anion. Similarly, [((C₆H₅)₃P)₂N][SeF₅] represents the first example of a structure containing a well-isolated undistorted SeF₅⁻ anion. The NMR and the vibrational spectra and their assignments were re-examined and corrected by comparison with high-level theoretical calculations. Whereas the previously published normal coordinate analysis of SeF₅⁻ is correct, that for SeOF₃⁻ needs major revision.     

Extractive separation and photometric determination of neptunium(IV) and plutonium(IV) from their mixtures

A rapid and sensitive method for the photometric determination of trace amounts of neptunium and plutonium from their mixtures is described. Np(IV) is selectively extracted from about 1 M HNO₃ medium with TTA in xylene retaining Pu in the nonextractable trivalent state in the aq. phase with ferrous sulfamate. Plutonium in the aqueous phase is subsequently oxidized with NaNO₂ to the highly extractable tetravalent state and extracted with TTA. Np(IV) as well as Pu(IV) thus extracted are finally estimated in the organic phase itself spectrophotometrically employing xylenol orange as the chromogenic reagent. Their molar absorptivities are in the 5 × 10⁴ range. Beer's law is valid up to 2.4 ppm Np and 3.5 ppm Pu. The color of the solutions is stable for at least 48 hr. The method tolerates large excess of several common contaminants encountered during spent fuel reprocessing. Cerium(IV) and phosphoric acid, however, interfere with the final estimation.     

Adsorption of anions to zirconium(IV) and titanium(IV) chemically immobilized on gel-phase

Adsorption behaviors of 25 anions to zirconium(IV) and titanium(IV) chemically immobilized on a gel-phase were studied by ion chromatography and by batch adsorption experiments. The affinities of Zr(IV) to iminodiacetate as an anchoring group and to anions as a sample are much stronger than those of Ti(IV). On a Zr(IV) column, fourteen anions showed no retention, four anions showed pH-dependent retention in a low pH region, and seven anions were irreversibly adsorbed at pH <7. In the last group, fluoride was adsorbed both by the ligand exchange mechanism and the addition mechanism, while phosphate, arsenate and selenite were only by the ligand exchange mechanism. The structures of the adsorbed species are discussed.     

The synthesis and x-ray structure of (N,N-dimethyldithiocarbamato)(n-butyl)diphenyltin(IV)

(N,N-Dimethyldithiocarbamato)(n-butyl)diphenyltin(IV), n-BuPh₂SnS₂NMe₂, crystallizes in the monoclinic space group P2₁/n with a 9.772(5), b 9.895(4), c 21.418(9) Å, β 95.81(3)⁰, V 2060 ų Z = 4, μ 14.4 cm⁻¹ The structure was determined by the heavy-atom technique from 3103 independent reflections measured at room temperature on an Enraf-Nonius four-circle CAD-4 diffractometer using monochromatized Mo-K radiation and refined to a final R value of 5.8%. The tin atom is essentially four-coordinated with a weak fifth tin-sulphur bond (Sn---S(2) 3.079(1) Å) considerably longer than the other (Sn---S(1) 2.466(1) Å). A comparison with the complex n-BuPhSn(C1)S₂CNEt₂ (Sn---S(1) 2.454(1) Å; Sn---S(2) 2.764(1) Å) suggests that enhanced steric factors are responsible for the preferential monodentate behaviour of the dithiocarbamate ligand in the title complex.     

The x-ray structure of the h5-cyclopentadienyltris(tropolonato)zirconium(IV) 1:1 dichloromethane solvate

X-ray structure analysis has shown that h⁵-cyclopentadienyltris(tropolonato)zirconium(IV) may be regarded as seven-coordinate with a slightly distorted pentagonal bipyramidal geometry; the h⁵-cyclopentadienyl group occupies an axial position.     

Preparation and x-ray crystal structure of racemic bis(ethylfumarate)bis(acetonitrile)cobalt(0)

The preparation and properties of some new tetracoordinated cobalt(0) complexes containing nitrile and fumaric ester ligands are described. One of them, Co(C₂H₅OOCCHCHCOOC₂H₅)₂(CH₃CN)₂, (la), reacts with 1,10-phenanthroline to give new pentacoordinated and hexacoordinated cobalt(0) complexes.The structure of Ia has been determined from X-ray diffractometer data. The structure was solved by Patterson and Fourier methods and refined by least square techniques to R  0.060 for 2215 independent reflections. Crystals are triclinic, space group P$\text{1}$, with Z  2 in a unit cell of dimensions: a 14.794(18), b 9.448(11), c 10.125(12) Å, α 108.55(9), β 111.42(11), γ 84.95(18)°. The metal is linked to the four carbon atoms of the CHCH groups of the ethyl fumarate residues and to the nitrogen atoms of the two acetonitrile ligands. The coordination of the four ligands around the cobalt atom corresponds to a distorted trigonal pyramid. The four asymmetric carbon atoms of a molecule have the same absolute configuration. RRRR and SSSS molecules are present in the unit cell.     

Peptide synthesis in water IV. Preparation of N-ethanesulfonylethoxycarbonyl (Esc) amino acids and their application to solid phase peptide synthesis

A new N-protecting group, ethanesulfonylethoxycarbonyl (Esc), was designed to perform peptide synthesis in both aqueous and organic solvents. Esc-amino acids were prepared by the reaction of Esc-Cl and amino acids. Although Esc-Cl was a highly reactive reagent, it was not stable and decomposed during the purification procedure. A more stable reagent, ethanesulfonylethyl-4-nitrophenyl carbonate (Esc-ONp), was designed for preparation of Esc-amino acids. Esc-ONp was a stable reagent and could be purified by silica gel column chromatography or recrystallization. Esc-amino acids were prepared by the reaction of Esc-ONp and amino acids in good yield. To evaluate Esc-amino acids, Leu-enkephalin amide was synthesized using Esc-amino acids by the solid phase method in water. Removal of the Esc group was performed with 0.025 mol/l NaOH in 50% aqueous ethanol. Leu-enkephalin amide was successfully synthesized on a poly(ethylene glycol)-grafted polystyrene resin. Esc-amino acids have moderate solubility in organic solvents (such as dimethylformamide and acetonitrile). Leu-enkephalin amide was synthesized using Esc-amino acids by the solid phase method in dimethylformamide. Removal of the Esc group was performed with 0.05 mol/l tetrabutylammonium fluoride in dimethylformamide. Synthesis of Leu-enkephalin amide using Esc-amino acids in dimethylformamide was also successful. The yields of synthesis of Leu-enkephalin amide in water and dimethylformamide were 71% and 67%, respectively.     

The influence of anions and kink structure on the enantioselective electro-oxidation of glucose

The electro-oxidation of glucose in sulfuric acid using well-defined chiral platinum single crystal electrodes has been demonstrated previously to be an enantioselective reaction with the degree of enantioselectivity being dependent on the surface density of kink sites. The chirality of the surface originates from the microstructure of the kink site whereby the sequence of the three fundamental adsorption sites [111], [100] and [110] constituting the kink may be viewed from the electrolyte phase either in a clockwise (R-enantiomer) or anti-clockwise (S-enantiomer) fashion. In the present study, this work is extended to examine the role of both kink structure and specifically adsorbed anions on the mechanism of chiral discrimination. Kinked surfaces based on [111] terraces (Pt[976],Pt[643] and Pt[531]),[100] terraces (Pt[721]) and [110] terraces (Pt[11,7,1] and Pt[841]) have been investigated and both the magnitude and potential dependence of the enantioselective electro-oxidation of glucose characterised. Additionally, the changes engendered by interchanging the character of the two steps whose confluence form the kink whilst maintaining the symmetry of the terrace has also been examined via a comparison of Pt[643] and Pt[431]. Low energy electron diffraction (LEED) was used to confirm that all surfaces when clean and thermally annealed were in their (1 x 1) state. Cyclic voltammetry (CV) confirmed this finding for flame-annealed electrodes after cooling in hydrogen. Three general points emerge from the electro-oxidation studies: (i) The highest degree of enantioselectivity is exhibited by kink sites adjacent to [111] and [110] terraces in sulfuric acid. (ii) The adsorption of specifically adsorbed anions like bisulfate/sulfate influences strongly the chiral discriminatory behaviour of all surfaces. (iii) No electro-oxidation takes place at [110] sites, as evidenced by complete overlap of the [110] step hydrogen underpotential deposition (UPD) charge in glucose and glucose-free solutions. Nonetheless it is deduced that [110] sites must play some part in the initial orienting of the glucose molecule prior to reaction. Ideas based on these findings are developed in order to rationalise in particular the influence of anion adsorption on the initial enantioselective interaction of the glucose molecule with the chiral surface.     

The x-ray structure determination and semiempirical PM3 calculations of 2,4,4,6,6-pentachloro-2-(piperidyl)cyclotri(phosphazene)

The structure of 2,4,4,6,6-pentachloro-2-(piperidyl)-cyclotri(phosphazene) ( 1 ) was determined by single-crystal X-ray diffraction analysis. Compound 1 crystallizes in the orthorhombic space group P_bea with Z = 8 and unit cell dimensions a = 8.316(2), b = 17.261(3), and c = 22.007(4) Å. The experimentally obtained structural parameters for compound 1 compare well with those calculated at the semiempirical PM3 level of theory. These results give credence to the PM3-calculated structure of 2,4,4,6,6-pentaazido-2-(piperidyl)cyclotri(phosphazene) ( 2 ) for which presently there are no experimental data available.

1 Non-SI units employed: 1 kcal≈︁4.184 kJ, 1 Å = 10⁻¹⁰ m since these units are still used in computational chemistry, we employed them throughout this article.

© 1997 John Wiley & Sons, Inc. Heteroatom Chem 8: 283–286, 1997.     

The synthesis and reactivity of a molybdenum (IV) stretched-dihydrogen complex

Reaction of [Mo(NPh)(PMe3)3(o-(Me3SiN)2C6H4)] (1) with molecular hydrogen (ca. 1 atm) at -10 degrees C in toluene-d8 results in the formation of dihydrogen complex [Mo(NPh)(PMe3)2(H2)(o-(Me3SiN)2C6H4)] (2) by 1H and 31P NMR spectroscopy. In solution at -50 degrees C 1 and 2 are present in a 1:3 ratio, respectively. The nature of dihydrogen ligand bonding in 2 was probed by T1 analysis and analysis of the JH-D coupling constant in the deuterium hydride isotopomer of 2 giving H-H distances of 1.18 A and 1.17 A, respectively. When allowed to warm to 30 degrees C, 2 reacts affording [Mo(NPh)(PMe3)3(o-(Me3SiN)(NH)C6H4)] (3) over a 1 h period. The X-ray structures of 1 and 3 are reported.     

Nuclear magnetic resonance and x-ray determination of the structure of poly(vinylidene fluoride)

In this study, wide-line NMR and x-ray diffraction have been used in conjunction to study the crystal structure of poly(vinylidene fluoride). Drawn poly(vinylidene fluoride) film was found to contain two crystal phases, the relative amounts of each depending on the draw temperature. Drawing at 50°C. yields a single phase, designated as phase I, while drawing at temperatures between 120 and 160°C. yields a mixture of phase I and a second phase (phase II). The fraction of phase II increases with increasing draw temperature, but this phase was never obtained without some phase I. A tentative orthorhombic unit cell is proposed for phase II. The structure of phase I has been determined from x-ray data. The unit cell is orthorhombic, space group Cm2m, having lattice constants a = 8.47, b = 4.90, and c (chain axis) = 2.56 A. There are two polymer chains in this unit cell. The conformation of the polymer chains is planar zigzag. The details of this structure have been confirmed by experimentally determining at ?196°C. the change in the NMR second moment with the angle between the magnetic field and the draw direction of phase I (drawn at 50°C.), and by comparing these results with a theoretical calculation of the second moments, based on the atomic positions obtained from the proposed structure.     

Preparation and x-ray structure of 1,4,2,3,5,6-Dithiatetrazine

Reaction of sulfur dichloride with sym-EtO₂CNHNHCO₂Et 1 gives the title ring system which has been characterised by microanalyses, nmr, and X-Ray crystallography. The X-ray structure of S₂[N(CO₂Et)]₄ 2 reveals that the S₂N₄ ring adopts a chair conformation with all four ester groups in pseudo-axial positions. Bond lengths and angles are compared with 1 and S₄(NR)₂.