Selectivities in 1,2,3-triazolide displacements of halides and additions to alkynes

4,5-Dicarbomethoxy-1,2,3-triazolide or 4-phenyl-1,2,3-triazolide displace chloride from ethyl chloroacetate or β-chloropropionate to give both 1-N and 2-N alkylated products. Our highest 2-N to 1-N selectivity was ca 5/1 and was found with the base triethylamine in DMF. The same triazolides and others add to alkynes, e.g. ethyl propiolate, methyl acetylenedicarboxylate, phenylpropiolaldehyde, ethyl phenylpropiolate, etc, to give Michael adducts at the 2-N position exclusively. Here the usual preference holds, i.e., the anti adduct is favored, but anti to syn isomerization usually sets in. On the basis of the available data for nucleophilic substitutions and additions, a limited directioselectivity pattern emerges for H-1,2,3-triazoles (T) and their anions (T^?): neutral T almost invariably leads with 1-N; T^t-- usually adds to unsaturates at 2-N; unsubstituted, 4-substituted and 4,5-disubstituted T^? attack organic halides at both 1-N and 2-N. Compared to phenyl, 2-triazolyl exerts a greater deshielding effect on proton chemical shifts; these and other patterns in the PMR spectra of the Michael adducts are discussed. CNDO calculations indicate that the 1-H is more stable than the 2-H-1,2,3-triazole and that in both neutral triazole and in triazolide, the 1-nitrogen position should lead nucleophilic attacks-this directioselectivity prediction is only partly (and probably fortuitously) correct.     

On the structure of Pd,Pt and Rh complexes with 1,5-hexadiene

A number of halogen complexes of Pd, Pt and Rh with 1,5-hexadiene have been synthesized;three of them, C₆H₁₀PdBr₂, C₆H₁₀PtBr₂ and (C₆H₁₀RhCl)₂, for the first time. An intermediate while preparing C₆H₁₀PdCl₂ was the polynuclear polymeric moiety [C₆H₁₀(PdCl₂)₄]_n· IR, Raman and ESCA spectroscopy show that the diallylic ligand in all the complexes has the cis-configuration and that the strength of the metaldiallyl bond increases in the series Pd < Pt < Rh.     

Preparation and magnetic properties of manganite

A new hydrothermal synthesis of manganite is described, and the magnetic and electron paramagnetic resonance (EPR) behavior of the product is reported. The magnetic susceptibility is nearly independent of temperature above 90°K and increases dramatically on cooling to 30°K. The EPR lineshape, linewidth, and g-factor at 296°K are Lorentzian (in the central region), 280 ± 10 G, and 1.997 ± 0.006, respectively. The EPR spectrum is interpreted in terms of nearly one-dimensional interactions between identical Mn moments. The results of this study support the view that all Mn ions are trivalent and that the magnetic interactions between these ions are nearly one dimensional.     

Spectral and electrochemical studies on oxoisothiocyanatobis(pyrrolidinyldithiocarbamato)molybdenum(V)

The complex, oxoisothiocyanatobis(pyrrolidinyldithiocarbamato)molybdenum(V), MoO(NCS) (pyrroldtc)₂ was prepared. The IR spectra of the complex suggest that the thiocyanate group is attached through nitrogen and the presence of MoO³⁺ moiety. The voltammograms of the complex in acetonitrile exhibited a pronounced cathodic wave at ?0.23 V vs S.C.E. which was attributed to Mo(V)/Mo(IV) couple. The magnetic, epr and electrochemical studies indicate that the compound is mononuclear and molybdenum is in +5 oxidation state.     

σ→π*, A reassignment of the long wavelength uv transition in acyl-silanes and -germanes by photoelectron spectroscopy

The first vertical ionization potentials, as measured by photoelectron spectroscopy, of Me₃SiC(O)Me and Me₃GeC(O)Me are found to be 8.6 and 8.5 eV respectively. On the basis of the broad photoelectron band width and modified CNDO/2 calculations, strong mixing between the Iocalized oxygen Ione pair and metalcarbon bond is suggested as the major origin of the shift of the 280 nm UV transition of aliphatic ketones to longer wavelengths in R₃MC(O)R (370 nm) and (R₃M)₂CO (500 nm),M is Si or Ge.     

Preparation and properties of some stable arsonium ylides

Stable crystalline arsonium ylides have been prepared by thermal decomposition of diazo compounds in the presence of triphenylarsine, and by condensation reactions of reactive methylene compounds with triphenylarsine oxide. The spectra of these ylides, and their reactions with benzaldehydes are discussed. Like other stabilised arsonium ylides they give alkenes rather than epoxides in Wittig reactions. They are generally more polar than their phosphonium analogues and also are more reactive in the Wittig reaction. With diphenylcyclopropenone some more reactive arsonium ylides form α-pyrones.     

Spectroscopic and scattering investigation of isopoly-molybdate and tungstate solutions

Detailed spectroscopic and scattering investigations of isopoly-molybdate and -tungstate solutions as a function of concentration and pH were made. From scattering results the apparent molecular weights were determined as a function of time and concentration. We find that the result agree with the aggregation scheme of simple → hepta → octa → [Mo₃₆O₁₁₂]^?8 → protonated polymeric species, for molybdate solutions. Tungstate solutions aggregate according to simple → Y-polytungstate → paratungstate-A → paratungstate-B → Ψ-metatungstate. The molybdate solutions exhibited very rapid equilibration, but the tungstate solutions required several days to reach equilibrium. From the discrete changes in the Raman spectra of both systems we find that the formation of isopoly anions is not a continuous process and that only certain species are present in solution. Our results do not rule out the formation of significant quantities of the octamolybdate anion as suggested by previous investigators.     

Thermodynamics of solid-state connected ion-sensitive membrane electrodes: The silver-silver chloride system: Part I. Standard potential EM0 at 25, 50, and 75°C

Standard potentials E_M⁰ at 25, 50 and 75°C of all-solid-state silver-silver chloride ring membrane electrodes (Schott) with pressed-in silver foil have been measured with respect to the Pt, H₂ electrode by means of a cell without transference (see also [1]) applied earlier by Bates and Bower who measured standard potentials E⁰ of corresponding electrodes of the 2nd kind. The data evaluated by the extended Debye-Hückel theory can directly be compared with the reported 2nd kind electrode data. Identical thermodynamic behavior of both electrode types is observed; small differences (<1.5 mV) of standard potentials and their temperature dependence are discussed on the basis of different states of electrode materials orignating from different electrode preparation and are applied to calculate thermodynamic data of membrane electrodes referred to those of electrodes of the 2nd kind. The results and contradictory literature data are discussed. A brief characterization of membrane and 2nd kind electrodes is given.     

Preparation and properties of metallacyclobutanes of nickel and palladium

Bis(phosphine)-3,3-dimethylnickela- and palladacyclobutanes have been prepared by intramolecular C-H insertion reaction of the corresponding dineopentyl metal complexes. Nickelacyclobutane complexes decompose when heated thereby undergoing competitive carbon-carbon bond cleavage to give isobutene and ethylene, with reductive elimination affording 1,1-dimethylcyclopropane and skeletal isomeri-zation of the metallacyclic ring yielding 3-methyl-1-butene, whereas the palladium analog gave no significant amounts of CC bond cleavage products.Added phos-phine was seen to have an effect on CC bond scission of nickelacyclobutane complexes. Nickelacyclobutane complexes in solution are thought to be in equilibrium with olefin-coordinated nickel-carbene complex on the basis of available experimental evidence from hydrogenolysis, carbene-trap reactions with olefins and reaction with carbon monoxide     

Solvation of alkyllithium compounds. Steric effects on heats of interaction of bases with trimethylsilylmethyllithium versus n-butyllithium

Skeletal rearrangement in solvomercuration of olefins has been found to be dependent on the polarity of the HgX bond.     

Electrophilic radiofluorination of aryltrimethylsilanes as a general route to 18F-labeled aryl fluorides

The reactions of a variety of aryltrimethylsilanes with elemental fluorine and acetyl hypofluorite have been studied with the aim of developing a general method for labeling aromatic compounds with fluorine-18. Extensive ¹⁸F incorporation into the aromatic ring of the selected aryltrimethylsilanes was invariably observed, leading to the ipso (¹⁸F-for-Si) electrophilic substitution products together with variable yields of other (¹⁸F-for-H) electrophilic substitution products. The relative extent of the ¹⁸F substitution processes [(C-Si/C-H)subst.] is found to depend largely upon the substituent group on the aromatic ring of the substrate, the leaving moiety, and the radiofluorination procedure used. The utility of aryltrimethylsilyl derivatives as precursors for the rapid synthesis of high specific activity of ¹⁸F-labeled radiopharmaceuticals is discussed.     

(Cyclopentadienyl)(1-methylallyl)(butadiene)titanium

(Cyclopentadienyl)(1-methylallyl)(butadiene)titanium, C₁₃H₁₈Ti, has been obtained from the reaction between (C₅H₅)TiCl₃ or (C₅H₅)TiCl₂ and 1-methylallylmagnesium bromide in ether. The brown compound is diamagnetic and thermally stable, but very sensitive to oxygen. The nature of the new compound has been elucidated from its reaction with bromine and by IR, ¹H and ¹³C NMR, and mass spectral analysis.     

On the crystal structures of the fluorite-related intermediate rare-earth oxides

The binary oxides of the rare-earth elements are, except for the A- and B-type sesquioxides, members of a fluorite-related homologous series R_nO_2n?2 (n = 4, 6, 7, 9, 10, 11, 12, ∞ are well established and a related phase with $\text{n = 10}\text{1}\text{3}$ has been reported). In this paper an electron optical study of members of the series is discussed which reveals the unit cell dimensions and possible space groups of the intermediate phases as well as the transformation matrices in terms of the fluorite substructure. This information reveals the structural relationships among the members of the series as well as the highest common structural feature involved. Structures are proposed for members of this series consistent with the new results obtained and with the data already in existence.     

A kinetic study of the oxidation of ζ phase praseodymium oxide: 109Pr9O16 + 19O2 → Pr10O18

Kinetic and thermodynamic studies of the oxidation of ζ (n = 9 in Pr_nO_2n?2) to epsilon (n = 10) phase have been carried out using a thermogravimetric technique. The experiments covered a temperature range of 464 to 503°C and oxygen pressure varied from 0.01 to 50 Torr. The existence of a reproducible hysteresis loop which depends on the temperature and pressure is shown. Measurements of the oxidation rate under isothermal conditions were fitted to different rate equations and have been found to be well represented by the equation f = 1 ? (1 ? kt)³. This fact indicated that the process of oxidation was predominantly controlled by the chemical reaction at the interface. The activation energy for the reaction has been calculated to be 15.9 kcal/mole.     

Reaction of benzyne with cyclic olefins—II : Ene addition to some cycloalkenes

Addition of benzyne to 1-methylcyclohexene, (+)-carvomenthene, (+)-limonene, α- and β-pinenes and δ³-carene has been investigated. Structures to the ene products formed are assigned on the basis of spectroscopic evidence. Arguments are advanced in favour of a concerted ene mechanism for the addition of benzyne to these olefins.     

Skipped diynes—VII : Stereospecific thermal isomerization of a tetraethynyldimethylenecyclobutane

1,1-Bis(t-butylethynyl)-3-t-butylchloroallene (1) dimerizes stereospecifically at ca 25° to give Z - 1 - (t - butylchloromethylene) - 2- bis(t - butylethynylmethylene) - 3 - t - butyl - 3 - chloro - 4,4 -bis(t - butylethynyl)cyclob Z-I in the solvent bis(2 - ethoxyethyl) ether. Rate data for 100° are k = 111 × 10^?6 sec^?1, ΔH^≠ = 30·8 ± 1 kcal/mole and ΔS^≠ = 15 ± 3 eu. It is proposed that the dimerization of 1 produces a bisallyl diradical in an orthogonal conformation from which conrotatory paths lead to Z-I or trans-II. The observations on this system are used to construct a useful, if simplistic, approach to rationalize or predict product distributions in reactions such as allene dimerizations, 1, 2 - dimethylenecyclobutane rearrangements, etc, which proceed through the bisallyl diradical. On the graph which connects all of the species (or on the energy surface which contains all of the species) the first products should be those which are one allowed reaction step away from a given diradical. Applications and exceptions to this concept of favored kinetic control are discussed.     

Nucleophilic aromatic substitution of activated cationic groups by 18F-labeled fluoride. A useful route to no-carrier-added (NCA) 18F-labeled aryl fluorides

A method is described for the rapid preparation of no-carrier-added (NCA) ¹⁸F-labeled aryl fluorides by treatment of the corresponding aryltrimethylammonium perchlorates with ¹⁸F-labeled fluoride in DMSO. The basic features of the ¹⁸F-for-⁺NMe₃ displacement process are evaluated as a function of the experimental variables and compared with related substitution routes to NCA ¹⁸F-labeled aryl fluorides. The relative nucleofugicity of the ammonium group in the nucleophilic substitution reactions surpasses that of the best neutral leaving groups, including NO₂ and F itself. In contrast, radiofluoride incorporation into aromatic rings $\text{via}$ other cationic substrates, such as aryldimethylsulfonium perchlorates, is prevented by the fast methyl group transfer from the starting compound to the nucleophiles present. The use of the ammonium function as a leaving group in nucleophilic substitutions by ¹⁸F^? may give access to the rapid preparation of novel NCA ¹⁸F-radiopharmaceuticals by facilitating the synthesis and the purification of their labeled precursors.     

Bis(dialkylmetall)quadratate der elemente aluminium,gallium und indium

The reaction of squaric acid, H₂C₄O₄, with the trialkyl derivatives of aluminium, gallium and indium (R₃M with R = CH₃, C₂H₅) in a $\text{1}\text{2}$ molar ratio leads to bis(dialkylmetal) squarates. The Ga and In compounds dissociate in water forming R₂M⁺ and C₄O₄^2? ions. From these solutions the squarates crystallize as mono- and dihydrates, respectively. The vibrational spectra (IR and Raman) are discussed.