Polymerization of trimethylsilylacetylene by WCl6-based catalysts

The polymerization of trimethylsilylacetylene was investigated by using W and Mo catalysts. Mixtures of WCl₆ with appropriate organometallic cocatalysts such as n-Bu₄Sn and Et₃SiH at 1:1 molar ratio provided poly(trimethylsilylacetylene) in high yields. On the other hand, MoCI₅ gave mainly methanol-soluble oligomers even in the presence of these cocatalysts. The polymer formed was a partly insoluble yellow powder, and the molecular weight of the soluble fraction was about 7000. The IR, ¹H-NMR, and ¹³C-NMR spectra supported the polymer structure, (CH = CSiMe₃)_n. Protodesilylation of poly(trimethylsilylacetylene) afforded a new polymer containing both acetylene and trimethylsilylacetylene units.     

Analysis of kinetic rate constants in [18F]fluorodeoxyglucose model using a least square fitting package SALS (statistical analysis with least squares)

The analysis of kinetic rate constants in the compartment model for [18F]fluorodeoxyglucose (FDG) was undertaken. Four kinetic rate constants were determined with a least square fitting package SALS (Statistical Analysis with Least Squares), using the measured data of 18F activity as a function of time. SALS calculations were found to be easy and quick with high precision. The rate constants and the curves fitted by the k3 and the k4 models were compared in situations with various degree of cerebral glucose metabolism during positron emission tomography (PET) studies. The k4 model in the determination of cerebral metabolic rate for glucose (CMRglu) was much superior than the k3 model in any given situation as it always underestimates the metabolic rate. However, the k3 model produces less variation when the cerebral radioactivity curve shows steady rising pattern.     

Effects of ultraviolet irradiation on substituted polyacetylenes

Effects of UV irradiation on various substituted polyacetylenes were examined. Upon irradiation in air, main-chain scission and crosslinking occurred with a wide range of probabilities dependent on the nature of substituents. For example, poly(2-alkyne)s rapidly degraded to low molecular weights, whereas polymers from aromatic monosubstituted acetylenes [e.g., poly(o-CF₃-phenylacetylene)] were quite stable. Several other polyacetylenes [e.g., poly(1-Me₃Si-1-propyne)] showed intermediate degradability. Polymer degradation was minimal in vaccum. The polymers irradiated in air contained C?O and O? H groups, and dissolved in polar solvents which are nonsolvents for the initial polymers. These results indicate that oxidation causes degradation. Only poly(1-chloro-1-alkyne)s of the polyacetylenes studied, formed gels upon UV irradiation. The amount of the gel was larger, when the polymer was irradiated in vacuum than in air. Further, the longer the alkyl pendant in the polymer, the higher the gel fraction. Differences between photo-and thermal degradations are discussed.     

Electrochemistry of chalcogenoglycosides. Rational design of iterative glycosylation based on reactivity control of glycosyl donors and acceptors by oxidation potentials

Electrochemical properties of various para-substituted phenylthio-, phenylseleno-, and phenyltelluroglucopyranosides bearing acetyl, benzoyl, and benzyl protecting groups have been investigated to estimate the reactivity of chalcogenoglycosides toward electrochemical glycosylations. The oxidation potential of the chalcogenoglycosides shows good correlation with the ionization potential of chalcogen atoms, and decreases in the order thio-, seleno-, and telluroglycosides. It is also affected by the para-substituents, and the substitution effect correlates very well with the HOMO energy of para-substituted benzenechalcogenol and with the Hammett sigma p + value. Electrochemical glycosylation of telluroglycosides has been examined, and it was found that the use of an undivided cell is more effective than the use of a divided cell. Selective activation of the chalcogenoglycosides in bulk electrolysis based on their oxidation potentials has been examined, and the relative reactivity of the telluroglycosides can be estimated from their oxidation potentials. However, the relative reactivity of selenoglycosides in the preparative glycosylation was rather insensitive to the oxidation potential values.     

Selective reduction of ketoesters to hydroxyesters with the use of lithium aluminum hydride in the presence of silica gel

Lithium aluminum hydride, in the presence of a small amount of silica gel, has been found to be a versatile and highly selective reagent for reduction of various ketoesters to the corresponding hydroxyesters in fair yields.     

Transesterification kinetics of phenyl salicylate

The degradation of phenyl salicylate in alkaline aqueous ethanol is shown to proceed via competing transesterification and hydrolysis processes. The transesterified product, ethyl salicylate, also undergoes hydrolysis, but at a slower rate and a kinetic model is presented which allows the simultaneous determination of all three rate constants. These results are contrasted with those of an earlier literature study and show the necessity for specific assay systems in kinetic analysis.     

A Rare Low‐Spin CoIV Bis(β‐silyldiamide) with High Thermal Stability: Steric Enforcement of a Doublet Configuration

Attempted preparation of a chelated Co^II β‐silylamide resulted in the unprecedented disproportionation to Co⁰ and a spirocyclic cobalt(IV) bis(β‐silyldiamide): [Co[(N^tBu)₂SiMe₂]₂] ( 1 ). Compound 1 exhibited a room‐temperature magnetic moment of 1.8 B.M. and a solid‐state axial EPR spectrum diagnostic of a rare S= configuration for tetrahedral Co^IV. Ab initio semicanonical coupled‐cluster calculations (DLPNO‐CCSD(T)) revealed the doublet state was clearly preferred (?27 kcal mol^?1) over higher spin configurations only for the bulky tert‐butyl‐substituted analogue. Unlike other Co^IV complexes, 1 had remarkable thermal stability, and was demonstrated to form a stable self‐limiting monolayer in preliminary atomic layer deposition (ALD) surface saturation experiments. The ease of synthesis and high stability make 1 an attractive starting point to investigate otherwise inaccessible Co^IV intermediates and for synthesizing new materials.     

Polymerization of silicon-containing acetylenes. 5. Polymerization of 1-silyl-1-propynes by TaCl5-based catalysts

Polymerization of homologues of 1-(trimethylsilyl)-1-propyne [CH₃C?CSi(CH₃)₃] was studied. CH₃C?CSi(CH₃)₂(n-C₆H₁₃) ( I ) polymerized with 1 : 1 mixtures of TaCl₅ and organometallic cocatalysts (e.g., Ph₄Sn and Ph₃Bi) to produce in good yields a polymer having a weight-average molecular weight (M _w) over 1 × 10⁶. CH₃C?CSi(CH₃)₂ Ph ( II ) and CH₃C?CSi(C₂H₅)₃ ( III ) formed polymers having M _w's of ～ 5 × 10⁵ in moderate yields in the presence of TaCl₅-based catalysts. In contrast, none of CH₃C?CSi(CH₃)₂(i-C₃H₇), CH₃C? CSi(CH₃)₂(t,-C₄H₉), C₂H₅C?CSi(CH₃)₃, and n,-C₄H₉C?CSi(CH₃)₃ polymerized, which is attributed to the steric effect of the monomers. Some other 1-silyl-1-propynes also failed to polymerize. The three new polymers formed from ( I )–( III ) had the structure \documentclass{article}\pagestyle{empty}\begin{document}$\rlap{--} [{\rm CCH}_{\rm 3} \hbox{=\hskip-2pt=} {\rm C(SiRR'R''}\rlap{--} ]_n$\end{document} according to IR and ¹³C-NMR spectra. They were white solids, soluble in low-polarity solvents (e.g., toluene and chloroform) and stable enough in air at room temperature.     

Capillary isotachophoretic determinations of metal ions by use of complexation equilibria in acetone-water medium

The determination of metal ions by capillary isotachophoresis and the complexation equilibria between metal ions and polyaminopolycarboxylic acids has been investigated. A seven-component mixture of metal ions can be separated in 45% v/v acetone-water medium when EDTA or DCTA is used as the terminating ion. Linear calibration graphs are obtained for a standard mixture of Mn(+), Cu(2+), Zn(2+), Cd(2+), Pb(2+) and Fe(3+) in the range 0.5-5.0 nmole, with relative standard deviations of 1.0% or better. The effective mobilities of the Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes increase in parallel with the stability constants, except for the Cu(II) complexes. It is concluded that the abnormal behaviour of the Cu(II) complexes may be attributed to a difference in steric configuration.