Oxidative versus reductive additions: A 13C NMR study of H2, HX (X = Cl,Br, OR I), and Cl2 additions to some iridium(I) complexes

The ¹³C NMR spectra of a number of iridium complexes and of their adducts with H₂, HX, and Cl₂ (X = Cl, Br, I) are used to estimate the redox character of these additions. Rather than having the oxidative character expected, H₂ addition seems to be reductive. HX and Cl₂ additions are oxidative. Some of these complexes appear to have Lewis acid, rather than the expected Lewis base character.     

Steric Stabilization of Colloids by Poly(dimethylsiloxane) in Carbon Dioxide: Effect of Cosolvents

Steric stabilization and flocculation of colloids with surface-grafted poly(dimethylsiloxane) (PDMS) chains are examined in liquid and supercritical carbon dioxide with and without hexane as a cosolvent. Neither poly(methyl methacrylate) (PMMA) nor silica particles with grafted 10,000 g/mol PDMS could be stabilized in pure CO(2) at pressures up to 345 bar at 25 degrees C and 517 bar at 65 degrees C without stirring. The addition of 15 wt% hexane to CO(2) led to stable dispersions with sedimentation velocities of 0.2 mm/min for 1-2 μm PMMA particles. The critical flocculation pressure of the colloids in the hexane/CO(2) mixture, determined from turbidity versus time measurements, was found to be the same for silica and PMMA particles and was well above the upper critical solution pressure for the PDMS-CO(2) system. The addition of a nonreactive cosolvent, hexane, eliminates flocculation of PMMA particles synthesized through dispersion polymerization in CO(2) with PDMS-based surfactants. Copyright 2000 Academic Press.     

A convenient one-pot synthesis of 1,8-naphthyridones

In this paper, we disclose an efficient one-pot procedure for the preparation of substituted 1,8-naphthyridin-4-one analogues. Previous efforts to effect this type of transformation were complicated by the formation of benzene tricarboxylate. Via the use of excess base, the impurity formation was completely inhibited. This allowed for the clean preparation of the desired intermediate and subsequent formation of naphthyridone analogues in a single flask, which could then be crystallized directly from the reaction mixture in good yield and high purity.     

Pentakis(methoxycarbonyl)cyclopentadiene,a strong organic acid: Crystal and molecular structures of HC5(CO)2Me)5 and Li[C5(CO2Me)5](H2O)

Contrary to some previously depicted structures, the proton in HC₅(CO₂Me)₅ is bonded to two oxygens rather than to carbon; the lithium ion in Li[C₅(CO₂Me)₅] (H₂O) is tetrahedrally coordinated by two carbonyl oxygens from one C₅ anion, one from a second anion, and a water molecule.     

Thianaphthenoyltrifluoroacetone as an analytical reagent: The keto-enol tautomerism of the 2- and 3-isomers of thianaphthenoyltrifluoroacetone

Summary The keto-enol tautomerism of the 2- and 3-isomers of thianaphthenoyltrifluoroacetone has been studied and the results explained by considering the relative negativities of the 2- and 3-position of thianaphthene. The results of the comparison of the keto-enol tautomerism of 3-thianaphthenoyltrifluoroacetone to that of 2-thenoyltrifluoroacetone in 80% benzene-20% ethanol may explain in part the greater sensitivity of the former in trace metal analysis.

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Zusammenfassung Die Keto-Enol-Tautomerie der 2- und 3-Isomeren des Thianaphthenoyltrifluoracetons wurde untersucht und mit der relativen Negativität der 2- und 3-Stellung des Thianaphtens zu erklären versucht. Der Vergleich der Keto-Enol-Tautomerie von II mit der des 2-Thenoyltrifluoracetons in BenzolÄthanol (80+20) könnte eine Erklärung für die größere Sensitivität von II bei der Spurenmetallanalyse bieten.

     

Synthesis of sodium tantalate nanorods by alkalide reduction

NaTaO3 nanorods were synthesized with high (>90%) yield by reduction of TaCl5 with THF solutions of the alkalide K+(15C5)2Na-, followed by product annealing under dynamic vacuum at 250 and 600 degrees C. In addition to the nanorods, the product is comprised of 5-10% approximately 10-nm diameter spheroidal NaTaO3 nanocrystals. The nanorods are generally longer than 500 nm, with some exceeding 1 mum, and 10-100 nm wide, with aspect ratios that vary between 10 and 20:1. Select area electron diffraction patterns of individual nanorods indicate that each nanorod is a single crystal with its axis oriented in the [010] direction.     

Phase behavior and rheological properties of polyelectrolyte inks for direct-write assembly

Three-dimensional (3-D) structures with micron-sized features have been fabricated via the direct-write assembly of polyelectrolyte inks. By mixing oppositely charged species under solution conditions that promote polyelectrolyte exchange reactions, we have created concentrated fluids capable of flowing through microscale deposition nozzles. Ink deposition into an alcohol/water coagulation reservoir yielded polyelectrolyte filaments that rapidly solidify to enable three-dimensional patterning of microperiodic structures with self-supporting features. The influence of ink and reservoir chemistry on the phase behavior, rheological properties, and assembly of concentrated polyelectrolyte complexes is reported with an emphasis on the optimal conditions for 3-D writing.     

Facile homogeneous hydrogenations of hindered olefins with [Ir(cod)py(PCy3)]PF6

The title complex readily hydrogenates a number of hindered steroidal olefin groups from the α face, without reducing ketone carbonyl groups, carbon—halogen bonds or cyclopropane rings.     

Free radical-mediated vinyl amination: access to N,N-dialkyl enamines and their beta-stannyl and beta-thio derivatives

[reaction: see text] The first examples of free radical-mediated vinyl amination are described by nonconventional vinyl radical addition to azomethine nitrogen. This new vinyl amination protocol is mild and provides convenient synthetic access to nonstabilized N,N-dialkyl enamines and tandem bond-forming processes.