Early transition-metal perfluoroalkyl complexes

Elusive early transition-metal perfluoroalkyl complexes have been isolated and structurally characterized for the first time. Trifluoromethyltrimethylsilane, CF3SiMe3, serves as an excellent trifluoromethyl group-transfer reagent and reacts with the known Ti(IV) fluoride complex Cp2TiF2 to yield the novel Ti(IV) trifluoromethyl fluoride compound, Cp2Ti(CF3)(F) (1). Reaction of complex 1 with trimethylsilyltriflate (Me3SiOTf) affords the Ti(IV) trifluoromethyl triflate complex Cp2Ti(CF3)(OTf) (2). Both titanium perfluoroalkyl compounds have been characterized spectroscopically and by single-crystal X-ray analysis. The Ti-CF3 linkage in these complexes is remarkably robust and shows no evidence of an alpha-fluoride interaction (Ti...F-CF2) between the electrophilic Ti(IV) metal center and any of the C-F bonds in the trifluoromethyl group in the solid state or in solution.     

Spectrophotometric microdetermination of Cu(II) and Fe(III) using 2,4-dinitrosoresorcinol

The colored complexes formed by the reaction of dinitrosoresorcinol with Cu(II) and Fe(III) is utilized for the microdetermination of both metal ions either alone or in a binary mixtures. Satisfactory results are obtained when the proper media are utilized in the presence of an excess of the organic ligand. The interference of some ions is also investigated.     

Inside Cover: Challenging the Metallocene Dominance in Actinide Chemistry with a Soft PNP Pincer Ligand: New Uranium Structures and Reactivity Patterns (Angew. Chem. Int. Ed. 20/2009)

A standing iceberg illustrates how the soft PNP pincer ligand challenges the metallocene dominance (ship) in actinide chemistry, as described by J. L. Kiplinger and co‐workers in their Communication on page 3681 ff. Replacement of C₅Me₅ by the PNP ligand is a successful strategy for the promotion of new reactivities and to support new actinide structures. The specific electronic and steric properties of the PNP ligand enable access to structures not available for the C₅Me₅ ligand set and as yet unreported for uranium. (We thank Mr. Anthony Mancinco for the design of the graphic.)

     

Synthesis,structure, spectroscopy and redox energetics of a series of uranium(IV) mixed-ligand metallocene complexes

A series of uranium(IV) mixed-ligand amide–halide/pseudohalide complexes (C₅Me₅)₂U[N(SiMe₃)₂](X) (X = F (1), Cl (2), Br (3), I (4), N₃ (5), NCO (6)), (C₅Me₅)₂U(NPh₂)(X) (X = Cl (7), N₃ (8)), and (C₅Me₅)₂U[N(Ph)(SiMe₃)](X) (X = Cl (9), N₃ (10)) have been prepared by one electron oxidation of the corresponding uranium(III) amide precursors using either copper halides, silver isocyanate, or triphenylphosphine gold(I)azide. Agostic U?H–C interactions and η³-(N,C,C′) coordination are observed for these complexes in both the solid-state and solution. There is a linear correlation between the chemical shift values of the C₅Me₅ ligand protons in the ¹H NMR spectra and the U^IV/U^III reduction potentials of the (C₅Me₅)₂U[N(SiMe₃)₂](X) complexes, suggesting that there is a common origin, that is overall σ-/π-donation from the ancillary (X) ligand to the metal, contributing to both observables. Optical spectroscopy of the series of complexes 1–6 is dominated by the (C₅Me₅)₂U[N(SiMe₃)₂] core, with small variations derived from the identity of the halide/pseudohalide. The considerable π-donating ability of the fluoride ligand is reflected in both the electrochemistry and UV-visible-NIR spectroscopic behavior of the fluoride complex (C₅Me₅)₂U[N(SiMe₃)₂](F) (1). The syntheses of the new trivalent uranium amide complex, (C₅Me₅)₂U[N(Ph)(SiMe₃)](THF), and the two new weakly-coordinating electrolytes, [Pr₄N][B{3,5-(CF₃)₂C₆H₃}₄] and [Pr₄N][B(C₆F₅)₄], are also reported.     

Objective Voice Quality Analysis Before and After Onset of Unilateral Vocal Fold Paralysis

This study was designed to investigate objective voice quality measurements in unilateral vocal fold paralysis (UVFP) by eliminating intersubject variability. To our knowledge this is the first report objectively analyzing paralytic dysphonia as compared to the same voice before onset of UVFP. The voices of two male subjects were prospectively recorded before and after the onset of iatrogenic UVFP (thoracic surgery).The following acoustic measurements of the vowel /a/ were performed using the CSL and MDVP (Kay Elemetrics): jitter, shimmer, harmonics-to-noise ratio, cepstral peak prominence, the relative energy levels of the first harmonic, the first formant and the third formant, the spectral slope in the low-frequency zone (0-1 kHz and 0-2 kHz), and the relative level of energy above 6 kHz. Distribution of spectral energy was analyzed from a long-term average spectrum of 40 seconds of text. Laryngeal aerodynamic measurements were obtained for one patient before and after onset of paralysis using the Aerophone II (Kay Elemetrics). Pitch and amplitude perturbation increased secondary to UVFP, while the harmonics-to-noise ratio and the cepstral peak prominence decreased. A relative increase in the mid-frequency and high-frequency ranges and a decrease in the low-frequency spectral slope were observed. Mean airflow rate and intraoral pressure increased, and glottal resistance and vocal efficiency decreased secondary to UVFP. The findings of this self-paired study confirm some but not all the results of previous studies. Measures involving the fundamental and the formants did not corroborate previous findings. Further investigation with vocal tract modeling is warranted.     

Electrochemical Analysis of Acrylamide Using Screen‐Printed Carboxylated Single‐Walled Carbon Nanotube Electrodes

Acrylamide (AA) was electrochemically detected and quantified by means of its voltammetric response on carboxylic modified Single‐Walled Carbon Nanotube Screen Printed Electrodes (COOH‐SWCNT‐SPEs). The electroreduction signal of AA was proportional to AA concentration at low values (below 300 µM) and the observed sensitivity was explained in terms of AA adsorption on the COOH‐SWCNT‐SPEs that was demonstrated using the electrochemical response of [Fe(CN)₆]^3? and [Fe(CN)₆]^4? and Raman spectroscopy experiments. In order to test the suggested analytic approach (LOD of 0.03 µM, LOQ of 0.04 µM), detection and quantification of AA in fried potatoes was carried out using the proposed electrochemical method and HPLC. Both techniques showed similar contents of AA.     

Direct selective oxidation of benzene to phenol using molecular oxygen in the presence of palladium and heteropolyacids

The use of heteropolyacids as a reoxidant for palladium in the direct oxidation of benzene to phenol with molecular oxygen was studied as a function of the variables involved. It was shown that the oxidation system is very effective even if a molar ratio of HOAc:H₂O of 1:2 is used. After 4 h at 130°C the benzene conversion is 15% and the selectivity for phenol is above 70%. The quantity of palladium acetate can be drastically reduced allowing turnover numbers as high as 800.     

Dissipativity in impulsive systems via Lyapunov functions

This paper deals with impulsive dissipative semidynamical systems. We present sufficient conditions to obtain dissipativity for autonomous and non‐autonomous systems by using Lyapunov functions. Also, some converse‐type results are presented.     

Use of the interaction of a boronic acid with a merocyanine to develop an anionic colorimetric assay

A displacement assay based on the interaction of Brooker’s merocyanine (BM), a merocyanine dye, with an excess of phenylboronic acid (BA) was studied in acetonitrile. BM is colored in solution, but its reaction with BA yields a colorless covalently linked BA-BM species. This strategy was studied in the presence of different anions (F⁻, Cl⁻, Br⁻, I⁻, , , CH₃COO⁻, and ), but only fluoride, a strongly nucleophilic anion, and to a much lesser extent acetate, reacted with BA-BM, displacing BM through a bimolecular nucleophilic substitution mechanism, and coloring the solution. Experimental data were collected and are shown here in order to gain a better understanding of this chromogenic sensor.