Generation of [(IPr)Pd(PR2Cl)] complexes via P-Cl reductive elimination

Treatment of [(IPr)Pd(Cl)(2)(PR(2)H)] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; R = Cy, tBu, or 1-Ad) with NaN(SiMe(3))(2) generated isolable [(IPr)Pd(PR(2)Cl)] complexes (68-75%) that have been crystallographically characterized. The formation of these mixed-ligand Pd(0) species in this manner corresponds to an unusual net dehydrohalogenation/P-Cl reductive elimination sequence.     

Electrochemical Determination of Inorganic Contaminants in Automotive Fuels

This article critically reviews the electroanalytical methods developed for the determination of inorganic contaminants in automotive fuels. Topics include the methods applied to the analysis of liquid biofuels and liquid fossil fuels for which different strategies were developed based on analytes and sample matrices. Special attention is given to electrodes, detection techniques, and sample preparation protocols (when required). Analytes include anions such as chloride, sulfate and phosphate, and mainly metallic species such as sodium, potassium, magnesium, calcium, cadmium, copper, iron, lead, manganese, mercury, nickel, platinum, tin, vanadium, and zinc. Suggestions for future research are also presented.     

Zwitterionic Relatives of Cationic Platinum Group Metal Complexes: Applications in Stoichiometric and Catalytic σ‐Bond Activation

Zwitterionic platinum group metal complexes that feature formal charge separation between a cationic metal fragment and a negatively charged ancillary ligand combine the desirable reactivity profile of related cationic complexes with the broad solubility and solvent tolerance of neutral species. As such, zwitterionic complexes of this type have emerged as attractive candidates for a diversity of applications, most notably involving the breaking and/or forming of E? H and E? C σ bonds involving a main group element E. Important advances in ancillary ligand design are documented that have enabled the construction of platinum group metal zwitterions. Also summarized are the results of stoichiometric and catalytic investigations in which the reactivity of such zwitterions and their more traditionally employed cationic relatives in σ bond activation chemistry are compared and contrasted.     

The Fabrication and Characterization of a Nickel Nanoparticle Modified Boron Doped Diamond Electrode for Electrocatalysis of Primary Alcohol Oxidation

We report the fabrication of a Ni nanoparticle modified BDD electrode and its application in the electrocatalysis of primary alcohol electrooxidation. Modification was achieved via electrodeposition from Ni(NO₃)₂ dissolved in sodium acetate solution (pH 5). Characterization of the Ni‐modified BDD (Ni‐BDD) was performed using ex situ atomic force microscopy (AFM) and high resolution scanning electron microscopy (SEM) coupled with energy dispersive X‐ray spectroscopy (EDX). Large nanoparticles of nickel were observed on the BDD surface ranging 5 to 690 nm in height and 0.18 μm^?3 in volume, and an average number density of ca. 13×10⁶ nanoparticles cm^?2 was determined. The large range of sizes suggests progressive rather than instantaneous nucleation and growth. Electrocatalysis of ethanol and glycerol, was conducted in an alkaline medium using an unmodified BDD, Ni‐BDD and a bulk Ni macro electrode. The Ni‐BDD electrode gave the better electrocatalytic performance, with glycerol showing the greatest sensitivity. Linear calibration plots were obtained for the ethanol and glycerol additions over concentration ranges of 2.8–28.0 mM and 23–230 μM respectively. This gave an ethanol limit of detection of 1.7 mM and sensitivity of 0.31 mA/M, and the glycerol a limit of detection of 10.3 μM with a sensitivity of 35 mA/M.     

Copper determination in ethanol fuel samples by anodic stripping voltammetry at a gold microelectrode

A linear sweep anodic stripping voltammetric method was developed for copper determination in commercial ethanol fuel samples by using a gold microelectrode. Under the optimized conditions, a linear range from 0.05 to 1.0 μM was obtained, with detection limit of 22 nM. The method was employed to determine copper ions in six commercial ethanol fuel samples and the results were compared with those obtained by FAAS. This study showed that for most samples both methods produced concordant results. However, for two samples, copper is distributed in its labile and complexed forms leading to copper contents contrasting with those obtained by flame atomic absorption spectroscopy (FAAS). It was observed that acidification of the samples is a very efficient way to recover copper from its complexed forms. After acidification, the copper contents obtained were concordant with those obtained by FAAS. Thus, the method can be employed to the reliable copper determination in commercial ethanol fuel samples. Moreover, this is the first work providing some insights about copper speciation in commercial ethanol fuel samples.     

Determination of Nickel in Fuel Ethanol Using a Carbon Paste Modified Electrode Containing Dimethylglyoxime

A mercury-free electrode chemically modified with carbon paste containing dimethylglyoxime was used for determination of nickel in fuel ethanol. The instrumental parameters and composition of the modified paste were optimized. The analytical curve for nickel determination from 5.0 × 10⁻⁹ to 5.0 × 10⁻⁷ mol L⁻¹ was obtained using 25 min of accumulation time. The detection limit and amperometric sensitivity obtained for this method were 2.7 × 10⁻⁹ mol L⁻¹ and 5.2 × 10⁸ μA mol⁻¹ L, respectively. The values for nickel concentration in four commercial samples of fuel ethanol were obtained in the range of 1.1 × 10⁻⁸ to 6.9 × 10⁻⁸ mol L⁻¹. A comparison to graphite furnace atomic absorption spectrometry (GFAAS) was performed for nickel determination in commercial samples of ethanol.     

Diels-alder adducts of 5-alkynylcyclopentadienols with tetracyanoethylene and dimethyl acetylenedicarboxylate: An X-ray crystallographic study of unexpected rearrangement products

The Diels-Alder reaction of tetracyanoethylene (TCNE) with 1, 4-diethyl-5-(trimethylsilyl)ethynyl-2,3-diphenylcyclopentadien-5-ol (3a) occurs on the hydroxyl-bearing face of the diene and yields ultimately an imino lactone (5a), whereby the hydroxyl functionality has added across an exo nitrile linkage. TCNE and 5-(trimethylsilyl)ethynyl-1,2,3,4-tetraphenylcyclopentadien-5-ol (3b) behave analogously. In contrast, the [4 + 2] adduct of 3b with dimethyl acetylenedicarboxylate (DMAD) undergoes a dramatic skeletal rearrangement to generate the 1,4-cyclohexadiene (9) in which an alkynyl ketone moiety has migrated onto an ester-bearing carbon. The molecules 5a and 9 have been characterized by X-ray crystallography, and a mechanism for the skeletal rearrangement is proposed.