Transmetalation of methyl groups supported by Pt(II)-Au(I) bonds in the gas phase, in silico, and in solution

We report Pt(II)-to-Au(I) methyl transfer reactions that occur in the gas phase and in solution. The heterobimetallic Pt(II)/Au(I) complexes {[(dmpe)PtMe(2)][AuPR(3)]}(+) (R = Me (2a), Ph (2b), (t)Bu (2c)), observed in the gas phase by means of electrospray ionization, were subjected to collision induced dissociation (CID) from which we could observe Pt-to-Au transmetalation along two reaction pathways involving formation of a Au-Me bond, analogous to those observed for the Pt(II)/Cu(I) complex recently reported. In the first pathway, neutral AuMe is generated with concomitant migration of PR(3) from Au(I) to the Pt(II) center, forming cation [(dmpe)PtMe(PR(3))](+) (R = Me (5a) or Ph (5b)). In the second pathway, the monophosphine stays attached to the gold center, yielding cation [(dmpe)PtMe](+) (7) and R(3)PAuMe. Quantitative energy-resolved collision induced dissociation experiments as well as density functional theory (DFT) calculations were used to investigate the potential surface involved in the transmetalation processes. Energy barriers of 22.3 and 47.9 kcal mol(-1) for the two reaction processes of 2b and of 45.4 kcal mol(-1) for the single reaction process of 2c were obtained. Parallel reactivity is observed in THF solution, allowing for a comparison of the product distributions with those observed in the gas phase, and the postulation of simple steric control of the branching ratio between the two pathways. DFT calculations at the M06-2X//BP86/TZP level were in good agreement with the experiments.     

A rapid multidimensional liquid-gas chromatography method for the analysis of mineral oil saturated hydrocarbons in vegetable oils

The present paper describes an investigation directed toward the development of a rapid heart-cutting LC-GC method for the analysis of mineral oil saturated hydrocarbons contained in vegetable oils. The automated LC-GC experiments were carried out by using a system equipped with a syringe-type interface, capable of both heart-cutting and comprehensive (LC × GC) two-dimensional analysis. The first dimension separation was achieved on a 100 mm × 3 mm ID × 5 μm d(p) silica column, operated under isocratic conditions (hexane). A single 30-s cut, corresponding to a 175 μL volume, was transferred to a programmed temperature vaporizer. After the large volume injection, the target analytes were separated in a rapid manner (~9 min) using a 15 m × 0.1mm ID × 0.1 μm micro-bore GC capillary. The overall LC-GC run time enables the analysis of ca. 4 samples/hour. Quantification was performed by using external calibration, in the 1-200 mg/kg range. The method was validated in terms of linearity, precision, limits of detection and quantification, and accuracy. A series of commercial samples were subjected to analysis. Various degrees of contamination were found in all samples, in the 7.6-180.6 mg/kg range.     

A Note on Krylov Methods for Fractional Evolution Problems

The solution of linear fractional-order differential problems is addressed. For this purpose, rational approximations obtained by projections on resolvent Krylov subspaces are considered. Their convergence properties in Hilbert spaces are investigated.     

X-ray study of the order—disorder transition in high-stage alkali metal intercalated graphite single crystals

Graphite intercalation compounds display a variety of structural properties because of their composite nature (graphite + intercalate) and their layered arrangement. Alkali metal intercalated graphite compounds undergo order-disorder phase transitions when the temperature is varied in the range 300–10 K. The disordered state shows true two-dimensional character, whereas three-dimensional coupling takes place on ordering. Results of single-crystal X-ray diffractometric and photographic studies of stage-2 KC₂₄ single crystals are presented. The positional and orientational correlations of the modulated liquid phase have been studied from 300 K down to the temperature transition T_u = 123.5° K. At the transition, the hexagonal incommensurate solid structure of the alkali metal is modulated by the graphite potential. This transition is discussed in terms of the relaxed-close packed structure model (Dicenzo, 1982). At low temperature a second transition takes place at T_L ≈ 95 K. It is found to correspond to the breaking of the 2D hexagonal symmetry of the K layer.     

Nanoelectromechanical systems

Nanoelectromechanical systems (NEMS) are nano-to-micrometer scale mechanical resonators coupled to electronic devices of similar dimensions. NEMS show promise for fast, ultrasensitive force microscopy and for deepening our understanding of how classical dynamics arises by approximation to quantum dynamics. This article begins with a survey of NEMS and then describes certain aspects of their classical dynamics. In particular, we show that for weak coupling the action of the electronic device on the mechanical resonator can be effectively that of a thermal bath, this despite the device being a driven, far-from-equilibrium system.     

The restarted shift‐and‐invert Krylov method for matrix functions

In this paper, the numerical evaluation of matrix functions expressed in partial fraction form is addressed. The shift‐and‐invert Krylov method is analyzed, with special attention to error estimates. Such estimates give insights into the selection of the shift parameter and lead to a simple and effective restart procedure. Applications to the class of Mittag–Leffler functions are presented. Copyright © 2012 John Wiley & Sons, Ltd.     

Electron Localization Dynamics in the Triplet Excited State of [Ru(bpy)3]2+ in Aqueous Solution

Hybrid DFT/classical molecular dynamics of the long‐lived triplet excited state of [Ru(bpy)₃]²⁺ (bpy=2,2′‐bipyridine) in aqueous solution is used to investigate the solvent‐mediated electron localization and dynamics in the triplet metal‐to‐ligand charge‐transfer (MLCT) state. Our studies reveal a solvent‐induced breaking of the coordination symmetry with consequent localization of the photoexcited electron on one or two bipyridine units for the entire length of our simulation, which amounts to several picoseconds. Frequent electronic “hops” between the ligands constituting the pair are observed with a characteristic time of approximately half a picosecond.     

Alternative precursors for MOVPE growth of InN and GaN at low temperature

We report on the use of dimethylhydrazine (DMHy) and tertiarybuthylhydrazine (TBHy), as alternative nitrogen precursor for GaN low-temperature growth, as well as to improve the InN growth rate. Lowering the GaN growth temperature, would allow growing InN/GaN heterostructures by MOVPE, without damaging the InN layers. Increasing the low InN MOVPE growth rate is of major importance to grow reasonably thick InN layers. In this respect, triethylindium (TEIn) was also used as an alternative to trimethylindium (TMIn).     

InN excitonic deformation potentials determined experimentally

We report the experimental determination of the interband deformation potentials of indium nitride by combining both optical spectroscopy investigations and high-resolution X-ray measurements performed on a series of InN films grown by metal organic vapour-phase epitaxy. Our approach, which follows the one used for GaN by Shan et al. [Phys. Rev. B. 54 (1996) 13460], gives here for InN a₁=−7.66 eV, a₂=−2.59 eV, b₁=5.06 eV, and b₂=−2.53 eV.     

A diastereoselective synthesis of both quercus lactone isomers employing allyl-type organometallics as key intermediates

Consecutive treatment of endo-butenyl potassium or endo-1-(tetrahydropyranyloxy)-exo-butenyl lithium with fluorodimethoxyboron and pentanal at ?75°C affords an erythro- and, respectively, threo-adduct, the hydrolysis and oxidation of which leads to the cis- and, respectively, trans-isomer of 5-butyl-4-methyl-tetrahydro-2-furanone (4-butyl-3-methyl-4-butanolide), 1, the so-called quercus or oak lactones.