Facile Ar-CF3 bond formation at Pd. Strikingly different outcomes of reductive elimination from [(Ph3P)2Pd(CF3)Ph] and [(Xantphos)Pd(CF3)Ph

Facile and highly selective perfluoroalkyl-aryl reductive elimination from a metal center (Pd) has been demonstrated for the first time. At temperatures as low as 50-80 degrees C, [(Xantphos)Pd(Ph)CF3] undergoes remarkably clean decomposition to produce CF3Ph in high yield and selectivity. In contrast, analogous trifluoromethylpalladium aryls stabilized by rigid cis-chelating ligands such as dppe are completely unreactive at temperatures up to 130-140 degrees C. Decomposition of [(Ph3P)2Pd(Ph)CF3] in the presence of PhI in benzene at 60 degrees C does not produce PhCF3 but rather leads to [(Ph3P)2Pd(Ph)I] and [Ph4P]+[(Ph3P)Pd(CF3)3]- in a 2:1 ratio with high selectivity.     

A versatile new monomer family: functionalized 4-vinyl-1,2,3-triazoles via click chemistry

Using facile, highly modular synthetic approaches, a new monomer family based on a 1,2,3-triazole-4-vinyl building block has been prepared, and various functional derivatives have been obtained. Subsequent homo- and copolymerization of these novel functionalized monomers gives polymeric materials with unique physical properties, combining many attractive features of more traditional monomers, such as styrene, vinylpyridine, and meth/acrylates.     

Energy-resolved photoionization of alkylperoxy radicals and the stability of their cations

The photoionization of alkylperoxy radicals has been investigated using a newly developed experimental apparatus that combines the tunability of the vacuum ultraviolet radiation of the Advanced Light Source at Lawrence Berkeley National Laboratory with time-resolved mass spectrometry. Methylperoxy (CH(3)OO) and ethylperoxy (C(2)H(5)OO) radicals are produced by the reaction of pulsed, photolytically produced alkyl radicals with molecular oxygen, and the mass spectrum of the reacting mixture is monitored in time by using synchrotron-photoionization with a double-focusing mass spectrometer. The kinetics of product formation is used to confirm the origins and assignments of ionized species. The photoionization efficiency curve for CH(3)OO has been measured, and an adiabatic ionization energy of (10.33 +/- 0.05) eV was determined with the aid of Franck-Condon spectral simulations, including ionization to the lowest triplet and singlet cation states. Using the appearance energy of CH(3)(+) from CH(3)OO, an enthalpy of formation for CH(3)OO of Delta(f) (CH(3)OO) = (22.4 +/- 5) kJ mol(-1) is derived. The enthalpy of formation of CH(3)OO(+) is derived as Delta(f) = (1019 +/- 7) kJ mol(-1) and the CH(3)(+)-OO bond energy as (CH(3)(+) - O(2)) = (80 +/- 7) kJ mol(-1). The C(2)H(5)OO(+) signal is not detectable; however, the time profile of the ethyl cation signal suggests its formation from dissociative ionization of C(2)H(5)OO. Electronic structure calculations suggest that hyperconjugation reduces the stability of the ethylperoxy cation, making the C(2)H(5)OO(+) ground state only slightly bound with respect to the ground-state products, C(2)H(5)(+) and O(2). The value of the measured appearance energy of C(2)H(5)(+) is consistent with dissociative ionization of C(2)H(5)OO via the Franck-Condon favored ionization to the ? (1)A' state of C(2)H(5)OO(+).     

The electroanalytical detection of hydrazine: a comparison of the use of palladium nanoparticles supported on boron-doped diamond and palladium plated BDD microdisc array

We show that both a random distribution of palladium nanoparticles supported on a BDD electrode or a palladium plated BDD microelectrode array can each provide a sensing platform for the electrocatalytic detection of hydrazine. The palladium nanoparticle modified electrode displays a sensitivity and limit of detection of 60 mA mol(-1) L and 2.6 microM respectively while the array has a sensitivity of 8 mA mol(-1) L with a detection limit of 1.8 microM. The beneficial cost implications of using palladium nano- or micro-particles in sensors compared to a palladium macroelectrode are evident. Interestingly the array of the nanoparticles shows similar sensitivity and limit of detection to the microelectrode array which probably indicates that the random distribution of the former leads to 'clumps' of nanoparticles that effectively act as microelectrodes.     

Nonfluorinated volatile copper(I) 1,3-diketiminates as precursors for Cu metal deposition via atomic layer deposition

Novel nonfluorinated Cu(diketiminate)L complexes with L = neutral olefinic ligand have been prepared as stable, volatile Cu(I) precursors for the deposition of copper films by an atomic layer deposition (ALD) process. Among them, the complexes of 4-a and 5-a are the most volatile and stable at low temperature (55 degrees C). A clean, conformal copper film was deposited at 120 degrees C in an ALD process. These Cu(I) complexes are the first examples of nonfluorinated copper(I) diketiminates that can be readily applied to an industrial microelectronic fabrication process.     

Theoretical characterization of the "very rapid" Mo(V) species generated in the oxidation of xanthine oxidase

Density functional theory calculations of the "very rapid" Mo(V) intermediate of xanthine oxidase (XO) result in a square pyramidal geometry with end-on coordination of the model substrate. The Mo-C8 distance is 3.18 A, longer than previously reported from ENDOR experiments (<2.4 A Howes; et al. Biochemistry 1996, 35, 1432; 2.7-2.9 A Mandikandan; et al. J. Am. Chem. Soc. 2001, 123, 2658). Theoretical gas-phase isotropic hyperfine coupling constants A(iso)(C8) (B3LYP/BSII, 7.68 MHz; B3P86/BSII, 8.64 MHz) compare well with experimental values for the "very rapid" Mo(V) intermediate of XO with xanthine (8.8 MHz, Howes et al.) and 2-hydroxy-6-methylpurine (7.9 MHz, Mandikandan et al.). Absolute values of A(iso) of the metal-bound substrate oxygen are similar in magnitude to that of experiment.     

Redox control within single-site polymerization catalysts

The activity of a single-site titanium-based lactide polymerization initiator supported by a ferrocenyl-derivatized salen ligand is shown to be modulated by a chemical redox switch; a substantially higher rate of propagation is found for the neutral catalyst compared to its oxidized dicationic ferrocenium counterpart.     

TiCl3-enhanced NaAlH4: impact of excess al and development of the Al1-yTiy phase during cycling

NaAlH(4) with TiCl(3) and Al were mixed by ball-milling and cycled three times. The hydrogen storage properties were monitored during cycling, and the products were characterized by synchrotron X-ray diffraction. Because of the previously described formation of Al(1)(-)(y)Ti(y) with y approximately 0.15 during cycling that traps Al beyond the amount associated with the formation of NaCl, some Na(3)AlH(6) has no free Al to react with to form NaAlH(4). This was counteracted in the present work by adding a stoichiometric amount of Al that increases the theoretical storage capacity. Due to limitations in metal diffusion small amounts of Na(3)AlH(6) were still detected. When approximately 7 mol % more Al than the stoichiometric amount was added, the observed storage capacity increased significantly, and the Na(3)AlH(6) content was negligible after prolonged rehydrogenation. Cycled NaAlH(4) + 10 mol % TiCl(3) were desorbed to two different levels, and the diffraction patterns were compared. There is no change in unit-cell dimensions during desorption, and there is no sign of changes in the bulk composition of the Al(1)(-)(y)Ti(y) phase during a cycle. Adding pure Ti to a NaH + Al mixture by ball-milling in argon or hydrogen results in formation of TiH(2) that is stable during at least one cycle.     

Strong solutions of the Boltzmann equation in one spatial dimension

For the Boltzmann equation, the setting of a narrow shock tube implies that solutions $f(x,v,t)$ depend upon $v\in {\mathbb{R}}^3$, however they have one-dimensional spatial dependence. This Note discusses the case in which solutions are periodic in x, with controlled total energy and entropy, and such that the macroscopic density determined by the initial data is bounded. Our principal result is that the macroscopic density then remains bounded at all subsequent times, that is, this data gives rise to strong solutions which exist globally in time. Through a weak/strong uniqueness principle, these solutions are unique among the class of dissipative solutions. Additionally, we show that the flow of the Boltzmann equation propagates the moments in $v\in {\mathbb{R}}^3$ and derivatives in both $x_1\in {\mathbb{R}}^1$ and $v\in {\mathbb{R}}^3$ of the solution $f(x,v,t)$. Our main theorems are valid for Boltzmann collision kernels which are bounded, and which have a relative velocity cutoff. The proofs depend upon a new averaging property of the collision operator and integral inequalities based in turn on entropy and on the Bony functional. To cite this article: A. Biryuk et al., C. R. Acad. Sci. Paris, Ser. I 342 (2006).     

Alternate strip-based substructuring algorithms for elliptic PDEs in two dimensions

^** Email: angela.mihai{at}strath.ac.uk^*** Email: alan.craig{at}durham.ac.uk The alternate strip-based substructuring algorithms are efficientpreconditioning techniques for the discrete systems which arisefrom the finite-element approximation of symmetric ellipticboundary-value problems in 2D Euclidean spaces. The new approachis based on alternate decomposition of the given domain intoa finite number of strips. Each strip is a union of non-overlappingsubdomains and the global interface between subdomains is partitionedas a union of edges between strips and edges between subdomainsthat belong to the same strip. Both scalability and efficiencyare achieved by alternating the direction of the strips. Thisapproach generates algorithms in two stages and allows the useof a two-grid V cycle. Numerical estimates illustrate the behaviourof the new domain decomposition techniques.