Cationic gold carbonyl complex on a phosphine support

A cationic gold carbonyl complex has been synthesized and characterized using several techniques including X-ray crystallography. [(Mes(3)P)Au(CO)][SbF(6)] (Mes = 2,4,6-Me(3)C(6)H(2)) has a linear, two-coordinate gold atom. This compound displays the CO stretching frequency at 2185 cm(-1). The (13)C NMR signal of the gold-bound (13)CO appears as a doublet centered at δ 182.6 ((2)J(C,P) = 115 Hz). A computational study shows that the Au-CO bond consists of electrostatic attraction, Au ← CO donation, and significant Au → CO π-back-bonding components. Polarization of the CO bond caused by the electrostatic effect of the cationic gold center is mainly responsible for the large blue shift in the CO stretching frequency.     

Rhodium- and palladium-catalyzed 1,5-substitution reactions of 2-en-4-yne acetates and carbonates with organoboronic acids

Two methods involving the rhodium-catalyzed reaction of 2-en-4-yne acetates and the palladium-catalyzed reaction of 2-en-4-yne carbonates with organoboronic acids were investigated; both afforded exclusively the (E)-configured vinylallenes. The coordinative interaction of the rhodium with the acetate group promoted the δ-elimination of Rh(I)-OAc from the alkenylrhodium intermediate II in both syn and anti modes, with the syn-elimination being the major path. DFT calculations revealed that a conformer of this intermediate (II), which can lead to the (E)-configured vinylallene product via the syn-elimination mode, is energetically the most favorable conformer. The rhodium-catalyzed procedure is not applicable to reactions involving (E)-configured enyne acetates, because the geometry of the alkenylrhodium intermediate that is derived from the corresponding (E)-enyne acetate would not allow such coordinative interaction to occur. The palladium-catalyzed method, which proceeds through formation of the σ-vinylallenylpalladium intermediate, B, is suitable for both the (E)- and (Z)-configured enyne carbonates and appears to have a wider scope for both organoboronic acids and enyne substrates. The palladium-catalyzed reaction of an enantiomerically enriched enyne carbonate proceeded with racemization.     

Synthesis, characterization and fluorescent property evaluation of 1,3,5-triaryl-2-pyrazolines

A series of 1,3,5-triaryl-2-pyrazolines was synthesized by dissolving the corresponding 4-alkoxychalcones in glacial acetic acid containing a few drops of concentrated hydrochloric acid. This step was followed by the addition of (3,4-dimethylphenyl) hydrazaine hydrochloride. Finally the target compounds were precipitated by pouring the reaction mixture onto crushed ice. The structures of the synthesized compounds were established by physicochemical and spectroscopic methods. The 1,3,5-triaryl-2-pyrazolines bearing homologous alkoxy groups were found to possess fluorescence properties in the blue region of the visible spectrum when irradiated with ultraviolet radiation. The fluorescent behavior of these compounds was studied by UV-Vis and emission spectroscopy, performed at room temperature.     

Evaluating Parallel Simulated Evolution Strategies for VLSI Cell Placement

Simulated Evolution (SimE) is an evolutionary metaheuristic that has produced results comparable to well established stochastic heuristics such as SA, TS and GA, with shorter runtimes. However, for optimization problems with a very large set of elements, such as in VLSI cell placement and routing, runtimes can still be very large and parallelization is an attractive option for reducing runtimes. Compared to other metaheuristics, parallelization of SimE has not been extensively explored. This paper presents a comprehensive set of parallelization approaches for SimE when applied to multiobjective VLSI cell placement problem. Each of these approaches are evaluated with respect to SimE characteristics and the constraints imposed by the problem instance. Conclusions drawn can be extended to parallelization of SimE when applied to other optimization problems.      

Tin(II) aminoalkoxides and heterobimetallic derivatives: the structures of Sn6(O)4(dmae)4, Sn6(O)4(OEt)4 and [Sn(dmae)2Cd(acac)2]2

Tin(II) methoxide reacts with N,N′‐dimethylaminoethanol (dmaeH) to yield Sn(dmae)₂ ( 1 ) along with small amounts of the hydrolysis product Sn₆(O)₄(dmae)₄ ( 2 ). The geometrically more regular iso‐structural cage Sn₆(O)₄(OEt)₄ ( 3 ) was obtained as the only tractable product isolated from reaction of 2 and Sb(OEt)₃, while 1 reacted with CdX₂ (X = acac, I) to afford Sn(dmae)₂Cd(acac)₂ ( 4 ) and Sn(dmae)₂CdI₂ ( 5 ). The X‐ray structures of 2, 3 and 4 are reported. Decomposition of 4 under aerosol‐assisted chemical vapour deposition conditions leads to amorphous tin oxide films with no detectable cadmium (i.e. ca < 2% cadmium), rather than a stoichiometric Sn:Cd oxide. Copyright © 2006 John Wiley & Sons, Ltd.     

Carbon-13 NMR chemical shift and electronic structure of polypeptide as studied by tight-binding MO theory: poly (β-benzyl L-aspartate) with the right-handle α-helix and left-handed α-helix forms

An attempt was made to calculate ¹³C NMR chemical shifts of poly(β-benzyl L-aspartate) having the right-handed α-helix (α_R-helix) and left-handed α-helix (α_L-helix) forms by a tight-binding MO sum-over-states theory within the extended Hückel framework, in order to examine whether or not the conformation-dependent ¹³C chemical shifts previously determined by the cross polarization-magic angle spinning technique are reproduced by a change of electronic structure of the polymer. It is found that the relative displacements of the observed C_α, C_β and carbonyl ¹³C chemical shifts between the α_R- and α_L-helices are reproduced qualitatively by the calculation.