Synthesis,Characterization, and Theoretical Investigation of Two‐Coordinate Palladium(0) and Platinum(0) Complexes Utilizing π‐Accepting Carbenes

An elegant general synthesis route for the preparation of two coordinate palladium(0) and platinum(0) complexes was developed by reacting commercially available tetrakis(triphenylphosphine)palladium/platinum with π‐accepting cyclic alkyl(amino) carbenes (cAACs). The complexes are characterized by NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction. The palladium complexes exhibit sharp color changes (crystallochromism) from dark maroon to bright green if the C‐Pd‐C bond angle is sharpened by approximately 6°, which is chemically feasible by elimination of one lattice THF solvent molecule. The analogous dark orange‐colored platinum complexes are more rigid and thus do not show this phenomenon. Additionally, [(cAAC)₂Pd/Pt] complexes can be quasi‐reversibly oxidized to their corresponding [(cAAC)₂Pd/Pt]⁺ cations, as evidenced by cyclic voltammetry measurements. The bonding and stability are studied by theoretical calculations.     

Dative versus electron-sharing bonding in N-imides and phosphane imides R3ENX and relative energies of the R2EN(X)R isomers (E = N,P; R = H,Cl, Me,Ph; X = H,F, Cl)*

ABSTRACT

Quantum chemical calculations using density functional theory BP86 and M06-2X functionals in conjunction with def2-TZVPP basis sets have been carried out on the title molecules. The calculation results reveal that the N-imides R₃NNX are always clearly higher in energy than the imine isomers R₂NN(X)R. In the case of phosphane imides R₃PNX and the isomers R₂PN(X)R, the substituent R plays a critical role in determining their relative stabilities. When R is hydrogen or phenyl group, R₃PNX are always higher in energy than R₂PN(X)R but the former are more stable than the latter when R = Cl. Interestingly, the Me₃PNX and Me₂PN(X)Me are quite close in energy. The energy decomposition analysis suggests that the P–N bond in the phosphane imides R₃PNX (R = H, Cl, Me, Ph; X = H, F, Cl) should be described in terms of an electron-sharing single bond between two charged fragments R₃P⁺-NX^? that is supported by (R₃P)⁺←(NX)^? π-backdonation. The π-bond contributes 14–21% of the total orbital interactions while the σ-bond provides 60–68% of ΔE_orb.     

Optical guiding of a radially polarized laser beam for inverseCherenkov acceleration in a plasma channel

In a conventional inverse Cherenkov accelerator (ICA), the background neutral gas provides the necessary dispersion to maintain the synchronism between the drive laser and the accelerated electrons. A laser-driven ICA is susceptible to diffraction, and the acceleration length is limited to approximately a Rayleigh range (for a Gaussian beam). In this paper, an ICA configuration is proposed that avoids the laser diffraction limitation by employing a preformed plasma channel. It is shown that a radially polarized laser beam can be optically guided if the plasma density increases with radius-like r². Expressions for the guided axial and radial components of the laser field are derived, and a numerical example is discussed     

Quenching of Flame Propagation Through Endothermic Reaction

The propagation of a premixed laminar flame supported by an exothermic chemical reaction under adiabatic conditions but subject to inhibition through a parallel endothermic chemical process is considered. The temperature dependence of the reaction rates is assumed to have a generalised Arrhenius type form with an ignition temperature, below which there is no reaction. The heat loss through the endothermic reaction, represented by the dimensionless parameter , has a strong quenching effect on wave initiation and propagation. The temperature profile can have a front or a pulse structure depending on the relative value of the ignition temperatures and on the value of the parameters and , the latter represents the rate at which inhibitor is consumed relative to the consumption of fuel. The wave speed-cooling parameter () curves are determined for various values of the other parameters. These curves can have three different shapes: monotone decreasing, -shaped or S-shaped, with the possibility of having one, two or three different flame velocities for the same value of the cooling parameter .     

Instability,Rupture and Fluctuations in Thin Liquid Films: Theory and Computations

Journal of Statistical Physics - Thin liquid films are ubiquitous in natural phenomena and technological applications. They have been extensively studied via deterministic hydrodynamic equations,...     

The Employment of a Removable Chitosan‐Derivatized Polymeric Sensitizer in the Photooxidation of Polyhydroxylated Water‐Pollutants

The known O₂(¹?_g)‐sensitizer system Chitosan bounded Rose Bengal (CH‐RB), with Rose Bengal (RB) immobilized by irreversible covalent bonding to the polymer Chitosan (CH), soluble in aquous acidic medium, was employed in the photodegradation of three tri‐hydroxy benzene water‐contaminants (THBs). The system sensitizes the O₂(¹?_g)‐mediated photodegradation of THBs by a process kinetically favored, as compared to that employing free RB dissolved in the same solvent. Additionally the free xanthene dye, degradable by O₂(¹?_g) through self‐sensitization upon prolonged light‐exposure, is considerably protected when bonded to CH‐polymer. The polymeric sensitizer, totally insoluble in neutral medium, can be removed from the solution after the photodegradative cycle by precipitation through a simple pH change. This fact constitutes an interesting aspect in the context of photoremediation of confined polluted waters. In other words, the sensitizing system could be useful for avoiding to dissolve dyestuffs in the polluted waters, in order to act as conventional sunlight‐absorbing dye‐sensitizers. In parallel the interaction CH ‐ O₂(¹?_g) in acidic solution was evaluated. The polymer quenches the oxidative species with a rate constant 2.4 × 10⁸ M^?1 s^?1 being the process mostly attributable to a physical interaction. This fact promotes the photoprotection of the bonded dye in the CH‐RB polymer.     

The influence of process parameters on the characteristics of polyhydroxyalkanoates produced by mixed cultures

The characterization of polyhydroxyalkanoates (PHA) produced by mixed cultures is fundamental for foreseeing the possible final applications of the polymer. In this study PHA produced under aerobic dynamic feeding (ADF) conditions are characterized. The PHA produced shows a stable average molecular weight ([symbol: see text]) in the range (1.0-3.0) x 10(6), along three years of reactor operation. Attempts to improve the amount of PHA produced did not introduce significant variations on the values [symbol: see text]. Along this period, the polydispersity indices (PDI) were between 1.3 and 2.2. The use of different carbon sources allowed the tailoring of polymer composition: homopolymers of poly(3-hydroxybutyrate), P(3HB), were obtained with acetate and butyrate, whereas a mixture of acetate and propionate, and propionate and valerate, gave terpolymers of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), and 2-methyl-3-hydroxyvalerate (2M3HV). All of these PHA had [symbol: see text] between 2.0 x 10(6) and 3.0 x 10(6). Thermal characterization of the produced polymers showed values of glass transition temperature, melting temperature, melting enthalpy, and crystallinity slightly lower than those obtained for PHA from pure cultures. The introduction of a purification step during the polymer extraction process allowed the elimination of possible contaminants but did not significantly improve the polymer quality.     

Abelian Hermitian geometry

We study the structure of Lie groups admitting left invariant abelian complex structures in terms of commutative associative algebras. If, in addition, the Lie group is equipped with a left invariant Hermitian structure, it turns out that such a Hermitian structure is Kähler if and only if the Lie group is the direct product of several copies of the real hyperbolic plane by a Euclidean factor. Moreover, we show that if a left invariant Hermitian metric on a Lie group with an abelian complex structure has flat first canonical connection, then the Lie group is abelian.     

α‐Arylation/Heteroarylation of Chiral α‐Aminomethyltrifluoroborates by Synergistic Iridium Photoredox/Nickel Cross‐Coupling Catalysis

Direct access to complex, enantiopure benzylamine architectures using a synergistic iridium photoredox/nickel cross‐coupling dual catalysis strategy has been developed. New C(sp³)? C(sp²) bonds are forged starting from abundant and inexpensive natural amino acids.     

The [B3(NN)3]+ and [B3(CO)3]+ Complexes Featuring the Smallest π‐Aromatic Species B3+

We report the spectroscopic identification of the [B₃(NN)₃]⁺ and [B₃(CO)₃]⁺ complexes, which feature the smallest π‐aromatic system B₃⁺. A quantum chemical bonding analysis shows that the adducts are mainly stabilized by L→[B₃L₂]⁺ σ‐donation.