Iridium mediated methyl and phenyl C-H activation of 2-(arylazo)phenols. Synthesis, structure, and spectral and electrochemical properties of some organoiridium complexes

Reaction of 2-(2′,6′-dimethylphenylazo)-4-methylphenol with [Ir(PPh₃)₃Cl] in refluxing ethanol in the presence of a base (NEt₃) affords an organoiridium complex 5, where the 2-(2′,6′-dimethylphenylazo)-4-methylphenol is coordinated to iridium, via C-H activation of a methyl group, as a dianionic tridentate C,N,O-donor. Two triphenylphosphines and a hydride are also coordinated to the metal center. A similar reaction carried out in toluene affords complex 5 along with a similar complex 7, where a chloride is coordinated to iridium instead of the hydride. Reaction of 2-(2′-methylphenylazo)-4-methylphenol with [Ir(PPh₃)₃Cl] in refluxing ethanol in the presence of a base (NEt₃) affords an organoiridium complex 12, where the 2-(2′-methylphenylazo)-4-methylphenol is coordinated to iridium, via C-H activation at the ortho position of the phenyl group in the 2′-methylphenylazo fragment, as a dianionic tridentate C,N,O-donor. Two triphenylphosphines and a hydride are also coordinated to the metal center. A similar reaction carried out in toluene affords a complex 12 along with a similar complex 13, where a chloride is coordinated to iridium instead of the hydride. Structures of complexes 5, 12 and 13 have been determined by X-ray crystallography. In all these complexes, the two triphenylphosphines are trans. All these complexes show intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows an Ir(III)-Ir(IV) oxidation within 0.60-0.73 V vs. SCE, followed by an oxidation of the coordinated 2-(arylazo)phenolate ligand within 1.08-1.39 V vs. SCE. A reduction of the coordinated 2-(arylazo)phenolate ligand is observed within −1.10 to −1.26 V vs. SCE.     

Potential energy curves for the X~1Σ_g~ , B~1△_g and B′~1Σ_g~ states of C_2 using MRCI and approximate CI methods

The potential energy curves for the X1Σ g , B1△g and B′1Σ g states of C2 have been studied by using MRC and approximate CI methods, and are benchmarked against the calculations of full configuration in teraction (FCI). The results obtained by MRCI method agree with the FCI very well, and even are accu rate enough to compare other approximate methods as benchmark, when the calculations of FCI ar not feasible. The approximate CI methods mentioned in this paper are reliable for treating chemica problems.     

Effect of the coordination sphere of d<Superscript>0</Superscript> metallocene on triplet-triplet energy transfer

The triplet nature of rare long-lived states of d⁰ metallocenes formed upon ligand-to-metal energy transfer was confirmed by studies of triplet-triplet charge transfer in biscyclopentadienyl complexes Cp₂MCl₂ (M = Zr (1), Hf (2)). The interaction between precatalysts and substrates of catalytic polymerization systems, viz., complexes 1 and 2 and unsaturated hydrocarbons (alkenes and dienes), was studied in the region of concentrations close to catalytic values. For organometallic π-complexes, it has been shown for the first time that, in the case of the unsaturated hydrocarbons, the efficiency of energy transfer obeys the Perrin equation. The process occurs at distances R ₀ close to the diameter of the interacting molecules and is well described by the exchange-resonant mechanism of interaction. In the case of the cyclopentadiene-Cp₂MCl₂ (M = Zr, Hf) systems, R ₀ = 14.6 Å. A linear relationship between the critical radius of the quenching sphere R ₀ and the number of carbon atoms in a linear α-olefin has been revealed for the first time and evidences the formation of a π-complex between the precatalyst and substrate molecules. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 35–39, January, 2007.     

Electrical conductance of CHCl3 solutions of polyethylene oxide doped with KCI

CHCl3 solutions containing a few percent polyethylene oxide PEO (M_W = 200 000) or the low-molecular model dioxane are stirred at 50°C during more than 100 h in the presence of small amounts of KCl. The specific conductance, the viscosity and the density of the solutions are measured at 25°C as a function of time. Both PEO and dioxane act as ligands improving the solubility of KCl. The relaxation times are of the order of several hours. After 40 h or more the viscosity of the solutions increases in a spectacular way. However, the most striking observation is that the specific conductance of the polymeric solutions at 25°C is systematically 5% higher than the value measured with the same sample at 45°C, just as for metals. The effect of the dilution of the primary stirred solutions either in the pure solvent or in the initial polymer solution is investigated. These results are discussed in terms of a three-step mechanism in the polymer systems: (1) Loading of the coils to polymeric cations with a full elementary charge, as a consequence of charge transfer interactions of the crown-ether type with numerous K⁺ ions penetrating into the coils; (2) Electron tunnelling conduction of the Hamill—Ceulemans type from one positive coil to the neighbouring one; (3) Alteration of the structure of the coils and of their hydrodynamic radius by the motions of K⁺ in the coils. These ‘brachiation’ motions by a hopping mechanism result from an increased mobility of the complexed K⁺ ions, which is also the origin of the Zundel effect. They do not directly contribute to the conductance but are responsible for the delayed increase of the viscosity.     

镍钴复合氧化物的制备和析氧活性

用浸碱热分解法制备了具有较高析氧活性和稳定性的复合氧化物ＮｉＣｏ＿２Ｏ＿４。考察了涂液成分、热分解温度和涂覆次数对ＮｉＣｏ＿２Ｏ＿４析氧活性的影响；测定了氧在ＮｉＣｏ＿２Ｏ＿４从电极上的稳态电化学行为。     

Thermochemistry of thermal plasma chemical reactions. Part I. General rules for the prediction of products

Equilibrium calculations based on the standard technique of minimization of the Gibbs free energy, with consideration of both gas and condensed phases, are shown to be inadequate for predicting the yield or even the proper composition of the products from thermal plasma reaction systems. This is due to the dominating influence of nucleation kinetics, a nonequilibrium effect.In this paper a modification of the equilibrium approach is proposed, whereby the supersaturation of a phase which may condense is calculated, and species with low supersaturation pressures which are unlikely to precipitate are subsequently removed from consideration.A comparison is made between the former equilibrium predictions and these quasi-equilibrium predictions. When compared with experimental data taken from the extant literature and from the authors' own research, the quasi-equilibrium modification is seen to provide excellent agreement with respect to product composition and yield. Examples are discussed including the thermal plasma production of hydrogen cyanide, ammonia, acetylene, silicon carbide, silicon nitride, and titanium carbide.     

Hydrogel networks of poly(ethylene oxide) star-molecules supported by expanded polytetrafluoroethylene membranes: characterization, biocompatibility evaluation and glucose diffusion characteristics

The present work discusses the grafting by electron beam irradiation of poly(ethylene oxide) (PEO) star-shaped polymers onto porous expanded polytetrafluoroethylene (EXPTFE) surfaces. The resulting materials are intended to combine the good biocompatible properties of PEO with the outstanding mechanical properties of PTFE. The star-shaped PEOs were synthesized via anionic polymerization. 3 Mev electron beam irradiation was applied to graft these PEO stars onto porous EXPTFE surfaces. The hydrophobic EXPTFE surface had to be pre-modified with N-vinylpyrrolidone. ESCA was used to quantify the amount of grafted star-shaped PEO. Unmodified EXPTFE surfaces are well known, when implanted in a body, to be rapidly covered by a layer of cells and fibrin. The EXPTFE coated with PEO were implanted in the peritoneal cavity of rats (or under the back skin). This implantation did not induce any inflammation reactions and SEM analysis had attested the absence of adsorbed cells and fibrin. The glucose diffusion properties of these membranes were studied by a lag time analysis method and compared to those of pure PEO hydrogels. As expected, glucose diffuses through the hydrogel coated membrane and diffusion is not affected by the presence of the EXPTFE membrane.     

表面修饰二氧化锡纳米微晶的制备与表征

制备了硅烷偶联剂KH-570表面修饰的SnO2纳米微晶，通过FT-IR、XPS、TEM和TG-DTA对其结构和表面特性进行表征和研究. FT-IR和XPS分析结果确证了KH-570与SnO2表面是以化学键合或物理吸附方式相结合,粒子表面存在酯基等有机官能团的红外吸收特征；观测到KH-570中Si原子的Si2s和Si2p谱线. TEM分析表明，表面修饰反应增强了SnO2纳米微晶的疏水性和分散性.由XPS和TG的实测数据探讨了纳米粒子具有较低包覆量的可能原因.     

Mo、W金属氧化物对CH4/CO2重整Ni基催化剂性能的影响

用XRD、XPS、元素分析、TEM和活性评价等方法研究过渡金属氧化物MoO3和WO3对SiO2负载的Ni基催化剂物理化学性质和CH4/CO2重整制合成气催化性能的影响.结果表明,在负载型的镍催化剂中,MoO3和WO3的添加一方面提高了Ni的核外电子密度,减弱了对CH4深度裂解积炭;另一方面使催化剂表面镍的相对浓度降低,结构上起到了隔离、分散金属颗粒的作用,氧的相对浓度升高,有效提高了催化剂的抗烧结和抗积炭能力,显示出较好的催化稳定性.     

What theoretical and/or chemical significance is to be attached to the magnitude of an activation energy determined for a solid-state decomposition?

This critical survey argues that the theory, conventionally used to interpret kinetic data measured for thermal reactions of initially solid reactants, is not always suitable for elucidating reaction chemistry and mechanisms or for identifying reactivity controls. Studies of solid-state decompositions published before the 1960s usually portrayed the reaction rate as determined by Arrhenius type models closely related to those formulated for homogeneous rate processes, though scientific justifications for these parallels remained incompletely established. Since the 1960s, when thermal analysis techniques were developed, studies of solid-state decompositions contributed to establishment of the new experimental techniques, but research interest became redirected towards increasing the capabilities of automated equipment to collect, to store and later to analyze rate changes for selected reactions. Subsequently, much less attention has been directed towards chemical features of the rate processes studied, which have included a range of reactants that is much more diverse than the simple solid-state reactions with which early thermokinetic studies were principally concerned. Moreover, the theory applied to these various reactants does not recognize the possible complexities of behaviour that may include mechanisms involving melting and/or concurrent/consecutive reactions, etc. The situation that has arisen following, and attributable to, the eclipse of solid-state decomposition studies by thermal analysis, is presented here and the consequences critically discussed in a historical context. It is concluded that methods currently used for kinetic and mechanistic investigations of all types of thermal reactions indiscriminately considered by the same, but inadequate theory, are unsatisfactory. Urgent and fundamental reappraisal of the theoretical foundations of thermokinetic chemical studies is now necessary and overdue. While there are important, but hitherto unrecognized, delusions in thermokinetic methods and theories, an alternative theoretical explanation that accounts for many physical and chemical features of crystolysis reactions has been proposed. However, this novel but general model for the thermal behaviour and properties of solids has similarly remained ignored by the thermoanalytical community. The objective of this article is to emphasize the now pressing necessity for an open debate between these unreconciled opinions of different groups of researchers. The ethos of science is that disagreement between rival theories can be resolved by experiment and/or discussion, which may also strengthen the foundations of the subject in the process. As pointed out below, during recent years there has been no movement towards attempting to resolve some fundamental differences of opinion in a field that lacks an adequate theory. This should be unacceptable to all concerned. Here some criticisms are made of specific features of the alternative reaction models available with the stated intention of provoking a debate that might lead to identification of the significant differences between the currently irreconciled views. This could, of course, attract the displeasure of both sides, who will probably criticise me severely. Because I intend to retire completely from this field soon, it does not matter to me if I am considered to be ‘wrong’, if it contributes to us all eventually agreeing to get the science ‘right’.