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61.
通过对广义簇合物生长的自调整模型的解析,得出了粒子在均匀几率密度场下簇合物生长形态的变化特征,揭示了表征其生长形态结构分式维数D的物理意义,同时考查了格子模型对簇合物生长形态的影响以及自调整模型的动力学行为。 相似文献
62.
V. V. Yanilkin N. I. Maksimyuk E. I. Strunskaya B. M. Garifullin Yu. M. Kargin 《Russian Chemical Bulletin》1993,42(8):1340-1343
The effect of the nature of organic electron transfer agents and of PtII, PdII, RhII, CoII, NiII, CuII, CrIII, MnII, TiIII, VIII, ZnII, and AgI metal ions on the kinetics of the homogeneous reduction ofgem-dichlorocyclopropanes has been studied. PtII, PdII, RhIII, CoII, and NiII ions accelerate this process, VIII and AgI ions exert practically no effect on the reduction rate, and the rest of the metal ions exhibit inhibitor properties.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1407–1410, August, 1993. 相似文献
63.
Nano-sized phosphine and pyridine ligands having tetraphenylphenyl-, m-terphenyl-, poly(benzylether) moieties were synthesized. These ligands showed a remarkable effect on homogeneous transition
metal catalyzed reactions. Pd(II) complexes with tetraphenylphenyl substituted pyridine ligands show high catalytic activities
for oxidation of ketones suppressing Pd black formation and maintains the catalytic activity for a long time. Rh(I) complex
catalysts with m-terphenyl substituted phosphine ligands showed remarkable rate acceleration in the hydrosilylation of ketones. In addition,
several phosphinocalixarene ligands were synthesized and their coordination studies with Pd(II), Pt(II), Ru(II), Ir(I), and
Rh(I) metals were documented. Ir(I) and Rh(I) cationic complexes with a 1,3,5-triphosphinocalix[6]arene ligand showed dynamic
behavior with size-selective molecular recognition. 相似文献
64.
Dalmo Mandelli Rafael A. Steffen Georgiy B. Shul''pin 《Reaction Kinetics and Catalysis Letters》2006,88(1):165-173
Summary Epoxidation of natural terpene (+)-carvone by the system consisting of a catalyst, oxalic acid (co-catalyst) and H2O2 (70% aqueous solution; oxidant) was studied and factorial design methods were applied for the optimization of this reaction.
A dinuclear manganese(IV) complex [LMn(O)3MnL](PF6)2 (L = 1,4,7-trimethyl-1,4,7-triazacyclononane) was used as a catalyst, and acetonitrile was employed as a solvent. An analysis
by methods of the complete 24 factorial design showed that an increase in the catalyst concentration gives a strong positive effect on the carvone conversion
and selectivity. Hydrogen peroxide has a smaller positive effect on the conversion, but at high concentration, H2O2 leads to some decrease in the selectivity. An increase in the oxalic acid concentration has a beneficial effect on the conversion,
but does not affect the selectivity. 相似文献
65.
锐钛相虫蛀状介孔二氧化钛的表征 总被引:3,自引:0,他引:3
0IntroductionMesostructuredtitania(TiO2)hasattractedagreatdealofattention,inviewofcontrolleddelivery,catalytic,photocatlytic,orenergyconversionapplica-tions犤1犦.Theuseoftitaniumisopropoxidebis-acetylace-tonateprecursors,combinedwithalkylphosphatean-ionicsurfactantsastemplate,ledtothefirstdocu-mentedpuremesoporousTiO2犤2犦.Insubsequentyears,moresyntheticstrategieshavebeendevelopedusingavarietyofstructure-directingagents,forexample,car-boxylicacids犤3犦,alkylamine犤4犦,aminium犤5犦,blockcop-o… 相似文献
66.
Helmut G. Alt 《Russian Chemical Bulletin》1995,44(1):1-8
Ansa metallocene dichloride complexes of titanium, zirconium, and hafnium can be activated by methyl aluminoxane (MAO) to give excellent catalysts for the homogeneous polymerization of ethylene and propylene. The symmetry of the corresponding metaliocene dichloride complexes is essential for the stereospecific polymerization of propylene (isotactic, syndiotactic or atactic). The application of fluorenyl groups instead of cyclopentadienyl groups greatly increases the activity of the catalysts. The first ansa bis(fluorenyl) complexes of zirconium and hafnium, (C13H8-C2H4-C13Hs)MCl2 (M = Zr, Hf), have been prepared. It was found that after the activation by MAO the zirconium derivative demonstrates a very high activity. Several model complexes are presented in order to discuss the mechanism of the polymerization.This paper was presented at the INEOS-94 Workshop The Modern Problems of Organometallic Chemistry (Moscow, May 21–27, 1994).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 7–14, January, 1995. 相似文献
67.
Mayr M Wurst K Ongania KH Buchmeiser MR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(5):1256-1266
The synthesis of novel 1,3-diaryl- and 1,3-dialkylpyrimidin-2-ylidene-based N-heterocyclic carbenes (NHCs) and their rhodium(i) and palladium(II) complexes is described. The rhodium compounds bromo(cod)[1,3-bis(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene]rhodium (7), bromo(cod)(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)rhodium (8) (cod=eta(4)-1,5-cyclooctadiene, mesityl=2,4,6-trimethylphenyl), chloro(cod)(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)rhodium (9), and chloro(cod)[1,3-bis(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene]rhodium (10) were prepared by reaction of [[Rh(cod)Cl](2)] with lithium tert-butoxide followed by addition of 1,3-dimesityl-3,4,5,6-tetrahydropyrimidinium bromide (3), 1,3-dimesityl-3,4,5,6-tetrahydropyrimidinium tetrafluoroborate (4), 1,3-di-2-propyl-3,4,5,6-tetrahydropyrimidinium bromide (6), and 1,3-di-2-propyl-3,4,5,6-tetrahydropyrimidinium tetrafluoroborate, respectively. Complex 7 crystallizes in the monoclinic space group P2(1)/n, and 8 in the monoclinic space group P2(1). Complexes 9 and 10 were used for the synthesis of the corresponding dicarbonyl complexes dicarbonylchloro(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)rhodium (11), and dicarbonylchloro[1,3-bis(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene]rhodium (12). The wavenumbers nu(CO I)/nu(CO II) for 11 and 12 were used as a quantitative measure for the basicity of the NHC ligand. The values of 2062/1976 and 2063/1982 cm(-1), respectively, indicate that the new NHCs are among the most basic cyclic ligands reported so far. Compounds 3 and 6 were additionally converted to the corresponding cationic silver(i) bis-NHC complexes [Ag(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(2)]AgBr(2) (13) and [Ag[1,3-bis(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene](2)]AgBr(2) (14), which were subsequently used in transmetalation reactions for the synthesis of the corresponding palladium(II) complexes Pd(1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene)(2) (2+)(Ag(2)Br(2)Cl(4) (4-))(1/2) (15) and Pd[1,3-bis(2-propyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene)(2)]Cl(2) (16). Complex 15 crystallizes in the monoclinic space group P2(1)/c, and 16 in the monoclinic space group C(2)/c. The catalytic activity of 15 and 16 in Heck-type reactions was studied in detail. Both compounds are highly active in the coupling of aliphatic and aromatic vinyl compounds with aryl bromides and chlorides with turnover numbers (TONs) up to 2000000. Stabilities of 15 and 16 under Heck-couplings conditions were correlated with their molecular structure. Finally, selected kinetic data for these couplings are presented. 相似文献
68.
Rosa M. Dominguez Gabriel Chuchani Jairo Quijano Luz Janeth Orozco Iliana Restrepo 《Reaction Kinetics and Catalysis Letters》1996,57(1):191-196
The pyrolysis kinetics of ethyl 3-hydroxy-3-methylbutanoate have been examined over the temperature range of 286–330°C and pressure range of 29–108 Torr. In a seasoned vessel and in the presence of the free radical inhibitor cyclohexene or toluene the reaction is homogeneous, unimolecular and obeys a first-order rate law. The elimination products are mainly acetone and ethyl acetate, and very small amounts of ethyl 3-butenoate, acetic acid, ethylene and H2O. The rate coefficient is expressed by the following equation: log k1(s–1)=(12.39±0.46)–(174.5±5.2) kJ mol–1 (2.303RT)–1. The mechanism appears to proceed via a six-membered cyclic transition state, where polarization of the (CH3)C(OH)+...-CH2COOCH2CH3 bond is rate determining. 相似文献
69.
Stahl SS 《Angewandte Chemie (International ed. in English)》2004,43(26):3400-3420
Selective aerobic oxidation of organic molecules is a fundamental and practical challenge in modern chemistry. Effective solutions to this problem must overcome the intrinsic reactivity and selectivity challenges posed by the chemistry of molecular oxygen, and they must find application in diverse classes of oxidation reactions. Palladium oxidase catalysis combines the versatility of Pd(II)-mediated oxidation of organic substrates with dioxygen-coupled oxidation of the reduced palladium catalyst to enable a broad range of selective aerobic oxidation reactions. Recent developments revealed that cocatalysts (e.g. Cu(II), polyoxometalates, and benzoquinone) are not essential for efficient oxidation of Pd(0) by molecular oxygen. Oxidatively stable ligands play an important role in these reactions by minimizing catalyst decomposition, promoting the direct reaction between palladium and dioxygen, modulating organic substrate reactivity and permitting asymmetric catalysis. 相似文献
70.
The crystallization process of a simple liquid upon slow cooling has been modeled by the Monte-Carlo method. The model contains 10,000 Lennard-Jones atoms in the model box with periodic boundary conditions. The model structure is investigated at different stages of crystallization using Delaunay simplices. The simplex belonging to one or another particular crystal structure was determined by the shape of the given simplex taking into account the shape of its neighboring simplices. Simplices typical of the fcc and hcp crystal structures, as well as of polytetrahedral aggregates, not typical of crystals, were studied. The analysis has shown that the “precursors” of a hcp structure are strongly dominating over the “precursors” of a fcc structure in liquid phase before the beginning of crystallization. When crystallization starts, small embryos of the fcc structure are observed; the simplices peculiar to hcp are present at that in great amount, but they are distributed over the sample more uniformly. As crystallization proceeds, the portion of the fcc phase grows faster than hcp. However, no unified crystal appears in our case of slow cooling of the model. A complex polycrystalline structure containing crystalline regions with multiple twinning, pentagonal prisms and elements of icosahedral structures arises instead. 相似文献