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61.
Dioumaev VK Yoo BR Procopio LJ Carroll PJ Berry DH 《Journal of the American Chemical Society》2003,125(29):8936-8948
A series of stable complexes, (PMe(3))(3)Ru(SiR(3))(2)(H)(2) ((SiR(3))(2) = (SiH(2)Ph)(2), 3a; (SiHPh(2))(2), 3b; (SiMe(2)CH(2)CH(2)SiMe(2)), 3c), has been synthesized by the reaction of hydridosilanes with (PMe(3))(3)Ru(SiMe(3))H(3) or (PMe(3))(4)Ru(SiMe(3))H. Compounds 3a and 3c adopt overall pentagonal bipyramidal geometries in solution and the solid state, with phosphine and silyl ligands defining trigonal bipyramids and ruthenium hydrides arranged in the equatorial plane. Compound 3a exhibits meridional phosphines, with both silyl ligands equatorial, whereas the constraints of the chelate in 3c result in both axial and equatorial silyl environments and facial phosphines. Although there is no evidence for agostic Si-H interactions in 3a and 3b, the equatorial silyl group in 3c is in close contact with one hydride (1.81(4) A) and is moderately close to the other hydride (2.15(3) A) in the solid state and solution (nu(Ru.H.Si) = 1740 cm(-)(1) and nu(RuH) = 1940 cm(-)(1)). The analogous bis(silyl) dihydride, (PMe(3))(3)Ru(SiMe(3))(2)(H)(2) (3d), is not stable at room temperature, but can be generated in situ at low temperature from the 16e(-) complex (PMe(3))(3)Ru(SiMe(3))H (1) and HSiMe(3). Complexes 3b and 3d have been characterized by multinuclear, variable temperature NMR and appear to be isostructural with 3a. All four complexes exhibit dynamic NMR spectra, but the slow exchange limit could not be observed for 3c. Treatment of 1 with HSiMe(3) at room temperature leads to formation of (PMe(3))(3)Ru(SiMe(2)CH(2)SiMe(3))H(3) (4b) via a CH functionalization process critical to catalytic dehydrocoupling of HSiMe(3) at higher temperatures. Closer inspection of this reaction between -110 and -10 degrees C by NMR reveals a plethora of silyl hydride phosphine complexes formed by ligand redistribution prior to CH activation. Above ca. 0 degrees C this mixture converts cleanly via silane dehydrogenation to the very stable tris(phosphine) trihydride carbosilyl complex 4b. The structure of 4b was determined crystallographically and exhibits a tetrahedral P(3)Si environment around the metal with the three hydrides adjacent to silicon and capping the P(2)Si faces. Although strong Si.HRu interactions are not indicated in the structure or by IR, the HSi distances (2.00(4) - 2.09(4) A) and average coupling constant (J(SiH) = 25 Hz) suggest some degree of nonclassical SiH bonding in the RuH(3)Si moiety. The least hindered complex, 3a, reacts with carbon monoxide principally via an H(2) elimination pathway to yield mer-(PMe(3))(3)(CO)Ru(SiH(2)Ph)(2), with SiH elimination as a minor process. However, only SiH elimination and formation of (PMe(3))(3)(CO)Ru(SiR(3))H is observed for 3b-d. The most hindered bis(silyl) complex, 3d, is extremely labile and even in the absence of CO undergoes SiH reductive elimination to generate the 16e(-) species 1 (DeltaH(SiH)(-)(elim) = 11.0 +/- 0.6 kcal x mol(-)(1) and DeltaS(SiH)(-)(elim) = 40 +/- 2 cal x mol(-)(1) x K(-)(1); Delta = 9.2 +/- 0.8 kcal x mol(-)(1) and Delta = 9 +/- 3 cal x mol(-)(1).K(-)(1)). The minimum barrier for the H(2) reductive elimination can be estimated, and is higher than that for silane elimination at temperatures above ca. -50 degrees C. The thermodynamic preferences for oxidative additions to 1 are dominated by entropy contributions and steric effects. Addition of H(2) is by far most favorable, whereas the relative aptitudes for intramolecular silyl CH activation and intermolecular SiH addition are strongly dependent on temperature (DeltaH(SiH)(-)(add) = -11.0 +/- 0.6 kcal x mol(-)(1) and DeltaS(SiH)(-)(add) = -40 +/- 2 cal.mol(-)(1) x K(-)(1); DeltaH(beta)(-CH)(-)(add) = -2.7 +/- 0.3 kcal x mol(-)(1) and DeltaS(beta)(-CH)(-)(add) = -6 +/- 1 cal x mol(-)(1) x K(-)(1)). Kinetic preferences for oxidative additions to 1 - intermolecular SiH and intramolecular CH - have been also quantified: Delta = -1.8 +/- 0.8 kcal x mol(-)(1) and Delta = -31 +/- 3 cal x mol(-)(1).K(-)(1); Delta = 16.4 +/- 0.6 kcal x mol(-)(1) and Delta = -13 +/- 6 cal x mol(-)(1).K(-)(1). The relative enthalpies of activation (-)(1) x K(-)(1)). Kinetic preferences for oxidative additions to 1 - intermolecular SiH and intramolecular CH - have been also quantified: Delta (H)SiH(add) = 1.8 +/- 0.8 kcal x mol(-)(1) and Delta S((SiH-add) =31+/- 3 cal x mol(-)(1) x K(-)(1); Delta S (SiH -add) = 16.4 +/- 0.6 kcal x mol(-)(1) and =Delta S (SiH -CH -add) =13+/- 6 cal x mol(-)(1) x K(-)(1). The relative enthalpies of activation are interpreted in terms of strong SiH sigma-complex formation - and much weaker CH coordination - in the transition state for oxidative addition. 相似文献
62.
Gary Kemister Addy Pross Leo Radom Robert W. Taft 《Journal of computational chemistry》1981,2(4):470-477
Ab initio molecular orbital theory with the STO -3G basis set is used to examine both charge and energy interactions in a series of meta- and para-substituted phenylborate anions and toluenes. Comparison of the results is made with data for substituted anilinium cations. It is concluded that whereas NH is a powerful σ acceptor, with essentially no π interaction, BH is primarily a π donor, and, to a slight extent only, a π donor. CH3 is indicated to be both a weak σ and π donor. Energies of interaction of BH and NH with a series of substituents are an order of magnitude larger than corresponding values for CH3. Interaction energies for BH are of opposite sign to those for NH. The results may be understood qualitatively using perturbation molecular orbital (PMO ) theory. 相似文献
63.
Avelina Ong-Lee Leo Sylvester Jan W. F. Wasley 《Journal of heterocyclic chemistry》1983,20(6):1565-1569
1,3,4,14b-Tetrahydro-2H,10H-pyrazino[1,2-α]pyrrolo[2,1-c] [1,4]benzodiazepines (1a-e) were synthesized to investigate their potential CNS activity. The key step in the synthesis was the formation of the 10,11-dihydro-5H-pyrrolo[2,1-c][1,4]benzodiazepine (13) by reduction and concomitant cyclization of the nitroketone (11). Biological evaluation of 1a-e revealed interesting properties for 1b (CGS 7525A) [2]. 相似文献
64.
Summary Aureomycin hydrochloride does not show any promise as a reagent for qualitative detection or quantitative estimation of any of the common cations or aidons. The well developed crystals of the rather insoluble nitrate may be used for the identification of aureomycin. The low solubility of the nitrate may give a better stability as compared with the hydrochloride, which would be of interest to the pharmacist.
Dedicated to Prof. Dr.Hans Lieb at his 70th birthday. 相似文献
Zusammenfassung Versuche mit Aureomycinhydrochlorid gaben keine Anhaltspunkte für eine Eignung dieser Verbindung als Reagens für die Auffindung oder Bestimmung der häufig angetroffenen Kationen oder Anionen. Die gut ausgebildeten Kristalle des wenig löslichen Nitrats können für die Erkennung von Aureomycin benützt werden. Die geringe Löslichkeit des Nitrats erhöht dessen Beständigkeit im Vergleich zum Hydrochlorid, was für Pharmazeuten von Interesse sein könnte.
Résumé Le chlorhydrate d'auréomycine ne montre aucune propriété intéressante comme réactif de recherche qualitative ou d'estimation quantitative des cations et anions courants. On peut utiliser les cristaux bien développés de son nitrate assez peu soluble pour identifier l'auréomycine. La faible solubilité de ce nitrate peut lui conférer une meilleure stabilité que celle du chlorure ce qui est digne d'intérêt pour les pharmaciens.
Dedicated to Prof. Dr.Hans Lieb at his 70th birthday. 相似文献
65.
A complete ro structure has been obtained for propadienone (CH2CCCO) with the aid of ab initio molecular-orbital calculations. The effect of electron correlation has been investigated using third order Møller-Plesset perturbation theory. The molecule is found to be planar bent (CCC145°) and the calculated structure yields rotational constants which are in good agreemant with experimental values. 相似文献
66.
Ab initio molecular orbital calculations with the STO-3G and 4-31G basis sets have been carried out for the neutral oxocarbons CnOn (n = 3, 4, 5, 6 and 7), the dianions CnOn2- (n = 3, 4, 5, 6 and 7), the monoanions CnOnH? (n = 3 and 4) and the related acids CnOnH2 (n = 3 and 4). Fully optimised geometries have been obtained for all species. The geometries, stabilities and acidities are discussed. 相似文献
67.
68.
Salter L Clifford T Morley N Gould D Campbell S Curnow A 《Journal of photochemistry and photobiology. B, Biology》2004,75(1-2):57-61
Comet assay data (tail DNA %) have been gathered for the concentration dependent role of three antioxidants (AOs); quercetin (Q), epigallocatechin gallate (EGCG) and N-acetylcysteine (NAC) in reducing UV-induced damage to DNA in normal fetal lung fibroblasts (MRC5). All three compounds demonstrate a concentration dependent reduction maximum with a pro-oxidant effect at higher (though not cytotoxic) concentrations. Manipulation of a simple 4-step reaction mechanism for free radical (FR) scavenging by AOs produced rate constant ratios which allowed the relative effectiveness (Q > EGCG > NAC) of the AOs to be evaluated. 相似文献
69.
Analyses of dioxins in food have become increasingly important since the European Commission has enforced maximal toxic equivalent concentration (TEQ) levels in various food and feed products. Screening methodologies are usually used to exempt those samples that are below the maximum permitted limit and that can, therefore, be released to the market. In addition, one needs to select those samples that require confirmation of their dioxin TEQ level. When bioassays are used as screening tools, the interpretation of the obtained results should consider the higher variability and uncertainty associated with them. This paper explores the use of CALUX data as quantitative screening results. The validation of the method for the polychlorinated dibenzo-p-dioxins (PCDD)/F TEQ determination in milk samples is described with emphasis on the decision limit (CC) and the precision of the method. The decision limit amounts to 4.53 pg TEQ/g fat. Repeatability and within-lab reproducibility coefficients of variation are below 30%. The newly introduced parameter CC* of 1.47 pg TEQ/g fat delimits with CC a range of suspicious results. These data are not significantly different from the maximum limit of 3 pg TEQ/g fat and should be confirmed by a confirmatory analytical method such as HRGC–HRMS. 相似文献
70.
Cycloprop [a] acenaphthylene was found to rearrange to phenalene in the presence of rhodium dicarbonyl chloride dimer. Deuterium labeling of this molecule at C(7) (both exo and endo), at C(8), at C(7) (exo) and C(8) and at C(7) (exo), C(8), and C(8') indicated that the C(7) (exo) deuterium was migrating stereospecifically. Furthermore, all of the isotopic label present in the cycloprop[a]acenaphthylene was found statistically distributed over positions 1, 3, 4, 6, 7, and 9 of the phenalene product. Control experiments established the need of the catalyst, the inability to achieve rearrangement of the exo-7-methyl derivative, and the susceptibility of a monodeuterated phenalene for extensive isotopic scrambling in its own right when exposed to rhodium(I). These results have been interpreted on the basis of oxidative addition by rhodium(I) into the central bond of cycloprop[a]acenaphthylene from above the “flap”, followed by shifting of the C(7) (exo) hydrogen (or deuterium) to give a η3-allylrhodim-(III) complex. The experimental data further support a mechanism involving subsequent rearrangement of this intermediate around the periphery of the phenalene ring. This process which is otherwise degenerate is thought to be facilitated by the special electronic features of the phenalenyl system. 相似文献