Search results for "bond cleavage"
showing 10 items of 58 documents
Die unsymmetrischen Cyclooctadienine: 1,3‐Cyclooctadien‐5‐in und 1,6‐Cyclooctadien‐3‐in
1985
Verschiedene Varianten des synthetischen Zugangs zu den beiden Titelverbindungen 15 und 45 werden diskutiert. 15 und 45 konnen in situ umgesetzt werden. Fur die Isolierung in reiner Form ist ihre mittlere Lebensdauer zu gering. Sie isomerisieren sich auf der C8H8-Energiehyperflache zu Styrol (47) und/oder Benzocyclobuten (22).
Alcohol oxidation by dioxygen and aldehydes catalysed by square-planar cobalt(III) complexes of disubstituted oxamides and related ligands
2001
The square-planar cobalt(III) complexes of o-phenylenebis(N′-methyloxamidate) (Me2opba) and related oxamate (Meopba) and bis(oxamate) (opba) ligands catalyse the selective oxidation, by dioxygen and pivalaldehyde, of a wide range of secondary alcohols to the corresponding ketones, in good yields and under mild conditions in acetonitrile at room temperature. Thus, the oxidation of the series of α-alkylbenzyl alcohols PhCH(OH)R (R = Me, Et, iPr, tBu) results in the exclusive formation of ketones as a product of C−H bond cleavage, and no C−C bond cleavage products are observed in any case. The modulation of catalytic activity by ligand substituents among this series of cobalt catalysts highlig…
Thermo-oxidative stabilization of poly(lactic acid) with antioxidant intercalated layered double hydroxides
2016
Two antioxidant modified layered double hydroxides (AO-LDHs) were successfully prepared by the intercalation of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (IrganoxCOOH) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) in the layered structure of LDH. It was found that by anchoring the phenolic moieties to the LDH layers the antioxidant power is retained in the case of Trolox, and even amplified in the case of IrganoxCOOH. A small amount of the two AO-LDHs was incorporated into poly(lactic acid), PLA, by solution mixing and melt extrusion. The thermo-oxidative stability of the composites was compared with that of the neat PLA and PLA containing free AOs. SEC analy…
Two copper complexes from two novel naphthalene-sulfonyl-triazole ligands: different nuclearity and different DNA binding and cleavage capabilities.
2013
[EN] Two novel naphthalene-sulfonyl-triazole ligands, 5-amino-N1-(naphthalen-3-ylsulfony1)-1,2,4-triazole (anstrz) and 3,5-diamino-N1-(naphthalen-3-ylsulfony1)-1,2,4-triazole (danstrz), purposely designed to interact with DNA, have been prepared for the first time and then fully characterized by H-1, C-13 NMR and IR spectroscopy, mass spectrometry and elemental analysis. The crystal structures of two copper complexes of these derivatives, i.e. [Cu(anstrz)(4)(NO3)(2)]center dot 4CH(3)OH (1), mononuclear, and [Cu(danstrz)(mu-OAc)(2)](2)center dot 2(danstrz) (OAc = acetato) (2), dinuclear, have been determined by single-crystal X-ray diffraction. In both cases the ligand coordinates in a monod…
Electrical Conductivity and Luminescence in Coordination Polymers Based on Copper(I)-Halides and Sulfur-Pyrimidine Ligands
2011
The solvothermal reactions between pyrimidinedisulfide (pym(2)S(2)) and CuI or CuBr(2) in CH(2)Cl(2):CH(3)CN lead to the formation of [Cu(11)I(7)(pymS)(4)](n) (pymSH = pyrimidine-2(1H)-thione) (1) and the dimer [Cu(II)(μ-Br)(Br)L](2) (L = 2-(pyrimidin-2-ylamino)-1,3-thiazole-4-carbaldehyde) (2). In the later reaction, there is an in situ S-S, S-C(sp(2)), and C(sp(2))-N multiple bond cleavage of the pyrimidinedisulfide resulting in the formation of 2-(pyrimidin-2-ylamino)-1,3-thiazole-4-carbaldehyde. Interestingly, similar reactions carried out just with a change in the solvent (H(2)O:CH(3)CN instead of CH(2)Cl(2):CH(3)CN) give rise to the formation of coordination polymers with rather diffe…
N-doped carbon networks: alternative materials tracing new routes for activating molecular hydrogen.
2014
The fragmentation of molecular hydrogen on N-doped carbon networks was investigated by using molecular (polyaromatic macrocycles) as well as truncated and periodic (carbon nanotubes) models. The computational study was focused on the ergonicity analysis of the reaction and on the properties of the transition states involved when constellations of three or four pyridinic nitrogen atom defects are present in the carbon network. Calculations show that whenever N-defects are embedded in species characterized by large conjugated π-systems, either in polyaromatic macrocycles or carbon nanotubes, the corresponding H2 bond cleavage is largely exergonic. The fragmentation Gibbs free energy is affect…
Oxidative DNA cleavage induced by an iron(III) flavonoid complex: synthesis, crystal structure and characterization of chlorobis(flavonolato)(methano…
2006
A flavonol iron(III) complex, [Fe(flavonolato)(2)Cl(MeOH)], has been prepared. The compound has been characterized by X-ray crystallography, spectroscopy, magnetism and electronic paramagnetic resonance (EPR) at X- and Q-band. The geometrical environment around the metal is best described as rhombic distorted octahedral. This distortion has also been inferred from the magnetic measurements and from the EPR spectra at different temperatures, E/D(rhombicity parameter) approximately 0.06. The DNA cleavage activity of the iron(III) complex with and without ascorbate/hydrogen peroxide is reported. Mechanisms of the oxidative cleavage have been proposed when DNA strand scission is performed both …
Thermal and electrochemically assisted Pd-Cl bond cleavage in the d9-d9 Pd2dppm2Cl2 complex by Pd3 dppm3COn+ clusters (n = 2, 1, 0).
2007
A new aspect of reactivity of the cluster [Pd3(dppm)3(micro3-CO)]n+, ([Pd3]n+, n = 2, 1, 0) with the low-valent metal-metal-bonded Pd2(dppm)2Cl2 dimer (Pd2Cl2) was observed using electrochemical techniques. The direct reaction between [Pd3]2+ and Pd2Cl2 in THF at room temperature leads to the known [Pd3(dppm)3(micro3-CO)(Cl)]+ ([Pd3(Cl)]+) adduct and the monocationic species Pd2(dppm)2Cl+ (very likely as Pd2(dppm)2(Cl)(THF)+, [Pd2Cl]+) as unambiguously demonstrated by UV-vis and 31P NMR spectroscopy. In this case, [Pd3]2+ acts as a strong Lewis acid toward the labile Cl- ion, which weakly dissociates from Pd2Cl2 (i.e., dissociative mechanism). Host-guest interactions between [Pd3]2+ and Pd2…
Radical Polymerization of Styrene Controlled by Half-Sandwich Mo(III)/Mo(IV) Couples: All Basic Mechanisms Are Possible
2001
Density functional calculations of bond dissociation energies (BDEs) have been used as a guide to the choice of metal system suitable for controlling styrene polymerization by either the stable free radical polymerization (SFRP) or the atom transfer radical polymerization (ATRP) mechanism. In accord with the theoretical prediction, CpMo(eta(4)-C(4)H(6))(CH(2)SiMe(3))(2), 2, is not capable of yielding SFRP of styrene. Still in accord with theoretical prediction, CpMo(eta(4)-C(4)H(6))Cl(2), 1, CpMo(PMe(3))(2)Cl(2), 3, and CpMo(dppe)Cl(2) (dppe = 1,2-bis(diphenylphosphino)ethane), 4, yield controlled styrene polymerization by the SFRP mechanism in the presence of 2,2'-azobisisobutyronitrile (A…
Mechanistic Studies on the Metal-Free Activation of Dihydrogen by Antiaromatic Pentarylboroles
2012
The perfluoro- and perprotiopentaphenylboroles 1 and 2 react with dihydrogen to effect H-H bond cleavage and formation of boracyclopentene products. The mechanism of this reaction has been studied experimentally through evaluation of the kinetic properties of the slower reaction between 2 and H(2). The reaction is first-order in both [borole] and [H(2)] with activation parameters of ΔH(‡) = 34(8) kJ/mol and ΔS(‡) = -146(25) J mol(-1) K(-1). A minimal kinetic isotope effect of 1.10(5) was observed, suggesting an asynchronous geometry for H-H cleavage in the rate-limiting transition state. To explain the stereochemistry of the observed products, a ring-opening/ring-closing mechanism is propos…