Kaiserslautern - Fachbereich Chemie
Refine
Year of publication
Document Type
- Doctoral Thesis (389)
- Article (39)
Language
- German (309)
- English (116)
- Multiple languages (3)
Has Fulltext
- yes (428)
Keywords
- Katalyse (14)
- Eisen (9)
- Infrarotspektroskopie (9)
- Apoptosis (8)
- Oxidativer Stress (8)
- Gasphase (7)
- Palladium (7)
- Polyphenole (7)
- Acrylamid (6)
- Heterogene Katalyse (6)
Faculty / Organisational entity
Spin Hamiltonian parameters of a pentanuclear Os Ni cyanometallate complex are derived from ab initio wave function based calculations, namely valence-type configuration interaction calculations with a complete active space including spin-orbit interaction (CASOCI) in a single-step procedure. While fits of experimental data performed so far could reproduce the data but the resulting parameters were not satisfactory, the parameters derived in the present work reproduce experimental data and at the same time have a reasonable size. The one-centre parameters (local matrices and single-ion zero field splitting tensors) are within an expected range, the anisotropic exchange parameters obtained in this work for an Os−Ni pair are not exceedingly large but determine the low-T part of the experimental χT curve. Exchange interactions (both isotropic and anisotropic) obtained from CASOCI have to be scaled by a factor of 2.5 to obtain agreement with experiment, a known deficiency of such types of calculation. After scaling the parameters, the isotropic Os−Ni exchange coupling constant is cm−1 and the D parameter of the (nearly axial) anisotropic Os−Ni exchange is −1, so anisotropic exchange is larger in absolute size than isotropic exchange. The negative value of the isotropic J (indicating antiferromagnetic coupling) seemingly contradicts the large-temperature behaviour of the temperature dependent susceptibility curve, but this is caused by the negative g value of the Os centres. This negative g value is a universal feature of a pseudo-octahedral coordination with configuration and strong spin-orbit interaction. Knowing the size of these exchange interactions is important because Os(CN) is a versatile building block for the synthesis of / magnetic materials.
Nucleophilic substitution of [(η5-cyclopentadienyl)(η6-chlorobenzene)iron(II)] hexafluorophosphate with sodium imidazolate resulted in the formation of [(η5-cyclopentadienyl)(η6-phenyl)iron(II)]imidazole hexafluorophosphate. The corresponding dicationic imidazolium salt, which was obtained by treating this imidazole precursor with methyl iodide, underwent cyclometallation with bis[dichlorido(η5-1,2,3,4,5-pentamethylcyclopentadienyl]iridium(III) in the presence of triethyl amine. The resulting bimetallic iridium(III) complex is the first example of an NHC complex bearing a cationic and cyclometallated [(η5-cyclopentadienyl)(η6-phenyl)iron(II)]+ substituent. As its iron(II) precursors, the bimetallic iridium(III) complex was fully characterized by means of spectroscopy, elemental analysis and single crystal X-ray diffraction. In addition, it was investigated in a catalytic study, wherein it showed high activity in transfer hydrogenation compared to its neutral analogue having a simple phenyl instead of a cationic [(η5-cyclopentadienyl)(η6-phenyl)iron(II)]+ unit at the NHC ligand.
The Griffith-Ley oxidation of alcohols to aldehydes and ketones is performed with either RuCl3 ⋅ (H2O)x or a highly stable, well-defined ruthenium catalyst and with cheap trimethylamine N-oxide (TMAO) as the oxygen source. The use of n-heptane as the solvent, which forms a second phase with TMAO and a part of the alcohol, allows the reactions to be performed with a minimum amount of catalyst. This results in high local concentrations and thus to very rapid conversions. Detailed quantum chemical calculations suggest, that the Griffith-Ley oxidation not necessarily requires high oxidation states of ruthenium but can also proceed with RuII/RuIV species.
Sulfinate salts have attracted considerable attentions due to their versatile reactivity. They have emerged as highly useful building blocks for the construction of all kinds of sulfonyl-group containing molecules, such as sulfones or sulfonamides, and for the construction of various carbon–carbon- and carbon–heteroatom-bonds via sulfur dioxide (SO2) extrusion. Herein, we want to summarize the latest developments in the synthesis of sulfinate salts. Both improvement of classical methods and the development of various novel protocols will be discussed. Also selected one-pot methods directly utilizing in situ generated sulfinate salts as intermediates will be covered in this review article.
A palladium-catalyzed three-component synthesis of α-arylglycines from benzoic acids, sulfonamides and glyoxylic acid is reported. This novel reaction offers straightforward access to the important arylglycine motif in good yields and high structural diversity. By replacing boronic with carboxylic acids as nucleophilic component, this method can be considered as a more sustainable version of the classical Petasis reaction for synthesis of arylglycines.
Enantiomerically pure, C2-symmetric 2,6-bis(pyrazol-3-yl) pyridine ligands were obtained by treatment of diethyl-2,6-pyridinedicarbonate with (1R,4R)-(+)-camphor in the presence of NaH followed by ring closure with hydrazine. After twofold N-alkylation at the pyrazole rings, the addition of iron(II) chloride led to the according pentacoordinate dichloridoiron(II) complexes. All intermediates of the ligand synthesis, the ligands bearing NCH3 and NCH2C6H5 groups and the derived iron(II) complexes were structurally characterized by means of X-ray structure analysis. In-situ reaction with iron(II) carboxylates resulted in the formation of iron(II) carboxylate complexes, which turned out to be highly active in the hydrosilylation of acetophenone. However, even at room temperature, the enantiomeric excess of the product 1-phenylethanol is poor. 57Fe Mössbauer spectroscopy gave an insight into the species formed during catalysis.
A highly water-dispersible heterogeneous Brønsted acid surfactant was prepared by synthesis of a bi-functional anisotropic Janus-type material. The catalyst comprises ionic functionalities on one side and propyl-SO3H groups on the other. The novel material was investigated as a green substitute of a homogeneous acidic phase transfer catalyst (PTC). The activity of the catalyst was investigated for the aqueous-phase oxidation of cyclohexene to adipic acid with 30 % hydrogen peroxide even in a decagram-scale. It can also be used for the synthesis of some other carboxylic acid derivatives as well as diethyl phthalate.
A novel method for the highly stereoselective synthesis of tetrahydropyrans is reported. This domino reaction is based on a twofold addition of enamides to aldehydes followed by a subsequent cyclization and furnishes fully substituted tetrahydropyrans in high yields. Three new σ-bonds and five continuous stereogenic centers are formed in this one-pot process with a remarkable degree of diastereoselectivity. In most cases, the formation of only one out of 16 possible diastereomers is observed. Two different stereoisomers can be accessed in a controlled fashion starting either from an E- or a Z-configured enamide.
The production of nylon-6.6 is one of the largest scale syntheses in industrial chemistry. The standard procedure is based on an energy consuming low-level conversion of cyclohexane to yield adipic acid in two steps that is converted to nylon-6.6 in a separate step. Therefore, there is a strong intent to optimize the synthetic route in an economic and ecologic matter. In this work, we present a one-pot oxygenation of cyclohexane with hydrogen peroxide and a µ4-oxido-copper cluster catalyst to yield dicarboxylic acids with adipic acid as the main product.