Author : Jochen Matthes
Publisher :
ISBN 13 : 9783898206693
Total Pages : 168 pages
Book Rating : 4.2/5 (66 download)
Book Synopsis A Nuclear Magnetic Resonance Study in Gaseous, Liquid and Solid State of the Hydrogen Mobility and the Hydrogen Metal Interaction in Transition Metal Complexes by : Jochen Matthes
Download or read book A Nuclear Magnetic Resonance Study in Gaseous, Liquid and Solid State of the Hydrogen Mobility and the Hydrogen Metal Interaction in Transition Metal Complexes written by Jochen Matthes and published by . This book was released on 2004 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt: (English) The present thesis is dedicated to the analysis of the mobility and interaction of dihydrogen with and on transition metal complexes by NMR spectroscopy at solid, at liquid, and at gaseous phase. Aspects of homogeneous catalysis could be transferred on heterogeneous catalysis. The topic has been divided into four independent chapters. In the first chapter investigations on exchange coupling of coordinated dihydrogen in the synthesised dihydrogen complexes were undertaken. The HH distance of the coordinated dihydrogen ligand in these complexes is compared to others in a "medium" range, they should thus display a medium rotational tunneling frequency in the range of MHz. Until now, methods for determining tunneling frequencies of that order are unknown. Here was the method succesfully applied for the determination of the tunnelling frequency in the benzoic acid dimer, the low temperature solid state field cycling NMR relaxational method, tested for usage in transition metal complexes. A direct mechanism of relaxation, could not be observed. By measurement of the temperature dependent spin lattice relaxation times (T1) a trend with the HH distance in the complexes could be detected. While the two complexes with the same HH distance (1 and 2) show the same relaxation behaviour at low temperatures, complex 3, in which dHH is significantly shorter, shows a strong, levelling off in the T1 curve. This is an indication for a higher tunnelling frequency expected for shorter HH distances in complex 3. In chapter 2 the synthesised deuterated ruthenium complexes were measured by solid state 2H und 31P MAS NMR spectroscopy. With the help of lineshape analysis of the spectra, the quadrupolar interactions could be determined. Surprisingly in the sample of 5, two complexes and free deuterium with a chemical shift of 1.1 ppm instead of 4.5 ppm were found. The 16e- complex 5 reacts with free deuterium to the labile, saturated 18e- complex. The main part of the thesis deals with the phenomenon of the transition metal catalysed ortho para hydrogen conversion. Some transition metal complexes are known to catalyse the ortho/para hydrogen conversion, hydrogen isotope scrambling and hydrogenation reactions in liquid solution. Using the example of Vaska's complex IrClCO(PPh3)2, we show by NMR spectroscopy that the solvent is not necessary for these reactions to occur. Thus, solid frozen solutions or polycrystalline powdered samples of homogeneous catalysts may become heterogeneous catalysts. Comparative liquid and solid state studies provide novel insight into the reaction mechanisms. The last and forth part of the thesis focusses on the C-H activation in orthometallated ruthenium complexes. The synthesis of a rare example of a cis hydride ethene complex and its crystal structure are presented. The existence of this complex contrasts with the well functioning Murai catalysis, in which C-C coupling is achieved by reaction of orthometallated complexes with unsaturated hydrocarbons. With the help of theoretical calculations performed by Eric Clot (University of Montpellier, France) the unreactivity of this complex is explained. (german) Die Doktorarbeit widmet sich der Aufklärung von der Mobilität und der Wechselwirkung von Wasserstoffmolekülen in und an Übergangsmetall Komplexen mit Hilfe der NMR Spektroskopie in der Gasphase, flüssiger und in fester Phase. Die für die homogene Katalyse geltenden Aspekte konnten auf die heterogene Katalyse übertragen werden. Das Thema wird in vier unterschiedlichen Problemkomplexen bearbeitet. In dem erste Problemkomplex wird das Rotationstunneln in den synthetisierten Diwasserstoff Komplexen untersucht. Diese Komplexe, deren koordinierte, undissoziierte Wasserstoffmoleküle einen verglichen mit anderen Komplexen mittleren HH Abstand aufweisen, sollten eine mittlere Rotationstunnelaufspaltung im Bereich von MHz haben. Für diese Größenordung war bisher keine Bestimmungsmethode be
