Weiterentwicklung diffusionsspektroskopischer NMR-Methoden für metallorganische Schlüsselverbindungen
Development of diffusion spectroscopic NMR methods for key organometallic compounds.
by Anne-Kathrin Dr. Kreyenschmidt
Date of Examination:2023-04-27
Date of issue:2023-10-02
Advisor:Prof. Dr. Dietmar Stalke
Referee:Prof. Dr. Dietmar Stalke
Referee:Prof. Dr. Manuel Alcarazo
Referee:PD Dr. Michael John
Referee:Prof. Dr. Konrad Koszinowski
Referee:Prof. Dr. Daniel Jun.-Obenchain
Referee:Dr. Holm Frauendorf
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EnglishThis work has extended the development and application of NMR diffusion spectroscopic techniques for the determination of the molecular weight of compounds in solution. In the process, methylcyclohexane-d14 was added to the range of NMR-type solvents that can be used for the application of classical ECC-based molecular weight analysis. In a second part of the work, the classical ECC-MW method was applied to the study of bis(R,R'-benzoxazol-2-yl)methanide-based compounds, which are the focus of current research as a ligand system for stabilizing low-valent metal centers. In particular, the study focused on the comparison of aggregation behavior in the solid state and in solution. In the third part of the work, the problem of exclusion of heavy atom-containing compounds from ECC-MW analysis was addressed. Thus, the investigation of halogenated compounds by classical ECC shows a systematic underestimation of the molecular weight. This circumstance can be attributed to the fact that the majority of the classical ECCs were prepared on the basis of reference compounds consisting of atoms of the first three periods. To extend the scope of the classical ECCs, a correction factor Xkor was also introduced in this work, which corrects the molecular weight of compounds containing heavy atoms as a function of the molar Van der Waals density. With the introduction of the correction factor, the application range of the ECCs could be enlarged. This means that compounds with heavy atoms, such as transition metal centers, are now also accessible to diffusion spectroscopic molecular weight determination. The transition metal-bearing molecules investigated in this work range from simple cyclopentadienyl compounds to structurally more complex and preparatively important systems such as the catalysts of the Grubbs family.
Keywords: DOSY; NMR; Organometallic compounds; Molecular Weight Determination