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Laura Tadiello

Development of low-field flow 31P NMR spectroscopy for reaction monitoring in organometallic chemistry

Universität Rostock, 2024

https://doi.org/10.18453/rosdok_id00004876

Abstract: Benchtop low-field (LF) NMR spectroscopy is a valuable tool for reaction monitoring and its application in catalysis. It is particularly attractive thanks to its low-cost and portability (i.e., the instrument can be installed right next to the fume hood). However, crucial quantitative results, e.g., kinetic profiles, cannot be correctly determined the moment degradation of an air- and moisture-sensitive catalyst occurs. Therefore, inertness of the entire setup must be guaranteed. In the first part of this thesis, it is demonstrated that this challenge could be overcome to meet the experimental requirements of highly oxygen-sensitive rhodium diphosphine complexes, relevant for homogeneous catalysis. Indeed, a commercially available benchtop LF NMR spectrometer has been evolved into an inert customized flow setup. Catalytic hydrogenation monitoring via LF 1H and 31P NMR spectroscopy proved to be suitable with this flow setup despite the relatively low concentration of the investigated species (ca. 10 mM). In the second part of the thesis, limitations due to the low magnetic field of the benchtop spectrometer (1.9 T) and the relative insensitivity of 31P compared to 1H nucleus have been faced. 31P NMR signal-to-noise ratios (SNRs) have been improved using advanced pulse sequences. Sensitive Homogeneous And Resolved PEaks in Real time (SHARPER) enhances 31P NMR signals by collapsing the target resonance into an extremely narrow singlet and eliminating the effects of field inhomogeneity. After demonstrating the advantage of this tool in static conditions (up to 10-fold enhancement factor on SNR), the customized on-line setup has been used to monitor a faster reaction (in the order of minutes), that could not be followed with traditional 31P NMR sequences.

doctoral thesis   free access