Advanced methodology for 103Rh NMR spectroscopy

Abstract

Despite the ubiquitous presence of rhodium complexes in catalysis, and the favourable 100% natural abundance of the spin-1/2 103Rh nucleus, 103Rh NMR parameters in the literature are notably sparse. This apparent dissonance is in part a consequence of the very low gyromagnetic ratio of 103Rh and hence its dismal NMR sensitivity. In this thesis, we aim to improve the accessibility of 103Rh NMR by developing advanced methodologies, which build upon existing techniques to improve 103Rh NMR sensitivity whilst simultaneously mitigating experimental hurdles associated with the practice. Furthermore, we will broaden the scope of 103Rh NMR by developing methodology to access and study the nascent singlet state in a 103Rh spin pair. To mitigate the poor sensitivity of the 103Rh nucleus, we demonstrate 1H enhanced 103Rh NMR methodology for the rapid acquisition of 103Rh NMR spectra and parameters; including 103Rh relaxation time constants over a range of magnetic fields. Moreover, a scheme is described for suppressing ringing artifacts, a common hurdle in the direct observation of low gyromagnetic ratio nuclei. We employ selective 18O labelling to break the magnetic equivalence of a 103Rh spin pair and facilitate the estimation of the 103Rh-103Rh J-coupling; as well as provide access to the 103Rh singlet state. We present the first measurement of an 18O induced 103Rh secondary isotope shift and report the first instance of singlet order generated in a 103Rh spin pair. The field dependence of both the relaxation of 103Rh longitudinal and singlet spin order is measured via field cycling experiments. We evaluate the rhodium formate paddlewheel complex as a vehicle for sustaining long lived 103Rh singlet order. Through the development of polarisation transfer techniques, we stand to greatly improve the accessibility, sensitivity and scope of the NMR technique for 103Rh nuclei in complexes that exhibit prerequisite heteronuclear scalar couplings.

More information

Identifiers

ORCID for Malcolm Levitt: orcid.org/0000-0001-9878-1180

Catalogue record

Export record