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Knecht-Chemrxiv-Indirect Detection of Short-lived Hydride Intermediates of Iridium N-Heterocyclic Carbene Complexes via Chemical Exchange Saturation Transfer (CEST) Spectroscopy.pdf (2.79 MB)
Indirect Detection of Short-lived Hydride Intermediates of Iridium N-Heterocyclic Carbene Complexes via Chemical Exchange Saturation Transfer (CEST) Spectroscopy
Preprints are manuscripts made publicly available before they have been submitted for formal peer review and publication. They might contain new research findings or data. Preprints can be a draft or final version of an author's research but must not have been accepted for publication at the time of submission.
submitted on 23.04.2019 and posted on 24.04.2019by Stephan Knecht,, Sara Hadjiali, Danila Barskiy, Alexander Pines, Grit Sauer, Alexey S Kiryutin, Konstantin Ivanov, Alexandra V. Yurkovskaya, Gerd Buntkowsky
For the first time chemical-exchange saturation transfer (CEST) 1H NMR is utilized for the study of
short-lived hydride intermediates in the catalytic cycle of
the Iridium-based organometallic complex
[Ir(IMes)(Py)3(H)2]Cl, which are often not observable by
other NMR techniques, since they are low concentrated,
and undergo reversible ligand exchange with the main
complex. The intermediate complexes
[Ir(Cl)(IMes)(Py)2(H)2] and [Ir(CD3OD)(IMes)
(Py)2(H)2] are detected, assigned and characterized in situ
and at room temperature in solution. Understanding the
effects on the spin dynamics induced by these complexes
is necessary for enhancing the performance of the nuclear
spin hyperpolarization technique SABRE (Signal Amplification By Reversible Exchange). By eliminating
[Ir(Cl)(IMes)(Py)2(H)2] and manipulating the spin-system by RF-irradiation, we were able to increase the nuclear spin singlet lifetime of the two protons in the main
hydride complex by more than an order of magnitude,
from 2.2±0.1 s to 27.2±1.2 s. The presented CEST NMR
approach has a large application potential for studying
short-lived hydride intermediates in catalytic reactions.