Indirect Detection of Short-lived Hydride Intermediates of Iridium N-Heterocyclic Carbene Complexes via Chemical Exchange Saturation Transfer (CEST) Spectroscopy

Indirect Detection of Short-lived Hydride Intermediates of Iridium N-Heterocyclic Carbene Complexes via Chemical Exchange Saturation Transfer (CEST) Spectroscopy Full article

Journal

The Journal of Physical Chemistry C
ISSN: 1932-7447

Output data

Year: 2019, Volume: 123, Number: 26, Pages: 16288-16293 Pages count : 6 DOI: 10.1021/acs.jpcc.9b04179

Authors

Knecht Stephan ^1,2 , Hadjiali Sara ¹ , Barskiy Danila A. ³ , Pines Alexander ³ , Sauer Grit ¹ , Kiryutin Alexey S. ^4,5 , Ivanov Konstantin L. ^4,5 , Yurkovskaya Alexandra V. ^4,5 , Buntkowsky Gerd ¹

Affiliations

1	Eduard-Zintl Institute for Inorganic and Physical Chemistry, TU Darmstadt, Darmstadt 64287, Germany
2	Department of Radiology, Medical Physics, Medical Center University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
3	Department of Chemistry, University of California at Berkeley, Berkeley, California 94720-3220, United States
4	International Tomography Center, Siberian Branch of the Russian Academy of Science, Novosibirsk 630090, Russia
5	Novosibirsk State University, Novosibirsk 630090, Russia

For the first time, chemical exchange saturation transfer (CEST) nuclear magnetic resonance (NMR) is utilized to study short-lived hydride intermediates in the catalytic cycle of an organometallic complex [Ir(IMes)(Py)3(H)2]Cl. These complexes are typically not observable by other NMR techniques because 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 solution, in situ and at room temperature. Understanding the spin dynamics in these complexes is necessary for enhancing the performance of the nuclear spin hyperpolarization technique signal amplification by reversible exchange. By eliminating [Ir(Cl)(IMes)(Py)2(H)2] and manipulating the spin system by radiofrequency irradiation, the nuclear spin singlet lifetime of the hydride protons was increased by more than an order of magnitude, from 2.2 ± 0.1 to 27.2 ± 1.2 s. Because of its simplicity and ability to unravel unobservable chemical species, the utilized CEST NMR approach has a large application potential for studying short-lived hydride intermediates in catalytic reactions.

Knecht S. , Hadjiali S. , Barskiy D.A. , Pines A. , Sauer G. , Kiryutin A.S. , Ivanov K.L. , Yurkovskaya A.V. , Buntkowsky G.
Indirect Detection of Short-lived Hydride Intermediates of Iridium N-Heterocyclic Carbene Complexes via Chemical Exchange Saturation Transfer (CEST) Spectroscopy
The Journal of Physical Chemistry C. 2019. V.123. N26. P.16288-16293. DOI: 10.1021/acs.jpcc.9b04179

Submitted:	May 3, 2019
Accepted:	Jun 6, 2019
Published online:	Jun 7, 2019
Published print:	Jul 5, 2019

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