Реферат: A recently discovered method for significantly increasing the sensitivity of nuclear magnetic resonance (NMR) is based on the use of para-hydrogen with organometallic iridium complexes. This is a game-changing development in the field. This method, known as Signal Amplification by Reversible Exchange (SABRE), has rightfully attracted a lot of attention in recent years. The most commonly used precursor in SABRE is the [IrIMes(COD)Cl] complex, which forms stable dihydride species [Ir(IMes)Py3H2]Cl (see Figure 1). This plays a key role in transferring polarization from hydrogen to nuclei of the substrate (Py), enabled by interactions with hydrogen and an electron-pair donor substrate. IMes denotes 1,3-dimesitylimidazol-2-ylidene, COD is 1,5-cyclooctadiene, and Py is pyridine. Our study investigates an iridium hydride complex with pyridine in an aqueous medium, which remains stable for several days in water. We measured the magnetic field dependence of T1-relaxation times of individual protons of this complex using high-resolution NMR and a specialized setup designed for rapid sample positioning along the axial axis of the cryomagnet. Figure 1 clearly shows that the T1 dependence on the magnetic field has distinctive features at high magnetic fields. We determined the rotational correlation times of individual protons in the complex using a simplified model. The employed model focuses on the relaxation caused by fluctuating local fields, and it is sufficient in this case to obtain the correlation times of rotational motion. The τc values obtained are summarized in Table 1 of Figure 1, which clearly demonstrates statistically significant differences in the molecular mobility of various protons. Specifically, the Ha protons in the five-membered ring of the IMes ligand exhibit slower motion (τc = 440 ps) compared to protons in the more flexible six-membered rings of mesitylene (τc = 240 ps). References R. W. Adams, J. A. Aguilar, K. D. Atkinson, M. J. Cowley, P. I. P. Elliott, S. B. Duckett, G. G. R. Green, I. G. Khazal, J. Lopez-Serrano, D. C. Williamson, Science 2009, 323, 1708. Acknowledgements This work was supported by the Russian Science Foundation (grant number #23-73-10103).

Библиографическая ссылка: Kiryutin A.S. , Fishman N.N. , Yurkovskaya A.V.
Fast motions of an iridium dihydride complex in aqueous medium revealed by NMR relaxometry with high-resolution
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