The application of novel Ir-NHC polarization transfer complexes by SABRE

In recent years, the hyperpolarization method Signal Amplification By Reversible Exchange (SABRE) has developed into a powerful technique to enhance Nuclear Magnetic Resonance (NMR) signals of organic substrates in solution (mostly via binding to the nitrogen lone pair of N-heterocyclic compounds) by several orders of magnitude. In order to establish the application and development of SABRE as a hyperpolarization method for medical imaging, the separation of the Ir-N-Heterocyclic Carbene (Ir-NHC) complex, which facilitates the hyperpolarization of the substrates in solution, is indispensable. Here, we report for the first time the use of novel Ir-NHC complexes with a polymer unit substitution in the backbone of N-Heterocyclic Carbenes (NHC) for SABRE hyperpolarization, which permits the removal of the complexes from solution after the hyperpolarization of a target substrate has been generated

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

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