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Long‐Term Generation of Longitudinal Spin Order Controlled by Ammonia Ligation Enables Rapid SABRE Hyperpolarized 2D NMR
Author(s) -
Vaneeckhaute Ewoud,
De Ridder Sophie,
Tyburn JeanMax,
Kempf James G.,
Taulelle Francis,
Martens Johan A.,
Breynaert Eric
Publication year - 2021
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.202100079
Subject(s) - spin isomers of hydrogen , chemistry , hyperpolarization (physics) , iridium , deuterium , carbene , singlet state , catalysis , chemical physics , photochemistry , hydrogen , nuclear magnetic resonance spectroscopy , stereochemistry , organic chemistry , atomic physics , physics , excited state
Symmetry breaking of parahydrogen using iridium catalysts converts singlet spin order into observable hyperpolarization. In this contribution, iridium catalysts are designed to exhibit asymmetry in their hydrides, regulated by in situ generation of deuterated ammonia governed by ammonium buffers. The concentrations of ammonia (N) and pyridine (P) provide a handle to generate a variety of stereo‐chemically asymmetric N‐heterocyclic carbene iridium complexes, ligating either [3xP], [2xP;N], [P;2xN] or [3xN] in an octahedral SABRE type configuration. The non‐equivalent hydride positions, in correspondence with the ammonium buffer solutions, enables to extend singlet‐triplet orS ⟩ → T 0 ⟩mixing at high magnetic field and experimentally induce prolonged generation of non‐equilibrium longitudinal two‐spin order. This long‐lasting magnetization can be exploited in hyperpolarized 2D‐OPSY‐COSY experiments providing direct structural information on the catalyst using a single contact with parahydrogen. Separately, field cycling revealed hyperpolarization properties in low‐field conditions. Controlling catalyst stereochemistry by introducing small and deuterated ligands, such as deuterated ammonia, simplifies the spin‐system. This is shown to unify experimental and theoretically derived field‐sweep experiments for four‐spin systems.