Iridium Pyridylpyrrolides Hyperpolarised by Para-Hydrogen.

Chemical activation of the nuclear singlet state of dihydrogen, para-hydrogen, can dramatically increase the sensitivity of magnetic resonance spectroscopy and imaging. Here, we show that the highly reversible activation of para-hydrogen by an iridium pyridylpyrrolide complex is capable of producing this hyperpolarisation effect. Bound alkene ligands exhibit signal enhancement without reduction to alkanes, which is in contrast to the most widely used hyperpolarisation catalysts. The complex is recoverable due to the highly reversible binding and release of H, and result in enhanced hydride signals in a wide range of coordinating and non-coordinating deuterated solvents. Synthetic modification of the ligand substituents and the addition of co-ligands show a strong dependence of chemical structure on reactivity, which reveals an untapped potential to exploit pyridylpyrrolides as ligands in the development of tunable para-hydrogen induced hyperpolarisation catalysts or molecular probes.