Hyperpolarization of Molecular Deuterium

ABSTRACT Hyperpolarized deuterium provides a promising alternative to hyperpolarized hydrogen for molecular sensing in NMR, particularly in hydrogen‐rich environments where proton detection is hindered by strong background resonances. Using a homogeneous iridium catalyst (IrIMes) and nicotinamide as substrate, we demonstrate the generation and detection of hyperpolarized molecular deuterium. The resulting resonance exhibits a pronounced partially negative line (PNL), strongly enhanced compared to thermal deuterium signal, and reproducible by simulation. A transient PNL is further observed during the initial phase of catalyst activation, highlighting sensitivity to transient intermediates. Notably, the enhanced PNL only arises in the presence of nicotinamide, confirming sensitivity to the presence of the substrate. These findings establish hyperpolarized orthodeuterium as a viable molecular sensor capable of providing valuable spectroscopic information of catalytic hydrogen‐bound complexes. Together with recent observations of PNLs in aqueous media, our results underscore the potential of hyperpolarized molecular deuterium to probe catalytic and enzymatic cycles under biologically relevant conditions.