Figure 5.

SABRE studies with the water-soluble CODDA/Ir SABRE catalyst (13/15) in 100% D₂O. (a) Thermally polarized reference ¹H NMR scan from the solution following activation with pH₂ in the presence of excess substrate (py); the spectrum is vertically scaled 5-fold compared to panel b, which shows two spectra exhibiting successful observation of SABRE enhancement after bubbling with 1 atm of pH₂ at ∼10 mT [total bubbling times of 210 s (30 s immediately prior to acquisition, green dashed curve) and 240 s (30 s immediately prior to acquisition, red solid curve) for the spectra, respectively], then transfer to 9.39 T for high-field acquisition (note that the green curve is shown horizontally offset by a fraction of a ppm to show the enhancement compared to the red curve). Corresponding peak enhancements were ∼25-fold and ∼32-fold for py in water with only 1 atm of pH₂ bubbling in the two spectra, using a catalyst concentration of 0.3 mM. The inset shows the corresponding hydride region. A separate experiment where SABRE was attempted using the standard Ir/IMes catalyst in deuterated water exhibited no SABRE enhancement (c). (Vertical scale for panel c is different from that of panels a and b.)