Figure 4.

Comparison of the hydride regions of ¹H NMR spectra acquired during activation of the water-soluble CODDA/Ir SABRE catalyst 13 (a) and the conventional Ir/IMes SABRE catalyst 16 (b and c). (a) Upfield ¹H NMR region showing changes to the hydride resonances during activation of 13 in D₂O observed at 30, 60, and 180 s after pH₂ bubbling began (1 atm). A corresponding attempt to observe activation of the (poorly water-soluble) conventional SABRE catalyst in D₂O (16) exhibited no hydride signal (b). Selected spectra obtained separately during activation of 16 in deuterated methanol are shown in panel c, respectively, 60 and 420 s following the onset of pH₂ bubbling. As expected, activation of both 13 and 16 trend toward the same final hydride signal (i.e., a strong singlet at ∼22.8 ppm). Spectra in panels a–c possess different vertical scales.