Figure 3.

(a) Typical ¹H NMR spectrum from the hydride region of PVP comb polymer SABRE catalysts (PVPCs), exhibiting emissive and absorptive character for the three spectral regions of interest; spectrum was acquired in situ during catalyst activation, following ∼330 s of total pH₂ bubbling. (b) Selected spectra taken from the same spectral region of TiO₂/PMAA core–shell nanoparticle catalysts (NPCs), acquired with varying durations of pH₂ bubbling during catalyst activation and use (note the significantly greater spectral complexity). (c) Typical ¹H NMR spectrum from the same spectral region of a homogeneous variant of the SABRE catalyst, with 4-aminopyridine bound to Ir in the preactivated structure.^59,73 The spectrum was acquired in situ during catalyst activation, following ∼150 s of total pH₂ bubbling. (d) Plots showing the decay (normalized integrated NMR signal in magnitude mode) of intermediate species in spectral regions of ∼(−)12.4 ppm and ∼(−)17.2 ppm for the data in (b), along with corresponding data showing the rise of HP Ir-hydride resonances at ∼(−)22.8 ppm—likely indicating the presence of activated catalyst. The trend lines/eye guides are exponential fits. Data points taken at 450 s and earlier were acquired with in situ (high-field) bubbling within the magnet (filled symbols); later points were acquired with ex situ (low-field) bubbling and subsequent sample transfer to the NMR magnet (and thus the ex situ signals may be weaker because of relaxation during sample transit).