Entry Acid PC Yield / % PC loading was next investigated as a discriminating parameter. The reaction using N-Cbz-proline 1a as starting material was therefore repeated at 1 mol%, 0.5 mol%, 0.25 mol% and 0.1 mol% (Table ). Yields remained largely the same for all three PCs down to 0.5 mol% (Table , entries 1-6). Contrastingly, differences in NMR yield were observed at 0.25 mol%, with 4CzIPN only achieving an average yield of 28% (Table , entry 7), while DiKTa and Mes3DiKTa maintained an average yield of 80% (Table , entries 8 and 9). When using 0.1 mol% PC loading, the use of both 4CzIPN and DiKTa produced poor average yields of 9% and 18%, respectively (Table , entries 10 and 11), while Mes3DiKTa achieved a significantly higher yield of 59% (Table , entry 12). The evidence suggests that DiKTa and Mes3DiKTa perform better than 4CzIPN at lower catalyst loadings, which is consistent with the higher molar absorptivity of DiKTa and Mes3DiKTa relative to 4CzIPN at the excitation wavelength used. Oxidative Quench. Subsequent studies assessed these PCs in an oxidative quenching process based upon the atom transfer radical addition (ATRA) reaction developed by Pirtsch et al. Using perfluorobutyl iodide 4a (Ep red = -1.42 V vs SCE in MeCN) and tert-butyl-N-allyl carbamate 5 as the substrates, 4CzIPN produced the desired ATRA product 6a in 83% yield (Table , entry 1). Interestingly, when using DiKTa and Mes3DiKTa, near quantitative yields of 97% and 93%, respectively, could be achieved ( and is commonly used in the literature; however, this value is erroneous and occurs only as a result of electrochemical degradation (Figure ). Indeed, a previous report by Bahamonde et al. found that the peak reduction potential is significantly more negative Ep red = -1.39 vs SCE in MeCN, and our own measurements have found it to be Ep