(viii) The first redox process by PhI(O)(OTf)2 proceeds with an overall activation energy of 21.7 kcal/mol (Figure ), which is comparable to that of 20.8 kcal/mol where the process is driven by Bi(4-CO2Etbipy)-HVI (Figure ). This result implies that these two reagents should have a very similar reactivity and the presence of the bipyridine ligand in the latter does not attenuate the oxidizing capacity of the iodine(V) center. This suggests that the presence of the bipyridine ligand allows for trapping of the in-situ-generated triflic acid, which considerably reduces the rate of decomposition of the sensitive ortho-quinone product, as shown in Table . Oxidation of p-nitrophenol by IBX. We recently investigated the mechanism of the double oxidation of phenols by IBX. 10a Figure depicts the free energy changes for the three key steps outlined in Table . The complete energy profile for the IBX-mediated the oxidation of p-nitrophenol is provided in the Supporting Information (Figure ). Consistent with the experimental findings (Table ), we found that unlike PhI(O)(OTf)2, the oxidation of p-nitrophenol by IBX requires a high overall activation barrier (30.9 kcal/mol). Since the carboxylate ligand within IBX coordinates more strongly than the triflate, both the ∆G2 and ∆G ‡ 1 values for IBX are computed to be greater than those for PhI(O)(OTf)2 (29_OTf). In addition, the larger ∆G1 value for IBX than PhI(O)(OTf)2 indicates that the former is thermodynamically more resistant to ligand exchange. It follows from these results that all three key steps (ligand exchange, hypervalent twist, and the redox step) contribute to the much lower reactivity of IBX toward oxidation of electron-deficient phenols. the Bi(N)-HVI oxidant and recovery of the starting material (Table , entry 8). This can be probed by DFT, which predicts that geometrical isomer 36 is ~12 kcal/mol more stable than the active oxidant 34 (Figure ). The latter is produced only after surmounting an activation barrier as high as 27.7 kcal/mol. The most stable isomer 34 is not reactive toward the ligand exchange process because the two active sites in this complex are blocked by the pyridine ligands. Specifically, in the most stable structure, the triflate ligands responsible for driving the ligand exchange occupy positions trans to the strong σ-donor phenyl and oxo ligands which renders this complex incapable of facilitating the oxidation. This hypothesis is supported by the highly unstable nature of intermediates 37 and 38 resulting from ligand exchange between 34 and ArOH. To summarize, the high stability of the inactive iodine(V) complex 34 does not allow ligand exchange to easily occur on such a system, and this is the likely reason for no reaction occurring between PhI(O)(Py)2(OTf)2 and p-nitrophenol. 11 Oxidation of p-nitro-phenol by Bi(4-OMebipy)-HVI. Finally, we wanted to understand why the yield of the oxidative reaction is reduced by replacing the 4,4'-ester substituents within Bi(4-CO2Etbipy)-HVI with strongly electron-donating 4,4'-dimethoxy moieties (Table , entries 1 and 7). From the DFT-derived mechanism illustrated in Scheme 1, we posit that the reaction between p-nitrophenol and Bi(4-OMebipy)-HVI should commence with the ligand exchange followed by protonation of the bipyridine ligand to give 19_OMe (Figure ). The overall activation free energy for these two key steps is computed to be only 10.1 kcal/mol. Based on the proposed mechanism, for the redox process to proceed, the protonated bipyridine ligand needs to dissociate from 19_OMe to give key intermediate 22_OTf. The presence of the electron-donating 4,4'-dimethoxy groups on the bipyridine ligand cause this key step to take place with an activation barrier of 25.1 kcal/mol, which is much more energy demanding in comparison to analogous process from 19 (18.8 kcal/mol, Figure ). The stronger coordination of the bipyridine ligand within 19_OMe than in 19 is evident from the shorter I-N bond distance in the former (2.336 Å) than in the latter (2.426 Å) (see Figures and).