Kinetic Analysis. The coupling of diphenyliodonium triflate 1 and DABCO 2 was selected as a model reaction to study the mechanism of nucleophile arylation with diaryliodonium salts for several reasons. First, this reaction has recently been described in the literature and was shown to be highyielding (> 90%). Second, the nucleophile is a neutral molecule that does not require deprotonation therefore eliminating additional elementary steps in the mechanism and directing the full focus on elementary steps that involve the diaryliodonium salt. Third, the reaction is conducted in acetonitrile, in which diaryliodonium salts are relatively soluble, therefore enabling analysis of homogenous solutions by 1 H NMR spectroscopy. Moreover, the N-arylated product 3 is a linchpin intermediate for accessing diverse N-arylpiperidine derivatives that are key scaffolds of drugs (aripiprazole, Scheme 1a). The reaction conditions originally developed by Karchava and co-workers to synthesize 3 used two equivalents of 1 and a reaction time of 16 hours. We modified these conditions slightly to facilitate kinetic analysis by H NMR spectroscopy and found that stoichiometric quantities of 1 and 2 in a more dilute solution of MeCN-d3 (0.05 M) at 80 °C resulted in a high yield (96%) of 3 after 16 hours (Scheme 2a). Additionally, we observed that the formation of 3 is well-behaved over more than three half-lives and little to no by-products are observed (Scheme 2b and Figure ). We used variable time normalization analysis (VTNA) to determine the order in 1 and 2 and the observed rate constant (kobs) for the formation of 3 (Scheme 2c and Figure ). The reaction is first order in both 1 and 2, and under these conditions has a second order rate constant (kobs) of 35.3 M -1 hr -1 (Scheme 2c). Scheme 2. Model system for mechanistic analysis. a Conditions: 1 (0.1 mmol, 1 equiv.), 2 (0.1 mmol, 1 equiv.), MeCN-d3 (2 mL), 80 °C, 5-16 hours.