The clean kinetic profile for this transformation permitted the determination of kobs values from single experiments using the integrated form of the bimolecular rate law and plotting 1/[1]t vs t; and we obtained a near identical kobs value of 35.2 M -1 hr -1 by this method (Table , entry 1; Figure ). Linear plots of X/[X]t vs t for derivatives of 1 (4, 5, and 7) in which both counter anion and aryl auxiliary were varied provided kobs values that revealed the kinetic impact of these variables via krel values (Table ). We observed a slight increase in kobs and a krel value of 1.2 when another "non-coordinating" counter anion, BF4 (4) was used (Table , entry 2). The use of diphenyliodonium derivative with a more basic counter anion, TFA (5), resulted in a decrease in kobs and a krel value of 0.52 (Table , entry 3). Our attempts to probe other counter anions (OTs and Cl) were unsuccessful due to the insolubility of these salts in acetonitrile even under relatively dilute conditions (0.05 M). However, in the case of diphenyliodonium chloride 6, the reaction mixture was heterogeneous at the outset of the reaction, but after extended reaction time (16 hours) became homogeneous. Analysis of the crude reaction mixture did reveal trace amounts of product 3 (as the chloride salt), but the major products were chlorobenzene and iodobenzene due to competitive ligand coupling of chloride anion (Table , entry 4). In the initial report by Karchava, the reaction conditions were optimized with 1, but the scope was performed with 7 bearing a mesityl "dummy" ligand. A comparison of the rate profile with 1 and 7 revealed that the phenylation of DABCO with 7 bearing a mesityl "dummy" ligand was substantially slower than that with 1 and a krel value of 0.33 was obtained (Table , entry 5). Taken together, these data suggest that both counter anion and aryl auxiliary are kinetically relevant variables, though the origin of their impact on kinetics is less clear at this stage. Analysis of pre-equilibria. The use of "non-coordinating" counter anions, such as triflate and tetrafluoroborate, is common place in modern reactions of diaryliodonium salts, but stands somewhat in contrast with the concept of a hypervalent bond. Although X-ray crystal structure data exists for compound 1 that shows pseudo T-shaped geometry with a relatively long O•••I contact of 2.93 Å, its solution state behaviour in a wide range of solvents is not well-described. Incidentally, the O•••I distance in hypervalent ArI(OTf)2 compound has recently been shown to be substantially shorter (cf. 2.14 Å) than the O•••I distance in 1. We therefore considered multiple forms of 1, which have long been the subject of debate (Scheme 3a). Compound 1 is often depicted in one of two forms and named accordingly: one involving a hypervalent bond, which is referred to as the "iodane" form and the other an ion pair between the diphenyliodonium cation 1′ and the corresponding anion, which is referred to as the iodonium salt form (Scheme 3a). Additionally, the product of the title reaction, 3, is a quaternary ammonium triflate salt (Scheme 3a). Therefore, we first assessed the solution state behaviour of 1 by comparing it with 3, and NaOTf. We measured the conductance (S/cm) of these three compounds, 1, 3, and NaOTf, in acetonitrile and observed very similar conductance profiles (Scheme 3b). Moreover, the dissociation constants for these salts derived from this data were very similar (0.015-0.026 M; Scheme 3b). The product 3 is the most dissociated ion pair and NaOTf is the least dissociated, though 1 has a very similar dissociation constant to NaOTf (cf 0.015 vs 0.016 M). These data suggest that in solution 1 is the "iodonium" form and exists as an equilibrium mixture of associated (non-conducting) and dissociated (conducting) ion pairs; however, we cannot rule out the existence of secondary (halogen or hypervalent) bonding in the associated ion pair form of 1. To further nail down the thermodynamic landscape of dissociation of 1 we measured the Kd(IOTf) values of 1 at several temperatures and constructed a van't Hoff plot (Scheme 3c). The enthalpy and entropy for dissociation can be obtained from the slope and intercept of the plot (Scheme 3c). The dissociation of diphenyliodonium triflate 1 was found to be endergonic (G) by 2.8 kcal/mol at 80 °C. Moreover, the enthalpy is 0.8 kcal/mol consistent with a weak secondary bond. With a more focused picture of the solution phase behaviour of 1, we turned our attention to the association complex A (Scheme 1b and 4). We used 1 H NMR spectroscopy to measure the association constant Ka(IN) by holding the concentration of 1 constant at 0.001 M and titrating in 2 (up to 20 equivalents) and observing changes in the chemical shift of the aromatic signals on the diaryliodonium cation; we obtained a value of 164 M -1 at 25 °C (Figure ). A dilute solution of 1 (0.001 M) in acetonitrile was intentionally used for these studies because the equilibrium between contact ions 1 and dissociated ions 1′ and -OTf exists almost exclusively (> 95%) as the dissociated ions 1′ and -OTf. Therefore, the binding constant measured by titrating in 2 is actually between 1′ and 2. We obtained Ka(IN) values at a range of temperatures to construct a van't Hoff plot and obtain the thermodynamic parameters (Scheme 4). The formation of complex A was found to be exergonic (G = -3.3 kcal/mol; Scheme 4). A comparison of the van't Hoff plots for dissociation of diaryliodonium triflate (Scheme 3c) and association between 1′ and 2 (Scheme 4) reveal that the enthalpy (-2.5 kcal/mol) and overall Gibbs free energy (-3.3 kcal/mol) of the I•••N secondary bond is larger than the enthalpy (-0.8 kcal/mol) and Gibbs free energy (-2.8 kcal/mol) of I•••O secondary bond. Overall, the difference in energy, between diphenyliodonium triflate 1 (contact ions) and the association complex A is relatively small (0.5 kcal/mol) and slightly favours A. Scheme 4. van't Hoff plot for binding of 1′ and 2.