Mechanistic Insights of a Concerted Metalation–Deprotonation Reaction with [Cp*RhCl₂]₂

The effect of the carboxylate used in a concerted metalation–deprotonation reaction is probed and shows a direct correlation of pKa to observed rate up to a pKa of 4.3, where the rate drops off at higher pKa. The rate of the C–H activation of 2-(4-methoxyphenyl)­pyridine with [Cp*RhCl2]2 and carboxylate follows first-order kinetics in the active metal species, Cp*RhCl­(κ2-OAc), and zero-order kinetics in substrate when in a 1:1 ratio. There is a first-order dependence on substrate observed when excess substrate is present. The evaluation of the mechanism using kinetic studies allowed for a mechanistic proposal in which a second Ph′Py coordinates prior to the rate-determining C–H activation.