Reversible Concerted Metalation-Deprotonation C-H Bond Activation by [Cp*RhCl2]2.

The reversibility of the concerted metalation-deprotonation exchange of eight para-substituted phenylpyridines is examined with the parent Cp*RhCl(κ-C,N-NC5H4-C6H4). Equilibrium constants are determined, and the free energies are used to extract the most important parameters that control the thermodynamics. Keq values are found to correlate best with heterolytic C-H bond strengths but in a way that is not obvious considering the electrophilic nature of these activations.