Irradiation of Cp’Ir(PPh3)H2 (Cp’=h5-C5Me5) in benzene resulted in extrusion of dihydrogen, producing hydrido phenyl complex through intermolecular C-H bond activation, and ortho-metalated complex through intramolecular activation. The ratio is 47:53. Reaction pathways were computed by combining density functional theory and coupled cluster methods. The intermolecular reaction starts with the binding of a solvent benzene, forming a π-complex intermediate; which was followed by the oxidative addition of the C-H bond to iridium. In contrast, the corresponding π-complex of the intramolecular pathway has a significantly distorted phenyl ring on triphenylphosphine to lower the energy. Solvent corrected Gibbs free energy barrier between the pre-organized encounter pair and the C-H activation transition state for the intermolecular reaction is ca. 4.5 kcal/mol higher than the intramolecular counterpart, leading to an anticipated rate difference on the order of ca. 103; though the experimental products are almost equal. We infer that the pre-organized complex must be trapped in the intramolecular reaction, thus retards the reaction rate.

Theoretical analysis of C-H activation of Cp’Ir(PPh3)

255th National Meeting (2018)

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