Subsequently, we focused on the mechanism accounting for 1-hexene isomerization after formation of [Ir(POCOP)(1-hexene)] + (A.1 in Figure ). Strikingly, our results revealed that a virtually identical mechanism to that proposed for Ir I through an Ir I /Ir III redox cycle was also feasible for an exotic open-shell Ir II /Ir IV pair, but proceeding with a significantly lower activation energy (Figure ). The reaction mechanism involves the same elementary steps for the closed and open-shell systems, namely C-H bond oxidative addition (A.2 in Figure ), η 3 -allyl/η 1 -allyl ligand rearrangement (A.3) and reductive elimination to produce the internal olefin (A.4). The catalyst is recovered by the barrierless release of 2-hexene. The only differences found were the existence of two additional minima accounting for rotational steps during ligand rearrangement and reductive elimination in the Ir I system (see Figure ), which do not affect the overall catalytic cycle but showcase a reduction of the required steps for the Ir II /Ir IV couple. Notably, although the elementary steps are shared, the rate-limiting one differs for the two systems. While for the traditional Ir I /Ir III couple the rate of reaction is determined by either oxidative addition or reductive elimination, for which the respective overall barriers of 28.0 and 29.9 kcal/mol are within 2 kcal/mol, the rate-limiting step for the Ir II /Ir IV pair lies at a considerably lower value of 21.8 kcal/mol and corresponds to the η 3 -to-η 1 allyl ligand rearrangement. To further gauge the proposed mechanism, we conducted kinetic experiments. We monitored the isomerization of 1-hexene by 1 H NMR at 70 °C mediated by 1•BAr F (1 mol%), revealing a firstorder dependence for olefin concentration (Figure and section 5 of SI). The average experimentally determined ΔG ‡ at 70 °C was 22.4 kcal/mol, with a corresponding pseudo-first order kinetic constant of 0.05 s -1 and turnover frequency of 0.02 s -1 . The Eyring analysis of the temperature dependence of the reaction rate constants gave an enthalpy of activation (ΔH ‡ ) of 20.8 kcal/mol, whereas the entropy of activation (ΔS ‡ ) was -2.8 cal/(mol•K). This latter result of a close-to-zero activation entropy is compatible with a rate-limiting step involving an allyl/vinyl rearrangement and certainly supports that neither a dissociation nor an association process is implied, in agreement with our prior calculations (Figure ). Besides, the Energy Span model, performed by means of the AUTOF program, ( ) provides a turnover frequency of 6.6•10 -3 s -1 which is in reasonable agreement with our experimental findings. Considering the uniqueness of the investigated Ir II /Ir IV redox cycle, we aimed to better understand the factors contributing to its superior performance compared to the conventional Ir I /Ir III pair. To this end, we applied the Activation Strain Model (ASM) of reactivity to the initial C-H bond oxidate addition step for both Ir I and Ir II -mediated reactions. This analysis decomposes the electronic energy (ΔE) into two terms, namely the strain (ΔE strain ) that results from the distortion of the individual reactants and the interaction (ΔE int ) between the deformed reactants along the reaction coordinate, defined in this case by the C•••H bond-breaking distance. As this particular transformation occurs intramolecularly, the fragments, i.e., the alkene ligand and the Ir(POCOP) moiety, were referred to the geometry they adopt in the initial intermediate A.1/B.1 complexes, constituting therefore the zero level of the different ASM terms. Figure shows the corresponding activation strain diagrams (ASDs) computed for both reactions at the proximities of the corresponding transition states (TS1). From the data in Figure , it becomes clear that the lower barrier computed for the Ir II -mediated reaction does not derive from the strain energy (E strain ), which is nearly identical for both processes, but exclusively from a stronger interaction (E int ) between the deformed fragments along the entire reaction coordinate. Reasons behind the stronger interaction energy computed for the Ir II -reaction can be further analyzed by means of the Energy Decomposition Analysis (EDA), which involves decomposing the E int into the following chemically meaningful terms: classical electrostatic interaction (E elstat ), Pauli repulsion between closed-shell orbitals (E Pauli ), responsible for steric repulsion, stabilizing orbital attractions (E orb ) and dispersion interactions (E disp ). From the data in Figure , which graphically shows the evolution of the EDA contributors along the reaction coordinate and referred again to the initial intermediate, it becomes clear that the enhanced interaction in the Ir II -reaction results from more stabilizing orbital interactions and electrostatic (albeit to a lesser extent) attractions, which compensate the less stabilizing Pauli repulsion compared with the process involving the Ir I -complex. Whereas the stronger E elstat term is easily understandable as the [Ir(POCOP)] fragment in the Ir II system presents a net positive charge, reasons for the enhanced orbital interactions for the Ir II system are two-fold: i) the higher oxidation state of the metal fosters increased ligand-to-metal donation as confirmed by the larger overlap between lower in energy iridium orbitals and ligand orbitals; and ii) the SOMO can engage not only in accepting interactions from the olefin fragment, but also in backdonation. Indeed, for the Ir II -system, besides the donation from the -HOMO of the olefin fragment into the SOMO of the [Ir(POCOP)] fragment, an additional donation from the Ir-centered SOMO to the *-LUMO of the olefin is present, which is of course absent in its Ir I -counterpart (Fig. ). Finally, we also analyzed the somewhat counterintuitive higher Pauli repulsion computed for the Ir II -reaction. Our calculations indicate that this is mainly due to a significantly higher overlap between the doubly-occupied d atomic orbital of the transition metal (HOMO-1) and the -HOMO of the alkene as compared to the similar four-electron interaction in the Ir I -system (Table In summary, our ASM-EDA analyses indicate that the enhanced reactivity of the Ir II -system in the key initial C-H bond oxidative addition results exclusively from a stronger interaction between the transition metal fragment and the alkene ligand which derives from more stabilizing orbital and electrostatic (albeit to a lesser extent) interactions, which compensate for a less favorable Pauli repulsion.