Computational Analysis of Two-State Reactivity in β‑Hydride Elimination Mechanisms of Fe(II)– and Co(II)–Alkyl Complexes Supported by β‑Diketiminate Ligand

β-Hydride elimination in Fe­(II)– and Co­(II)–alkyl complexes is known to occur through two different spin multiplicity states and is thus a good example of two-state reactivity. In this study, the automated reaction path search method combined with the mixed-spin effective Hamiltonian approach has been applied to understand the detailed reaction mechanisms including the characterization of the spin-inversion points between the high-spin and low-spin potential energy surfaces for the Fe­(II)–C2H5 and Co­(II)–C2H5 complexes supported by a β-diketiminate ligand. Density functional theory (DFT) with different exchange-correlation functionals has been used in the reaction path search calculations. We found that the β-hydride elimination process for these complexes consists of multiple steps including two spin-inversion points. We have also investigated the substituent effect in the β-diketiminate ligand to understand the steric and electronic effects on the spin-inversion process. The efficiency of the spin-inversion process has been discussed in terms of the calculated spin–orbit couplings between the high- and low-spin states.