We could localize a MECP at ∆G MECP ≈ 2.3 kcal/mol above the singlet state, low enough to allow thermal deactivation of the catalyst by surface crossing. Similarly, for the PCP complex 2-Mn (see metallacycle in Figure ) a MECP could be localized at ∆G MECP ≈ 2.8 kcal/mol above the singlet state. These surface crossing points are well-accessible at reaction conditions and can compete with all other reaction steps.