The reaction energy profile for the simple model catalyst 1-Mn with a Grubbs-type N-heterocyclic carbene (NHC) moiety is depicted in Figure . The starting point in this olefin metathesis cycle Table : Results of the energy decomposition analysis (EDA) of the model compounds 1-Fe, 1-Mn, 2-Fe and 2-Mn. Dative bonding results from interaction of two singlet fragments, whereas electron-sharing bonding results from triplet-triplet interactions. All energies are given in kcal/mol obtained using TPSSh/TZ2P/D3.