In order to gain a better understanding of the M=CH 2 (M = Fe, Mn) bonds in our singlet model systems, we first carried out energy decomposition analysis (EDA-NOCV) as applied and advocated by Frenking and coworkers. The EDA decomposes the interaction energy ∆E int between two fragments within a molecule into three different components, namely ∆E elstat , ∆E Pauli and ∆E orb , in order to obtain a chemically meaningful bonding picture. Thereby, either two closedshell fragments that interact or two triplet fragments that interact in an anti-parallel fashion can be generated in the EDA. Whichever fragmentation yields values closer to zero for the orbital mixing term ∆E orb determines the chemical interpretation of the bonding. If the two singlet fragments yield a lower value, the bond is termed dative, whereas if it is the two anti-parallel triplet fragments, the bonding is referred to as electron sharing. Metal carbene complexes with an electron-sharing bonding are traditionally classified as Schrock-type (alkylidene), while those with a dative bonding as Fischer-type. Table shows a compilation of the energy values obtained by decomposition analysis with TPSSh/TZ2P/D3. Complex 1-Fe can be described as electron-sharing bearing two interacting triplet fragments, while the carbene bond in 1-Mn can rather be described with a dative interaction. However, the differences for the decisive ∆E orb values in the manganese and iron systems are small. To further investigate the nature of the M=CH 2 bond, Wiberg bond orders were calculated to be 1.70 in the Fe and 1.91 in the Mn complex, respectively. This analysis points to a more pronounced double bond character in the Mn system. According to EDA, the model catalysts 2-Fe and 2-Mn can both be described as having two interacting triplet fragments and can therefore be classified as Schrock-type carbenes. The associated bond order is 2.11 for the Fe system and 2.19 for the Mn system, respectively. Consequently the double bond character in these complexes is more pronounced than in 1-Fe and 1-Mn. In all cases investigated, the total interaction energy ∆E int of the closed-shell fragments was much lower (negative) than that of the triplet fragments. Based on this limited data set, no clear differentiation of Fe vs. Mn carbene complexes can be made. Within one pair of complexes Fe and Mn behave rather similar, while the differences attributed to the different ligand spheres are more pronounced between the two pairs, 1-Fe/1-Mn vs. 2-Fe/2Mn. A comparison with related Ru based carbene species, namely 2-Ru, the analogous structure to 2-Mn and a second generation Grubbs catalyst, revealed that these also favor an electron-sharing bonding mode. At least within the EDA, the carbenes can be considered as similar -highlighting once more the diagonal relationship of Ru and Mn. Details about these calculations can be found in the Supporting Information (see table ).