In order to circumvent this problem and at the same time maintain the 6-fold coordination, bidentate ligands can be used. In this respect, 8-Mn represents an octahedral modification and extension of 1-Mn. In contrast to tridentate ligands, bidentate ligands can offer more structural flexibility and are less rigid. Experimentally, a compound such as 8-Mn could be derived from a carbonyl precursor [Mn(NHC-P)(CO) 3 R] (R = Alkyl, Aryl, OAc) or a putative dinuclear precatalyst. To further increase the donor strength of the ligand, a bis-NHC system could be employed, which is also well established in literature. The reaction energy profile for an olefin metathesis cycle with the octahedral species 8-Mn is shown in Figure . For simplicity reasons, again only one isomer was considered in the following and the starting point is the coordinated olefin adduct. The energetic barrier for the initial [2+2]cycloaddition of the simple test substrate ethylene is low (∆G ‡ = 3.5 kcal/mol) and quickly leads to formation of a stable singlet metallacycle. In the absence of surface crossings and isomerisation reactions, the most important side reaction is cyclopropanation and formation of methylcyclopropane. The barrier for this process was calculated to be 22.4 kcal/mol in the singlet state.