Investigations into the reactivity of a molybdenocene formamidinate complex

• A molybdenocene amidinate complex yields an unstable carbene upon deprotonation. • N-heterocyclic carbenes add to the η 5 -Cp ring of the cationic amidinate complex. • The resulting η 4 -cyclopentadiene complex shows dynamic behaviour. A cationic molybdenocene amidinate complex was investigated in view of its suitability to serve as a precursor for a metalla-N-heterocyclic carbene. Upon deprotonation, an amidinate complex with a cyclopenatdiene substituent at the amidinate C atom was identified. This points to the intermediate formation of the sought-after carbene which nucleophilicly attacks a Cp ring of the remaining cationic molybdenocene precursor and subsequent fragmentation. In contrast, the nucleophilic attack of standard imidazolylidenes to the cationic molybdenocene amidinate yields stable adducts with a η 4 -cyclopentadiene ligand. The rotational dynamics of this structure has been studied by variable temperature NMR studies. The experimental findings are supported by DFT calculations.