 At 30 °C, the 1H NMR spectrum shows only two peaks, one typical (δ5.6) of the η5-C5"H"5 and the other assigned η1-C5"H"5.The singlet assigned to the η1-C5H5 ligand splits at low temperatures owing to the slow hopping of the Fe center from carbon to carbon in the η1-C5H5 ligand.Two mechanisms have been proposed, with the consensus favoring the 1,2 shift pathway.