Analysis of the 1 H NMR spectrum of 2 in toluene-d8 revealed only very broad resonances at room temperature, possibly resulting from a fluxional behavior of the Cp ttt ligands. A better resolved spectrum featuring three broad resonances at d ≈ 171, 32 and 2 ppm was obtained upon recording the spectrum at 80 °C (see Figures ), and is consistent with free rotation of the Cp ttt ligands leading to an overall D2h symmetric species in solution at high temperature. In the IR spectrum of 2, no significant absorption band was observed in the range 1500-2800 cm -1 , all the more so in the expected region for C≡C triple bonds, which can be explained by the IR selection rules (lack of change in the molecular dipole).