The first prepared and well-characterized f-block metallocenes were the tris(cyclopentadienyl) lanthanide complexes, (C5H5)3Ln (Ln = La, Ce, Pr, Nd, Sm and Gd).
Subsequently, William J. Evans and his coworkers successfully isolated (C5Me5)2Sm(THF)2[8] and (C5Me5)2Sm,[9] making a breakthrough in f-block metallocenes, since both of these two organosamarium(II) complexes were unexpectedly found to participate in the coordination, activation and transformation of a variety of unsaturated compounds, including olefins,[8][10][11][12] dinitrogen,[13] internal alkynens,[14][15] phosphaalkynes,[16] carbon monoxide,[17] carbon dioxide,[18] isonitriles,[19] diazine derivatives,[20][21][22] imines[23] and polycyclic aromatic hydrocarbons (PAHs).
Generally, in order to synthesize (C5Me5)3M, the starting materials and the reaction conditions require optimizing to ensure (C5Me5)3M is the most favored product.
[35] The following complexes, (C5H4SiMe3)3Ln, have extremely negative reduction potentials of -2.7 to -3.9 Volts versus the standard hydrogen electrode (NHE).
[36] Furthermore, in comparison with d-orbitals of transition metals, the radial extension of their 4f-orbitals are really small and limited, which greatly reduces the orbital effects.
[37] More specifically, its 4fn electron configurations have almost no effect on its chemical reactivity and its electrostatic interactions require optimizing through ligand geometries.
Like alkyl group, the electron-rich ligand of f-block metallocenes can act as a nucleophile during organometallic reactions.
The f-block metallocenes are able to undergo insertion reactions of compounds like carbon monoxide,[41] nitriles or isocyanates.
[42] Due to the strong steric hindrance, one ligand cannot bind to the metal center at the ideal distance and so the complex is not stable.