Trimethylsilyl versus Bis(trimethylsilyl) Substitution in Tris(cyclopentadienyl) Complexes of La, Ce, and Pr: Comparison of Structure, Magnetic Properties, and Reactivity

To evaluate the effect of cyclopentadienyl ligand substitution in complexes of new +2 ions of the lanthanides, comparisons in reactivity and spectroscopic and magnetic properties have been made between [K(crypt)][Cp′3Ln], 1-Ln (Cp′ = C5H4SiMe3; crypt = 2.2.2-cryptand; Ln = La, Ce, Pr, and Nd), and [K(crypt)][Cp′′3Ln], 2-Ln [Cp′′ = C5H3(SiMe3)2]. The 2-Ln complexes (Ce, Pr, and Nd) were synthesized by reduction of Cp′′3Ln with potassium graphite in the presence of crypt and crystallographically characterized. The structures and UV–visible spectra of 2-Ln are similar to those of 1-Ln, as expected, but greater thermal stability for 2-Ln, expected from comparisons of 2-U and 1-U, was not observed. The magnetic susceptibilities of 2-Ce and 2-Pr were investigated because those of 1-Ce and 1-Pr did not match simple coupling models for 4fn5d1 electron configurations. The magnetic data of the 2-Ln complexes are similar to those of 1-Ln, which suggests that Ce2+ and Pr2+ complexes with 4fn5d1 electron configuration...