Ligand Effects in the Synthesis of Ln2+ Complexes by Reduction of Tris(cyclopentadienyl) Precursors Including C-H Bond Activation of an Indenyl Anion

The tris(cydopentadienyl) yttrium complexes Cp3Y(THF), (Cp3Y)-Y-Me(THF), Cp-3 '' Y, Cp-2 '' YCp, and Cp-2 '' YCpMe [Cp = C5H5, Cp-Me = C5H4Me, Cp '' = C5H3(SiMe3)(2)] have been treated with potassium graphite in the presence of 2.2.2-cryptand to search for more stable examples of complexes featuring the recently discovered Y2+ ion first isolated in [K(18-crown-6)][Cp-3'Y] and [K(2.2.2-cryptand)][Cp-3'Y], 1-Y (Cp' = C5H4SiMe3). Reduction of the tris(cyclopentadienyl) complexes generates dark solutions like that of 1-Y, and the EPR spectra contain doublets with g values between 1.990 and 1.991 and hyperfine coupling constants of 34-47 gauss that are consistent with the presence of Y2+. [K(2.2.2-cryptand)][Cp-2 '' YCp], 2-Y, was characterizable by X-ray crystallography. Reduction of the Cp-3 '' Gd, Cp-2 '' GdCp, and Cp-2 '' GdCpMe complexes containing the larger metal gadolinium were also examined. In each case, dark solutions and EPR spectra like that of [K(2.2.2-cryptand)][Cp-3'Gd], 1-Gd, were obtained, and [K(2.2.2-cryptand)][Cp-2 '' GdCp], 2-Gd, was crystallographically characterizable. None of the new yttrium and gadolinium complexes displayed greater stability than 1-Y and 1-Gd. Exploration of this reduction chemistry with indenyl ligands did not give evidence for +2 complexes. The only definitive information obtained from reductions of the Cp(3)(In)Ln (Cp-In = C9H7, Ln = Y, Ho, Dy) complexes was the X-ray crystal structure of {K(2.2.2-cryptand)}(2){[(C9H7)(2)Dy(mu-eta(5):eta(1)-C9H6)](2)}, a complex containing the first example of the indenyl dianion, (C9H6)(2-), derived from C-H bond activation of the (C9H7)(1-) monoanion. Density functional theory analysis of these results provides an explanation for the observed hyperfine coupling constants in the yttrium complexes and for the C-H bond activation observed for the indenyl complex.