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

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posted on 2015-08-10, 00:00 authored by Jordan F. Corbey, David H. Woen, Chad T. Palumbo, Megan E. Fieser, Joseph W. Ziller, Filipp Furche, William J. Evans
The tris­(cyclopentadienyl) yttrium complexes Cp3Y­(THF), CpMe3Y­(THF), Cp″3Y, Cp″2YCp, and Cp″2YCpMe [Cp = C5H5, CpMe = 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′3Y] and [K­(2.2.2-cryptand)]­[Cp′3Y], 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″2YCp], 2-Y, was characterizable by X-ray crystallography. Reduction of the Cp″3Gd, Cp″2GdCp, and Cp″2GdCpMe 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′3Gd], 1-Gd, were obtained, and [K­(2.2.2-cryptand)]­[Cp″2GdCp], 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 CpIn3Ln (CpIn = C9H7, Ln = Y, Ho, Dy) complexes was the X-ray crystal structure of {K­(2.2.2-cryptand)}2{[(C9H7)2Dy­(μ–η51-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.