Recent results in reductive rare-earth metal chemistry have shown that complexes with the metal in the +2 oxidation state can be isolated for yttrium and all the rare-earth metals (except radioactive Pm) in tris(silylcyclopentadienyl) ligand environments, (Cp'3Ln)1− and (Cp''3Ln)1− [Cp' = (C5H4SiMe3)1−; Cp'' = (C5H3(SiMe3)2-1,3)1−]. Spectroscopic, structural, and theoretical investigations revealed that these new Ln(II) ions adopted 4fn5d1 ground state electron configurations instead of the expected 4fn+1 ground state usually obtained by reduction of a 4fn Ln(III) complex. The isolation of 4fn5d1 lanthanide ions raises the possibility that bimetallic complexes could have a Ln–Ln bond via the 5d electrons. These targets have been explored by reduction of bimetallic hydride complexes. Yttrium was examined first since Y(III) is diamagnetic and the 100% naturally abundant I = ½ 89Y nucleus aids in the EPR identification of Y(II). The reductive chemistry of [Cp'2Ln(μ–H)(THF)]2 (Ln = Y, Dy, Tb) was examined to determine if these hydrides would be viable precursors for 4f n5d1 Ln2+ complexes containing 5d1-5d1 metal–metal bonds. Reductions of [Cp'2Ln(μ–H)(THF)]2 with KC8 in the presence of 2.2.2-cryptand (crypt) or 18-crown-6 gave reaction products with intense dark colors characteristic of Ln2+ ions. The dark green yttrium product gave a rhombic EPR spectrum at 298 K. However, the only crystallographically-characterizable products obtainable from these solutions were Ln3+ polyhydride anion complexes of composition, [K(chelate)]{[Cp'2Ln(μ–H)]3(μ–H)}. Subsequently, the ansa-metallocene ligand [Me2Si(C5H3-3-Me3Si)2] (CpAn) was explored. [CpAnY(μ–H)(THF)]2 was synthesized and crystallographically characterized. Reduction with KC8 in the presence of 2.2.2-cryptand yielded the mixed valent yttrium complex [K(crypt)][CpAnY(μ–H)]2 which was also characterized by X-ray crystallography. The two structures will be described as well as efforts to obtain analogs with other rare earth ions.

Exploring the synthesis and reductive chemistry of bimetallic rare-earth complexes

256th National Meeting (2018)

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