Synthesis and Reduction of Bimetallic Methyl-Bridged Rare-Earth Metal Complexes, [(C5H4SiMe3)2Ln(μ-CH3)]2 (Ln = Y, Tb, Dy)

The complexes [Cp'(2)Ln(mu-CH3)](2), (Cp' = C5H4SiMe3; Ln = Y, Tb, Dy) were reduced to determine if these methyl-bridged complexes would form mixed valent 4f(n)5d(1) Ln(II)/4f(n) Ln(III) compounds or bimetallic 4fn(5)d(1) Ln(II) compounds containing 5d(1)-5d(1) metal-metal bonds upon reduction. Reaction of the known bridged-chloride complexes, [Cp'(2)Ln(mu-Cl)](2), 1-Ln (Ln = Y, Tb, Dy), with MeLi forms the bridged-methyl complexes [Cp'(2)Ln(mu-CH3)](2), 2-Ln, which were crystallographically characterized for Tb and Dy. KC8 reduction of 2-Ln in the presence of 2.2.2-cryptand produced 3-Y, 3-Tb, and 3-Dy, which exhibited intense dark colors and broad absorbance peaks around 400 nm with molar extinction coefficients of 1700, 2300, and 1800 M-1 cm(-1), respectively, which are characteristics of Ln(II) ions. The dark maroon 3-Y product had an axial electron paramagnetic resonance spectrum at 77 K (g(1) = 1.99, A(1) = 17.9 G; g(2) = 2.00, A(2) = 17.7 G) and a two-line isotropic spectrum at 273 K (g = 1.99, A = 18.4 G), which indicates that an Y(II) ion is present. Although these results are indicative of Ln(II) ions present in the solution, crystallographic evidence was not obtained to establish the structure of these complexes.