Lanthanide(III)/Actinide(III) Differentiation in Mixed Cyclopentadienyl/Dithiolene Compounds from X-ray Diffraction and Density Functional Theory Analysis

Treatment of [U(Cp*)2Cl2] with Na2dddt in thf afforded the “ate” complex [U(Cp*)2Cl(dddt)Na(thf)2] (1), and the salt-free compound [U(Cp*)2(dddt)] (2) could be extracted from 1 with toluene (Cp* = η-C5Me5; dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate). Reduction of 2 with Na(Hg) or addition of Na2dddt to [U(Cp*)2Cl2Na(thf)x] in the presence of 18-crown-6 gave the first uranium(III) dithiolene compound, [Na(18-crown-6)(thf)2][U(Cp*)2(dddt)] (4). The dimeric lanthanide complexes [{Ln(Cp*)2(dddt)K(thf)2}2] (Ln = Ce (5), Nd (6)) were prepared by reaction of [Ln(Cp*)2Cl2K] with K2dddt, and in the presence of 15-crown-5, they were transformed into the cation−anion pairs [K(15-crown-5)2][Ln(Cp*)2(dddt)] (Ln = Ce (7), Nd (8)). The crystal structures of 2, 4·thf, 5−7, 7·0.5(pentane), and 8·0.5(pentane) were determined by X-ray diffraction analysis. Comparison of the structural parameters of the anions [M(Cp*)2(dddt)]- (M = U, Ce, Nd) revealed that the U−S and U−C(Cp*) distances are shorter than those expected fro...