Reactivity of the Ln2+ Complexes [K(2.2.2-cryptand)][(C5H4SiMe3)3Ln]: Reduction of Naphthalene and Biphenyl

The reductive capacity of the recently discovered Ln(2+) complexes [K(2.2.2-cryptand)][Cp'(3)Ln], 1-Ln (Cp' = C5H4SiMe3; Ln = Y, La, Ce, Dy), has been probed by examining their reactions with aromatic hydrocarbons. [K(2.2.2-cryptand)][Cp'Y-3], 1-Y, is capable of reducing naphthalene and forms a mixture of the naphthalenide dianion complex [K(2.2.2-cryptand)][Cp'Y-2(eta(4)-C10H8)], 2-Y, as well as the ligand redistribution product [K(2.2.2-cryptand)][Cp'Y-4], 3-Y, and the cyclopentadienyl ligand salt [K(2.2.2-cryptand)][Cp'], 4. Naphthalene is reduced analogously by 1-La, 1-Ce, and 1-Dy. Each complex in the yttrium reaction was synthesized independently to confirm its identity in the mixture. Complex 2-Y was prepared from [Cp'Y-2(THF)(2)][BPh4], 5 (synthesized from [Et3NH][BPh4] and Cp'Y-3), and K/naphthalene. Complex 3-Y was obtained by adding KCp' to Cp'Y-3 in the presence of 2.2.2-cryptand. [K(2.2.2-cryptand)][Cp'] was synthesized from 2.2.2-cryptand and KCp'. Each C-10 unit in the reduced naphthalene products, 2-Y, 2-La, 2-Ce, and 2-Dy, is bent with four carbon atoms of one ring oriented toward the metal, while the remaining six carbon atoms form a planar ring consistent with (eta(4)-C10H8)(2) coordination. In the solid state, 3-Y contains one eta(1)-Cp' ligand and three eta(5)-Cp' rings, whereas all four Cp' rings in 3-La have eta(5)-coordination. In the solid-state structure of 4, the (Cp')- anion is not coordinated to potassium, which is encapsulated by the cryptand and located 7.063 angstrom from the ring centroid. Complex 1-Y also reduces biphenyl to form [K(2.2.2-cryptand)][Cp'2Y(eta(6)-C6H5Ph)], 6-Y, which contains a dianion with a planar aromatic phenyl ring as a substituent on a nonplanar eta(6)-C-6 ring oriented toward the metal ion.