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

The reductive capacity of the recently discovered Ln2+ complexes [K­(2.2.2-cryptand)]­[Cp′3Ln], 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′3Y], 1-Y, is capable of reducing naphthalene and forms a mixture of the naphthalenide dianion complex [K­(2.2.2-cryptand)]­[Cp′2Y­(η4-C10H8)], 2-Y, as well as the ligand redistribution product [K­(2.2.2-cryptand)]­[Cp′4Y], 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′2Y­(THF)2]­[BPh4], 5 (synthesized from [Et3NH]­[BPh4] and Cp′3Y), and K/naphthalene. Complex 3-Y was obtained by adding KCp′ to Cp′3Y in the presence of 2.2.2-cryptand. [K­(2.2.2-cryptand)]­[Cp′] was synthesized from 2.2.2-cryptand and KCp′. Each C10 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 (η4-C10H8)2– coordination. In the solid state, 3-Y contains one η1-Cp′ ligand and three η5-Cp′ rings, whereas all four Cp′ rings in 3-La have η5-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 Å from the ring centroid. Complex 1-Y also reduces biphenyl to form [K­(2.2.2-cryptand)]­[Cp′2Y­(η6-C6H5Ph)], 6-Y, which contains a dianion with a planar aromatic phenyl ring as a substituent on a nonplanar η6-C6 ring oriented toward the metal ion.