The reductive capacity of the recently discovered Ln 2+ complexes [K(2.2.2-cryptand)][Cp′ 3 Ln], 1-Ln (Cp′ = C 5 H 4 SiMe 3 ; Ln = Y, La, Ce, Dy), has been probed by examining their reactions with aromatic hydrocarbons. [K-(2.2.2-cryptand)][Cp′ 3 Y], 1-Y, is capable of reducing naphthalene and forms a mixture of the naphthalenide dianion complex [K(2.2.2-cryptand)][Cp′ 2 Y(η 4 -C 10 H 8 )], 2-Y, as well as the ligand redistribution product [K(2.2.2-cryptand)][Cp′ 4 Y], 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′ 2 Y(THF) 2 ]-[BPh 4 ], 5 (synthesized from [Et 3 NH][BPh 4 ] and Cp′ 3 Y), and K/naphthalene. Complex 3-Y was obtained by adding KCp′ to Cp′ 3 Y 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 (η 4 -C 10 H 8 ) 2− coordination. In the solid state, 3-Y contains one η 1 -Cp′ ligand and three η 5 -Cp′ rings, whereas all four Cp′ rings in 3-La have η 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 Å from the ring centroid. Complex 1-Y also reduces biphenyl to form [K(2.2.2-cryptand)][Cp′ 2 Y(η 6 -C 6 H 5 Ph)], 6-Y, which contains a dianion with a planar aromatic phenyl ring as a substituent on a nonplanar η 6 -C 6 ring oriented toward the metal ion. ■ INTRODUCTIONRecently, the number of +2 ions available in the lanthanide series in soluble molecular complexes has been expanded from the traditional list of six, namely, Eu 2+ , Yb 2+ , Sm 2+ , Tm 2+ , Dy 2+ , and Nd 2+ , to the rest of the lanthanides except radioactive promethium via the potassium graphite reactions shown in Schemes 1 1 and 2. 2−4 The availability of these complexes allows the reaction chemistry of these new oxidation states to be investigated for the first time.A traditional way to characterize reducing agents too reactive for reproducible electrochemistry is to treat them with polycyclic hydrocarbons of known reduction potential. 5−8 This was initially used to characterize the reactivity 5 of (C 5 Me 5 ) 2 Sm 9 and subsequently used for NdI 2 6 and DyI 2 . 7 (C 5 Me 5 ) 2 Sm can reduce anthracene (−1.98 V vs SCE 10 ) to form [(C 5 Me 5 ) 2 Sm] 2 (μ-C 14 H 10 ), but it does not reduce naphthalene (−2.60 V vs SCE 10 ). 5 The stronger reductants, NdI 2 and DyI 2 , reduce naphthalene in 1,2-dimethoxyethane (DME) and THF to produce [NdI 2 (THF) 3 ] 2 (μ-C 10 H 8 ) 6 and (C 10 H 8 )DyI(DME) 2 , 7 respectively. Although other reduced naphthalene complexes of the rare earth ions are known, 8,11−18 their preparations involve either (a) initial...

A new option for stabilizing unusual Ln2+ ions has been identified in the reaction of (C5H4SiMe3)3Ln (Ln = La, Ce) with potassium graphite and 2.2.2-cryptand in benzene.