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

Abstract

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...

Expanding the Chemistry of Molecular U2+ Complexes: Synthesis, Characterization, and Reactivity of the {[C5H3(SiMe3)2]3U}− Anion

“…,b otho fw hich were identified by X-ray crystallographya nd NMR spectroscopy [15] [see Equation (6), Figure 5]. T his result contrasts with the reactiono fC p ' 3 Uw ith C 8 H 8 which forms Cp' 2 U(C 8 H 8 ).…”

“…[20] The only crystallographically characterized tetrakis(cyclopentadienyl) U 4 + complex is Cp 4 U. [21] An yttrium analogue of 4 is known [15] that is not isomorphous but has the same coordination environmentc ontaining three h [15] The 2.56(2) U -(h 5 -Cp' ring centroid) averaged istance and the 2.776(2) U -C25(h 1 -Cp')d istance in 4 are numericallyl arger than those in the yttrium complex, 2.48(1) and 2.680(2) , [15] respectively,w hichi sc onsistentw ith the larger ionic radius of U 3 + versus Y 3 + (1.025 v s0 .900 , respectively, using the Shannonr adii available only for six coordinate species). [22] Independent syntheses of…”

Isolation of +2 rare earth metal ions with three anionic carbocyclic rings: bimetallic bis(cyclopentadienyl) reduced arene complexes of La2+ and Ce2+ are four electron reductants

“…of [K(2.2.2-cryptand)][Cp′ 2 Ln(η 4 -C 10 H 8 )], 4-Ln (Ln = La, Ce), Scheme 5 . 37 The four electron reduction is consistent with the presence of two Ln 2+ ions and a (C 6 H 6 ) 2– dianion, but does not provide definitive evidence on this because a (C 6 H 6 ) 4– anion would also be a 4-electron reductant. This reaction does provide a clean route to 4-Ln , which are originally made from 3-Ln in a reaction that has an inseparable byproduct, [K(2.2.2-cryptand)][Cp′ 4 Ln] (Ln = Y, La) that required 4-La to be separated a la Pasteur .…”

“…This reaction does provide a clean route to 4-Ln , which are originally made from 3-Ln in a reaction that has an inseparable byproduct, [K(2.2.2-cryptand)][Cp′ 4 Ln] (Ln = Y, La) that required 4-La to be separated a la Pasteur . 37 …”

Evaluating Electron‐Transfer Reactivity of Complexes of Actinides in +2 and +3 Oxidation States by using EPR Spectroscopy

“…[11][12][13][14][15][16][17][18][19] When an ew oxidation state is identified, one of the characteristics to be defined is the redox potential by which it is formed. [23][24][25] Sincet he recently discovered + 2i ons can all be generated by reduction using alkali metals, it appearst he reduction potentials are less negative than the À2.86 Vv s. Fc + /Fc, the potential of Na. [20][21][22] Frequently,c hemical analysiso fr eductive capacity is made by examining reactions of polycyclic aromatic hydrocarbonso fk nown reduction potential.…”