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. Issue 12 (1st October 2015) - Kotyk, Christopher M.
Abstract : A new option for stabilizing unusual Ln 2+ ions has been identified in the reaction of (C5 H4 SiMe3 )3 Ln (Ln = La, Ce) with potassium graphite and 2.2.2-cryptand in benzene. Abstract : A new option for stabilizing unusual Ln 2+ ions has been identified in the reaction of Cp′3 Ln, 1-Ln (Ln = La, Ce; Cp′ = C5 H4 SiMe3 ), with potassium graphite (KC8 ) in benzene in the presence of 2.2.2-cryptand. This generates [K(2.2.2-cryptand)]2 [(Cp′2 Ln)2 (μ-η 6 :η 6 -C6 H6 )], 2-Ln, complexes that contain La and Ce in the formal +2 oxidation state. These complexes expand the range of coordination environments known for these ions beyond the previously established examples, (Cp′′3 Ln) 1− and (Cp′3 Ln) 1− (Cp′′ = C5 H3 (SiMe3 )2 -1, 3), and generalize the viability of using three anionic carbocyclic rings to stabilize highly reactive Ln 2+ ions. In2-Ln, a non-planar bridging (C6 H6 ) 2− ligand shared between two metals takes the place of a cyclopentadienyl ligand in (Cp′3 Ln) 1− . The intensely colored ( ε = ∼8000 M −1 cm −1 )2-Ln complexes react as four electron reductants with two equiv. of naphthalene to produce two equiv. of the reduced naphthalenide complex, [K(2.2.2-cryptand)][Cp′2 Ln(η 4 -C10 H8 )].