Synthesis and reactivity of cationic lanthanide metallocene complexes. Hexabromocarborane and tetraphenylborate as counter ions

Abstract

Treatment of unsolvated Cp″₂Ln(II) [Cp″ = 1,3-(Me₃Si)₂C₅H₃] with 1 equivalent of Ag(I)Y, or reaction of [Cp″₂LnI]₂ with 2 molar equivalents of Ag(CB₁₁Br₆H₆) in pure toluene at room temperature gave “Lewis base-free” cationic lanthanide metallocene complexes [Cp″₂Ln]Y (Y = BPh₄^–, Ln = Sm 1, Yb 2; Y = CB₁₁Br₆H₆^–, Ln = Sm 3, Er 4) in good yield. They slowly undergo decomposition reaction at room temperature. The reactivity of these “Lewis base-free” cationic complexes is highly dependent upon the coordinating nature of the counter ions. Complexes 3 and 4 are much more reactive than 1 and 2. Recrystallization of 1 and 2 from 1,2-dimethoxyethane (DME) and THF yielded [Cp″₂Sm(DME)][BPh₄] 5 and [Cp″₂Yb(THF)₂][BPh₄] 6, respectively. However, recrystallization of 3 and 4 from THF resulted in the ring-opening polymerization of THF. The THF coordinated complexes [Cp″₂Ln(THF)₂][CB₁₁Br₆H₆] (Ln = Sm 7, Er 8) were isolated via recrystallization of 3 and 4 from toluene containing a small amount of THF. The “Lewis base-free” cation “Cp″₂Er⁺” can abstract one bromine atom from the counter ion CB₁₁Br₆H₆^– or one chlorine atom from CH₂Cl₂ to form [Cp″₂ErBr]₂ or [Cp″₂ErCl]₂, respectively. Unfortunately, these cations do not exhibit reactivity towards 1-hexene at room temperature. Molecular structures of 5, 7, 8 and [Cp″₂ErBr]₂ have been confirmed by single-crystal X-ray analyses.