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.