Ln(II)/Pb(II)–Ln(III)/Pb(0) Redox Approach toward Rare-Earth-Metal Half-Sandwich Complexes

The divalent bis­(trimethylsilyl)­amide
complexes Ln­[N­(SiMe3)2]2(THF)2 (Ln = Sm, Yb) react with
0.5 equiv of lead­(II) pentamethylcyclopentadienide, Cp*2Pb (Cp* = C5Me5), in n-hexane
to form the half-sandwich complexes Cp*Ln­[N­(SiMe3)2]2 (Ln = Sm, Yb) in almost quantitative yield.
The same reaction performed with Eu­[N­(SiMe3)2]2(THF)2 resulted in the cocrystallization
of the sandwich complex Cp*2Eu­[N­(SiMe3)2] and homoleptic Eu­[N­(SiMe3)2]3. The divalent bis­(dimethylsilyl)­amide complexes Ln­{[μ-N­(SiHMe2)2]2Ln­[N­(SiHMe2)2]­(THF)}2 (Ln = Sm, Yb) react with 1.5 equiv of Cp*2Pb in n-hexane/THF to form the half-sandwich
complexes Cp*Ln­[N­(SiHMe2)2]2(THF)
(Ln = Sm, Yb). The corresponding europium reaction did not provide
any crystalline material. Treatment of divalent Eu­[N­(SiMe3)2]2(THF)2 with 2 equiv of 3-tert-butyl-5-methylpyrazole (HpztBu,Me) in THF generates [(pztBu,Me)­Eu­(μ-pztBu,Me)­(THF)2]2. Oxidation
of the europium­(II) pyrazolate complex with 1 equiv of Cp*2Pb in THF afforded Cp*Eu­(μ-pztBu,Me)2(THF)2. The tetramethylaluminate compounds
{Ln­(AlMe4)2}n (Ln
= Sm, Yb) react with 0.5 equiv of PbCp*2 in n-hexane to produce mixtures of half-sandwich and metallocene complexes
Cp*Ln­(AlMe4)2 and [Cp*2Ln­(μ-AlMe4)]2, respectively. The attempted oxidation of {Eu­(AlMe4)2}n led to the formation
of {Cp*Eu­(AlMe4)}, which could be crystallized from THF
to give polymeric {Cp*Eu­(μ-AlMe4)­(THF)3}n. The reaction of “chloro-contaminated”
{Sm­(AlMe4)2}n with
2 equiv of HCp* performed in THF led to the isolation of the unexpected
mixed chloride methylidene complex [Cp*3Sm3(μ2-Cl)3(μ3-Cl)­(μ3-CH2)­(THF)3]. Reacting {Yb­(AlEt4)2}n with 0.5 equiv of Cp*2Pb in n-hexane gave a mixture of products,
from which Cp*2Yb­(AlEt4) was identified. Performing
the same reaction in toluene in the presence of diethyl ether resulted
in the formation of the divalent metathesis product Cp*Yb­(AlEt4)­(Et2O)2.