Cation size dependent reactivity of lanthanide trihalides with bulky alkylcyclopentadienyl anions

Abstract

Reactions of NdCl₃ and PrCl₃ with two equivalents of sodium tri-tert-butylcyclopentadienide furnished base- and salt-free [Cp′₂NdCl] and [Cp′₂PrCl] (Cp′ = 1,2,4-(Me₃C)₃C₅H₂) in good yield. Trimethylaluminium has been added to the neodymium complex to form [Cp′₂NdClAlMe₃]. With LaCl₃ or CeCl₃ base-free bis(ring) complexes were not obtained, but in the latter case the salt adduct [(⁴Cp₂Ce)(μ-Cl)₂Na(tmeda)₂]_∞ (⁴Cp = (Me₂CH)₄C₅H) could be extracted from the product mixture with tetramethylethylenediamine and crystallized as a zigzag chain polymer. [⁴Cp₂SmCl₂Na(dme)₂] retained the coordinated sodium chloride even when dissolved in non-polar solvents. Attempted preparation of [Cp′₂YbCl] gave the mono(ring) complex [Cp′YbCl(μ-OCH₂CH₂OCH₃)]₂ from cleavage of the dimethoxyethane solvent and with lutetium trichloride the hexanuclear complex [(⁴CpLu)₅LuCl₁₃(OEt₂)₅] was prepared in low yield. For lanthanum and thulium use of the triiodide as a starting compound enabled synthesis of the corresponding bis(tetraisopropylcyclopentadienyl)metal iodide, bis{tri-tert-butylcyclopentadienyl}lanthanum iodide was also prepared from LnI₃. [⁴Cp₂TmI] shows a unique conformation of one of the tetraisopropylcyclopentadienyl ligands with two isopropyl neighbours rotated towards each other indicating extreme steric congestion. Oxidation of [Cp′₂Sm] with copper(I) iodide gave [Cp′₂SmI] in high yield. Mono(ring) complexes are readily available from trichlorides of thulium, ytterbium, and lutetium. Apart from the donor solvent adducts [⁴CpTmCl₂(dme)], [Cp′YbCl₂(thf)₂], and [⁴CpLuCl₂(dme)], which were isolated from solutions in the corresponding donor solvent, the salt- and donor-free dihalides [Cp′TmCl₂]_n and [Cp′YbCl₂]_n were obtained as oligomers from pentane or petroleum ether extracts. The thulium compound gave [Cp′Tm{N(SiMe₃)₂}₂] with two equivalents of Na[N(SiMe₃)₂] and the ytterbium complex underwent ring exchange with lithium tert-butylcyclopentadienide and formation of the bis(tert-butylcyclopentadienyl)ytterbium complex [(Me₃CC₅H₄)₂Yb(μ-Cl)]₂.