Cation size dependent reactivity of lanthanide trihalides with bulky alkylcyclopentadienyl anions

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.