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)(3)C5H2) 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 [((Cp2Ce)-Cp-4)(mu-Cl)(2)Na(tmeda)(2)](infinity) (Cp-4 = (Me2CH)(4)C5H) could be extracted from the product mixture with tetramethylethylenediamine and crystallized as a zigzag chain polymer. [(Cp2SmCl2Na)-Cp-4(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 (mu-OCH2CH2OCH3)](2) from cleavage of the dimethoxyethane solvent and with lutetium trichloride the hexanuclear complex [((CpLu)-Cp-4)(5)LuCl13(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 LnI(3). [(CpTmI)-Cp-4-Tm-2] 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'Sm-2] 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 [(CpTmCl2)-Cp-4(dme)], [Cp'YbCl2(thf)(2)], and [(CpLuCl2)-Cp-4(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)(2)Yb(mu-Cl)](2).