Non-classical early lanthanide(II) tris(di-tert-butylcyclopentadienyl) complexes

We report the synthesis of a series of temperature-sensitive non-classical early Ln(II) (Ln = lanthanide) complexes, [K(2.2.2 cryptand)][Ln(Cptt)3] (Cptt = C5H3tBu2-1,3; 1-Ln; Ln = La-Nd). Complexes 1-Ln were typically prepared using Schlenk line techniques rather than more common glove box protocols, by the reduction of the parent Ln(III) complexes [Ln(Cptt)3] (2-Ln) with KC8 in THF in the presence of 2.2.2-cryptand at –30 °C. The majority of the 2-Ln series have been reported previously by the salt metathesis reactions of 3 eq. KCptt with parent LnCl3, and these methods were adapted here to afford 2-Pr. Complexes 1-Ln and 2-Pr were characterized by single crystal XRD, elemental analysis, ATR IR and UV-Vis-NIR spectroscopy; 1-La and 2-Pr were additionally characterized by c.w. EPR spectroscopy, and variable temperature magnetic susceptibility measurements were performed on 2 Pr. During attempts to synthesize 2-Nd and 2-Sm we also obtained small crops of crystals of [Nd(Cptt)2(μ-I)]2 (3) and [Sm(Cptt)2(μ-Cl)]2·C7H8 (4·C7H8), respectively; these complexes were also structurally authenticated. The combination of data obtained indicate that the Ln(II) centers in 1-Ln adopt 4fn5d1 electron configurations, in common with other literature examples of [Ln(CpR)3]– anions (CpR = substituted cyclopentadienyl) for these metals.