Base-Free Lanthanoidocenes(II) Coordinated by Bulky Pentabenzylcyclopentadienyl Ligands.

Metalation of CpBn5H with PhCH2K (1:1 molar ratio) and subsequent reactions with 0.5 equiv of LnI2(THF)n (Ln = Yb, Sm, Eu, n = 2, 3) (THF, 30 °C, 1 h) afforded new lanthanoidocenes (CpBn5)2Ln (Ln = Yb (1), Sm (2), Eu (3)), which were isolated in reasonable yields. The X-ray diffraction studies revealed that the obtained complexes adopt the structures of bent sandwiches (CpCentr–Ln–CpCentr = 141.8–142.9°). Complexes 1–3 do not contain coordinated Lewis base molecules directly after recrystallization from toluene at ambient temperature; however they feature short contacts between Ln(II) ions and o-carbon atoms of two pendant Ph groups. The reaction of equimolar amounts of YbI2(THF)2 and CpBn5K in DME afforded monocyclopentadienyl Yb(II) complex [CpBn5Yb(DME)(μ-I)]2 (4). Complex 4 proved to be a centrosymmetric iodo-bridged dimer with trans-disposed cyclopentadienyl ligands, and no interactions of the Yb(II) ion with pendant Ph groups were detected. Complexes 1–3 were inert toward Lewis bases (THF, DME, PMe3...