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, TMEDA), small molecules (H2, SiH4, N2, CO), and molecules containing multiple C–C bonds (CH2CH2, PhCHCH2, trans-PhCHCHPh, cis-PhCHCHPh, CH2CH–CHCH2, Ph–CHCH–CHCH–Ph, PhCCPh, Me3SiCCSiMe3). Among compounds 1–3 only the samarium derivative 1 reacts with bipy and phenazine, affording SmIII complexes CpBn52Sm­(bipy–•) (5) and [(CpBn5)2Sm]2[μ-η3:η3-(C12H8N2)2–] (6). Complex 4 when illuminated with natural light undergoes redox reaction and in 72 h transforms into the mixed-valent compound {[CpBn5YbIIII2(μ-OMe)]2}2­{YbII(DME)3} (7), being a separated ion pair.