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

Metalation of Cp<sup>Bn5</sup>H with PhCH<sub>2</sub>K (1:1 molar ratio) and subsequent reactions with 0.5 equiv of LnI<sub>2</sub>(THF)<sub><i>n</i></sub> (Ln = Yb, Sm, Eu, <i>n</i> = 2, 3) (THF, 30 °C, 1 h) afforded new lanthanoidocenes (Cp<sup>Bn5</sup>)<sub>2</sub>Ln (Ln = Yb (<b>1</b>), Sm (<b>2</b>), Eu (<b>3</b>)), which were isolated in reasonable yields. The X-ray diffraction studies revealed that the obtained complexes adopt the structures of bent sandwiches (Cp<sub>Centr</sub>–Ln–Cp<sub>Centr</sub> = 141.8–142.9°). Complexes <b>1</b>–<b>3</b> 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 <i>o</i>-carbon atoms of two pendant Ph groups. The reaction of equimolar amounts of YbI<sub>2</sub>(THF)<sub>2</sub> and Cp<sup>Bn5</sup>K in DME afforded monocyclopentadienyl Yb­(II) complex [Cp<sup>Bn5</sup>Yb­(DME)­(μ-I)]<sub>2</sub> (<b>4</b>). Complex <b>4</b> 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 <b>1</b>–<b>3</b> were inert toward Lewis bases (THF, DME, PMe<sub>3</sub>, TMEDA), small molecules (H<sub>2</sub>, SiH<sub>4</sub>, N<sub>2</sub>, CO), and molecules containing multiple C–C bonds (CH<sub>2</sub>CH<sub>2</sub>, PhCHCH<sub>2</sub>, trans-PhCHCHPh, cis-PhCHCHPh, CH<sub>2</sub>CH–CHCH<sub>2</sub>, Ph–CHCH–CHCH–Ph, PhCCPh, Me<sub>3</sub>SiCCSiMe<sub>3</sub>). Among compounds <b>1</b>–<b>3</b> only the samarium derivative <b>1</b> reacts with bipy and phenazine, affording Sm<sup>III</sup> complexes Cp<sup>Bn5</sup><sub>2</sub>Sm­(bipy<sup>–•</sup>) (<b>5</b>) and [(Cp<sup>Bn5</sup>)<sub>2</sub>Sm]<sub>2</sub>[μ-η<sup>3</sup>:η<sup>3</sup>-(C<sub>12</sub>H<sub>8</sub>N<sub>2</sub>)<sup>2–</sup>] (<b>6</b>). Complex <b>4</b> when illuminated with natural light undergoes redox reaction and in 72 h transforms into the mixed-valent compound {[Cp<sup>Bn5</sup>Yb<sup>III</sup>I<sub>2</sub>(μ-OMe)]<sub>2</sub>}<sub>2</sub>­{Yb<sup>II</sup>(DME)<sub>3</sub>} (<b>7</b>), being a separated ion pair.