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

Metalation of (CPH)-H-Bn5 with PhCH2K (1:1 molar ratio) and subsequent reactions with 0.5 equiv of LnI(2)(THF)(n) (Ln = Yb, Sm, Eu, n = 2, 3) (THF, 30 degrees C, 1 h) afforded new lanthanoidocenes (Cp-Bn5)(2)Ln (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 (Cp-Centr-Ln-Cp-Centr = 141.8-142.9 degrees). 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 (CpK)-K-Bn5 in DME afforded monocyclopentadienyl Yb(II) complex [(CpYb)-Yb-Bn5(DME)(mu-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 (H-2, SiH4, N-2, 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 Sm-III complexes (Cp2Sm)-Sm-Bn5(bipy(-center dot)) (5) and [(Cp-Bn5)(2)Sm](2)[mu-eta(3):eta(3)-(C12H8N2)(2-)] (6). Complex 4 when illuminated with natural light undergoes redox reaction and in 72 h transforms into the mixed-valent compound {[(CpYbI2)-Yb-Bn5-I-III(mu-OMe)](2)}(2){Yb-II(DME)(3)} (7), being a separated ion pair.