Base-free lanthanoidocenes(II) coordinated by bulky pentabenzylcyclopentadienyl ligands

Abstract

Metalation of Cp Bn5 H with PhCH 2 K (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 °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°). 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 YbI 2 (THF) 2 and Cp Bn5 K in DME afforded monocyclopentadienyl Yb(II) complex [Cp Bn5 Yb(DME)(-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, PMe 3, TMEDA), small molecules (H 2, SiH 4, N 2, CO), and molecules containing multiple C-C bonds (CH 2 =CH 2, PhCH=CH 2, trans-PhCH=CHPh, cis-PhCH=CHPh, CH 2 =CH-CH=CH 2, Ph-CH=CH-CH=CH-Ph, PhC≡CPh, Me 3 SiC≡CSiMe 3). Among compounds 1-3 only the samarium derivative 1 reacts with bipy and phenazine, affording Sm III complexes Cp Bn5 2 Sm(bipy -) (5) and [(Cp Bn5) 2 Sm] 2 [-η 3 :η 3 -(C 12 H 8 N 2) 2- ] (6). Complex 4 when illuminated with natural light undergoes redox reaction and in 72 h transforms into the mixed-valent compound {[Cp Bn5 Yb III I 2 (-OMe)] 2 } 2 {Yb II (DME) 3 } (7), being a separated ion pair.