Lanthanide(II) Complexes Bearing Linked Cyclopentadienyl−Anilido Ligands:  Synthesis, Structures, and One-Electron-Transfer and Ethylene Polymerization Reactions

Abstract

Reactions of Ln[N(SiMe3)2]2(thf)2 (Ln = Sm, Yb) with 1 equiv of (C5Me4H)SiMe2NHPh afforded the first linked cyclopentadienyl−anilido (or amido) lanthanide(II) complexes Me2Si(C5Me4)(NPh)Ln(thf)x (1, Ln = Yb, x = 3; 2, Ln = Sm, x = 0−1) in 75−84% isolated yields. Recrystallization of 1 from toluene/hexane yielded the less solvated complex [Me2Si(C5Me4)(NPh)Yb(thf)]2 (1‘). Complex 1 adopts a monomeric structure containing one chelating Cp−anilido ligand and three thf ligands, while 1‘ forms a dimeric structure through an “intermolecular” Yb−Ph π-interaction. Reaction of 1 or 1‘ with azobenzene gave the binuclear Yb(III) complex Me2Si(C5Me4)(NPh)Yb(thf)(μ,η2: η3-N2Ph2)Yb(NPh)(C5Me4)SiMe2 (3), which contains a cis-oriented azobenzene dianion unit bonding in a η3 fashion to one Yb atom and in a η2 fashion to the other Yb atom. Reaction of 1 with 1 equiv of fluorenone gave the corresponding Yb(III) ketyl complex Me2Si(C5Me4)(NPh)Yb(thf)2(OC13H8) (4) in 75% isolated yield. Treatment of 4 with hexane/ether led to formation of the pinacolate complex [Me2Si(C5Me4)(NPh)Yb(thf)]2(μ-O2C26H16) (5), in which the pinacolate unit is arranged in a gauche conformation. Dissolving of 5 in THF cleaved the central C−C bond of the pinacolate unit in 5 and regenerated 4 quantitatively. The Sm(II) complex 2 showed moderate activity (44.8 kg of polymer (mol of Sm)-1 h-1) for the polymerization of ethylene under 1 atm at room temperature, yielding linear polyethylene with Mn = 7.26 × 105 and Mw/Mn = 1.58.