Lanthanide(II) complexes bearing linked cyclopentadienyl-anilido ligands: Synthesis, structures, and one-electron-transfer and ethylene polymerization reactions

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 pi -interaction. Reaction of 1 or 1 ' with azobenzene gave the binuclear Yb(III) complex Me2Si(C5Me4)(NPh)Yb(thf)(mu,eta (2):eta (3)-N2Ph2)Yb(NPh)(C5Me4)SiMe2 (3), which contains a cis-oriented azobenzene dianion unit bonding in a eta (3) fashion to one Yi, atom and in a eta (2) 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)(mu -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 M-n = 7.26 x 10(5) and M-w/M-n = 1.58.