A New Heteroatom Coordination Promoted Homolysis of the Yb−N Bond. Synthesis and Structural Characterization of a New Class of Ytterbium(II) and Ytterbium(III) Complexes with Amido and Indenyl Ligands and Catalytic Activities of Ytterbium(II) Complexes

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Abstract

Reaction of Me2Si(Me2NCH2CH2C9H6)Cl with 1 equiv of t-BuNHLi yielded Me2Si(Me2NCH2CH2C9H6)(t-BuNH) (1). Treatment of Me2NCH2CH2C9H7 with 1 equiv of n-BuLi, followed by reaction with an excess of Me3SiCl, produced Me2NCH2CH2C9H6SiMe3 (2) in 79% yield. Interaction of YbCl3 with 3 equiv of (Me3Si)2NLi in THF, after workup, produced the tetracoordinate ytterbium(III) amide [(Me3Si)2N]3YbIII(μ-Cl)Li(THF)3 (3) in 85% yield. Treatment of 3 with 2 equiv of 1 gave the ytterbium(II) complex [η5:η1-Me2Si(Me2NCH2CH2C9H5)(t-BuNH)]2YbII (4) in 58% yield via a reductive reaction. To get some insight into the reaction, several reactions were initiated to study the effects of the t-BuNH group, silyl group, and N,N-dimethylaminoethyl group of the indene compounds, effects of coordinate ClLi(THF)3 in 3, and temperature effect on the reductive reaction. Treatment of 3 with 2 equiv of 2 afforded (η5:η1-Me2NCH2CH2C9H5SiMe3)2YbII (5) in 52% yield. Interaction of 3 with 2 equiv of Me2NCH2CH2C9H7 produced a ytterbium(II) complex (η5:η1-Me2NCH2CH2C9H6)2YbII (6) in 63% yield. Treatment of the ytterbium(III) complex [(Me3Si)2N]3YbIII with 2 equiv of Me2NCH2CH2C9H7 also afforded the ytterbium(II) complex (η5:η1-Me2NCH2CH2C9H6)2YbII (6) in 62% yield, which provides an alternate method for the preparation of 6. Treatment of 3 with 2 equiv of indene(C9H8) produced the ytterbium(III) complex (η5-C9H7)2YbIIIN(SiMe3)2 (7). Treatment of 3 with 1 equiv of 1,2-bis(indenyl)ethane also produced the ytterbium(III) complex meso-[ethylenebis(η5-indenyl)ytterbiumIII bis(trimethylsily)amide ((EBI)YbIIIN(SiMe3)2) (8). All the compounds were fully characterized by spectroscopic methods and elemental analyses. Complexes 3, 4, 5, 6, and 8 were additionally characterized by a single-crystal X-ray diffraction study. The formation pathway for the ytterbium(II) complexes is proposed. The study showed that ytterbuim(II) complexes 4, 5, and 6 can function as single-component MMA polymerization catalysts with good activity.

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