An Unusual Organoyttrium Alkyl Complex Containing a [C5HMe3(eta(3)-CH2)-C5H4N-kappa](-) Ligand and an Elusive Cyclopentadienide-Based Scandium Tuck-Over Zwitterion Obtained by C-H Bond Activation

作者:Jian, ZB ; Cui, DM
关键字:C-H activation; coordination modes; cyclopentadienyl ligands; rare earths; zwitterions


 The acid–base reaction between Y(CH2SiMe3)3(thf)2 and the pyridyl-functionalized cyclopentadienyl (Cp) ligand C5Me4H[BOND]C5H4N (1?equiv) at 0?°C afforded a mixture of two products: (η5:κ-C5Me4[BOND]C5H4N)Y(CH2SiMe3)2(thf) (1?a) and (η5:κ-C5Me4[BOND]C5H4N)2YCH2SiMe3 (1?b), in a 5:2 ratio. Addition of the same ligand (2?equiv) to Y(CH2SiMe3)3(thf)2, however, generated 1?b together with the novel complex 1?c, the first well defined yttrium mono(alkyl) complex (η5:κ-C5Me4[BOND]C5H4N)[C5HMe3(η3-CH2)-C5H4N-κ]Y(CH2SiMe3) containing a rare κ/η3-allylic coordination mode in which the C[BOND]H bond activation occurs unexpectedly with the allylic methyl group rather than conventionally on Cp ring. If the central metal was changed to lutetium, the equimolar reaction between Lu(CH2SiMe3)3(thf)2 and C5Me4H[BOND]C5H4N exclusively afforded the bis(alkyl) product (η5:κ-C5Me4[BOND]C5H4N)Lu(CH2SiMe3)2(thf) (2?a). Similarly, the reaction between the ligand (2?equiv) and Lu(CH2SiMe3)3(thf)2 gave the mono(alkyl) complex (η5:κ-C5Me4[BOND]C5H4N)2LuCH2SiMe3 (2?b), in which no ligand redistribution was observed. Strikingly, treatment of Sc(CH2SiMe3)3(thf)2 with C5Me4H[BOND]C5H4N in either 1:1 or 1:2 ratio at 0?°C generated the first cyclopentadienide-based scandium zwitterionic “tuck-over” complex 3, (η5:κ-C5Me4[BOND]C5H4N)Sc(thf)[μ-η5:η1:κ-C5Me3(CH2)-C5H4N]Sc(CH2SiMe3)3. In the zwitterion, the dianionic ligand [C5Me3(CH2)-C5H4N]2? binds both to Sc13+ and to Sc23+, in η5 and η1/κ?modes. In addition, the reaction chemistry, the molecular structures, and the mechanism are also discussed in detail.