title: An unusual organoyttrium alkyl complex containing a [C5HMe3(η(3)-CH2)-C5H4N-κ]- ligand and an elusive cyclopentadienide-based scandium tuck-over zwitterion obtained by C-H bond activation.
abstract: The acid-base reaction between Y(CH(2)SiMe(3))(3)(thf)(2) and the pyridyl-functionalized cyclopentadienyl (Cp) ligand C(5)Me(4)H-C(5)H(4)N (1 equiv) at 0 °C afforded a mixture of two products: (η(5):κ-C(5)Me(4)-C(5)H(4)N)Y(CH(2)SiMe(3))(2)(thf) (1 a) and (η(5):κ-C(5)Me(4)-C(5)H(4)N)(2)YCH(2)SiMe(3) (1 b), in a 5:2 ratio. Addition of the same ligand (2 equiv) to Y(CH(2)SiMe(3))(3)(thf)(2), however, generated 1 b together with the novel complex 1 c, the first well defined yttrium mono(alkyl) complex (η(5):κ-C(5)Me(4)-C(5)H(4)N)[C(5)HMe(3)(η(3)-CH(2))-C(5)H(4)N-κ]Y(CH(2)SiMe(3)) containing a rare κ/η(3)-allylic coordination mode in which the C-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(CH(2)SiMe(3))(3)(thf)(2) and C(5)Me(4)H-C(5)H(4)N exclusively afforded the bis(alkyl) product (η(5):κ-C(5)Me(4)-C(5)H(4)N)Lu(CH(2)SiMe(3))(2)(thf) (2 a). Similarly, the reaction between the ligand (2 equiv) and Lu(CH(2)SiMe(3))(3)(thf)(2) gave the mono(alkyl) complex (η(5):κ-C(5)Me(4)-C(5)H(4)N)(2)LuCH(2)SiMe(3) (2 b), in which no ligand redistribution was observed. Strikingly, treatment of Sc(CH(2)SiMe(3))(3)(thf)(2) with C(5)Me(4)H-C(5)H(4)N in either 1:1 or 1:2 ratio at 0 °C generated the first cyclopentadienide-based scandium zwitterionic "tuck-over" complex 3, (η(5):κ-C(5)Me(4)-C(5)H(4)N)Sc(thf)[μ-η(5):η(1):κ-C(5)Me(3)(CH(2))-C(5)H(4)N]Sc(CH(2)SiMe(3))(3). In the zwitterion, the dianionic ligand [C(5)Me(3)(CH(2))-C(5)H(4)N](2-) binds both to Sc1(3+) and to Sc2(3+), in η(5) and η(1)/κ modes. In addition, the reaction chemistry, the molecular structures, and the mechanism are also discussed in detail.
authors.affiliation: State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun 130022, China.
authors.forename: Zhongbao
authors.initials: Z
authors.lastname: Jian
authors.forename: Dongmei
authors.initials: D
authors.lastname: Cui