An unusual organoyttrium alkyl complex containing a [C_5HMe _3(η~3-CH_2)-C_5H_4N-κ] - ligand and an elusive cyclopentadienide-based scandium tuck-over Zwitterion obtained by C-H bond activation

摘要

The acid-base reaction between Y(CH_2SiMe_3) _3(thf)_2 and the pyridyl-functionalized cyclopentadienyl (Cp) ligand C_5Me_4H-C_5H_4N (1 equiv) at 0 °C afforded a mixture of two products: (η~5:κ- C_5Me_4-C_5H_4N)Y(CH_2SiMe _3)_2(thf) (1 a) and (η~5: κ-C_5Me_4-C_5H_4N)_2YCH_2SiMe_3 (1 b), in a 5:2 ratio. Addition of the same ligand (2 equiv) to Y(CH_2SiMe_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_5Me_4-C_5H_4N)[C_5HMe_3(η~3-CH_2)-C_5H_4N-κ]Y(CH_2SiMe_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_2SiMe_3) _3(thf)_2 and C_5Me_4H-C_5H_4N exclusively afforded the bis(alkyl) product (η~5:κ-C_5Me_4-C_5H_4N)Lu(CH_2SiMe_3)_2(thf) (2 a). Similarly, the reaction between the ligand (2 equiv) and Lu(CH 2SiMe 3) 3(thf) 2 gave the mono(alkyl) complex (η~5:κ-C_5Me_4-C_5H_4N)_2LuCH_2SiMe_3 (2 b), in which no ligand redistribution was observed. Strikingly, treatment of Sc(CH_2SiMe_3)_3(thf)_2 with C_5Me_4H-C_5H_4N 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_5Me_4-C_5H_4N)Sc(thf)[- η~5:η ~:κ-C_5Me_3(CH_2)-C_5H _4N]Sc(CH_2SiMe_3)_3. In the zwitterion, the dianionic ligand [C_5Me_3(CH_2)-C_5H_4N]~(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.