Threefold cation-π bonding in trimethylsilylated allyl complexes
Threefold cation-π bonding in trimethylsilylated allyl complexes
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DOI：
10.1021/om061174d
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发表时间：
2007-03-26
期刊：
影响因子：
2.8
通讯作者：
Rheingold, Arnold L.
中科院分区：
文献类型：
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作者：
Gren, Cameron K.;Hanusa, Timothy P.;Rheingold, Arnold L.
三氟甲磺酸锌与双(1,3-三甲基硅基)烯丙基阴离子的锂盐、钠盐和钾盐反应，M[A'] (A' = [1,3-(SiMe3)(2)C3H3])，生成三烯丙基锌酸盐 Li[ZnA'(3)] (1)、Na[ZnA'(3)] (2) 和 K[ZnA'(3)] (3)，而不是最初预期为中性 ZnA'(2)。这些分子在溶液中是流动的，并且 C6D6 中的分子的化学位移对于这三个分子来说是不同的，表明阳离子仍然与三烯丙基锌阴离子相关联。 2和3的单晶X射线结构表明，三个烯丙基配体以近似C-3对称的排列与锌结合，碱金属阳离子位于烯丙基配体的双键之间。距离与非共价阳离子-π 相互作用一致。锂衍生物1的结构与2和3相似，但金属-碳距离的不对称性表明涉及一些Li-C σ键。使用 PBE1PBE 泛函和三 zeta 质量的基组对 [M(C6H6)](+) 和 [M(C2H4)(n)](+)（M = Li、Na、K；n = 1-3）阳离子进行密度泛函理论计算。三种金属与两个乙烯分子或苯的结合焓（Delta H 度）大致相同，尽管后者的π电子数量较多。三个乙烯分子与金属阳离子的结合能超过苯的结合能 30-50%，强调了几何因素对阳离子-π 相互作用的重要性。
Reaction of zinc triflate with the lithium, sodium, and potassium salts of the bis(1,3-trimethylsilyl)allyl anion, M[A'] (A' = [1,3-(SiMe3)(2)C3H3]), produces the triallylzincates Li[ZnA'(3)] (1), Na[ZnA'(3)] (2), and K[ZnA'(3)] (3) rather than the inititially expected neutral ZnA'(2). The molecules are fluxional in solution, and the chemical shifts of the molecules in C6D6 are different for the three molecules, indicating that the cations remain associated with the triallylzinc anion. Single-crystal X-ray structures of 2 and 3 reveal that the three allyl ligands are bound to the zinc in an arrangement with approximate C-3 symmetry, with the alkali-metal cations situated between the double bonds of the allyl ligands. The distances are consistent with noncovalent cation-pi interactions. The structure of the lithium derivative 1 is similar to those of 2 and 3, but the asymmetry in the metal-carbon distances suggests that some Li-C sigma-bonding is involved. Density functional theory calculations were performed on [M(C6H6)](+) and [M(C2H4)(n)](+) (M = Li, Na, K; n = 1-3) cations with the PBE1PBE functional and basis sets of triple-zeta quality. The binding enthalpies (Delta H degrees) of the three metals to two ethylene molecules or to benzene are approximately the same, despite the latter's greater number of pi-electrons. The binding energy of three ethylene molecules to the metal cations exceeds that of benzene by 30-50%, underscoring the importance of geometric factors to cation-pi interactions.