AbstractWe report a facile synthetic method for accessing rare T‐shaped Ni0 species, stabilised by low‐coordinate cationic germylene and stannylene ligands which behave as Z‐type ligands toward Ni0. An in‐depth computational analysis indicates significant Nid→Ep donation (E=Ge, Sn), with essentially no E→Ni donation. The tetrylene ligand's Lewis acidity can be modulated in situ through the addition of a donor ligand, which selectively binds at the Lewis acidic tetrylene site. This switches this binding centre from a Z‐type to a classical L‐type ligand, with a concomitant geometry switch at Ni0 from T‐shaped to trigonal planar. Exploring the effects of this geometry switch in catalysis, isolated T‐shaped complexes 3 a–c and 4 a–c are capable of the hydrogenation of alkenes under mild conditions, whilst the closely related trigonal planar and tetrahedral Ni0 complexes 5, D, and E, which feature L‐type chloro‐ or cationic‐tetrylene ligands, are inactive under these conditions. Further, addition of small amounts of N‐bases to the catalytic systems involving T‐shaped complexes significantly reduces turnover rates, giving evidence for the in situ modulation of ligand electronics for catalytic switching.
摘要 我们报告了一种获得稀有 T 型 Ni0 物种的简便合成方法,该物种由低配位阳离子
锗烯和
锡烯
配体稳定,这些
配体对 Ni0 来说是 Z 型
配体。 深入的计算分析表明,存在大量的 Nid→Ep 捐献(E=Ge、Sn),基本上没有 E→Ni 捐献。通过添加供体
配体,可以在原位调节四亚甲基
配体的
路易斯酸度,供体
配体会选择性地与
路易斯酸性的四亚甲基位点结合。这就将该结合中心从 Z 型
配体转换为经典的 L 型
配体,同时在 Ni0 处的几何形状也从 T 型转换为三棱锥平面。为了探索这种几何转换在催化作用中的影响,分离出的 T 型配合物 3 a-c 和 4 a-c 能够在温和的条件下对烯烃进行氢化反应,而与之密切相关的三叉平面和四面体 Ni0 配合物 5、D 和 E(具有 L 型
氯或阳离子-
三甲苯配体)则在这些条件下不起作用。此外,在涉及 T 型配合物的催化体系中加入少量 N-碱会显著降低周转率,从而证明了原位调节
配体电子元件以实现催化转换。