Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS), Université de Strasbourg, 4 rue Blaise Pascal, 67081, Strasbourg Cedex, France.
Laboratoire de Chimie Quantique, Institut de Chimie (UMR 7177 CNRS), Université de Strasbourg, 4 rue Blaise Pascal, 67081, Strasbourg Cedex, France.
Angew Chem Int Ed Engl. 2017 Oct 2;56(41):12557-12560. doi: 10.1002/anie.201706581. Epub 2017 Aug 31.
The imidazolium chloride [C H N(C H NMe )N{C(Me)(=NDipp)}]Cl (1; Dipp=2,6-diisopropyl phenyl), a potential precursor to a tritopic N C N pincer-type ligand, reacted with [Ni(cod) ] to give the Ni -Ni complex 2, which contains a rare cod-derived η -allyl-type bridging ligand. The implied intermediate formation of a nickel hydride through oxidative addition of the imidazolium C-H bond did not occur with the symmetrical imidazolium chloride [C H N {C(Me)(=NDipp)} ]Cl (3). Instead, a Ni-C(sp ) bond was formed, leading to the neutral N CHN pincer-type complex Ni[C H N {C(Me)(=NDipp)} ]Cl (4). Theoretical studies showed that this highly unusual feature in nickel NHC chemistry is due to steric constraints induced by the N substituents, which prevent Ni-H bond formation. Remarkably, ethylene inserted into the C(sp )-H bond of 4 without nickel hydride formation, thus suggesting new pathways for the alkylation of non-activated C-H bonds.
氯化 1-（N-甲基-N-（2,6-二异丙基苯基）咪唑啉-2-亚基）-N-甲基-N-（2,6-二异丙基苯基）甲脒（[C H N(C H NMe )N{C(Me)(=NDipp)}]Cl，1；Dipp=2,6-二异丙基苯基）是一种潜在的三齿 N C N 型钳式配体前体，与[Ni(cod) ]反应生成含有罕见的 cod 衍生的 η -烯丙基型桥联配体的 Ni-Ni 配合物 2。通过咪唑鎓 C-H 键的氧化加成形成镍氢化物的隐含中间步骤并未发生在对称的咪唑鎓氯化物[C H N {C(Me)(=NDipp)} ]Cl（3）中。相反，形成了 Ni-C（sp ）键，导致中性 N CHN 型钳式配合物 Ni[C H N {C(Me)(=NDipp)} ]Cl（4）的形成。理论研究表明，镍 NHC 化学中这种非常不寻常的特征是由于 N 取代基引起的空间位阻所致，这阻止了 Ni-H 键的形成。值得注意的是，乙烯插入 4 的 C(sp ）-H 键中而没有镍氢化物的形成，从而为非活化 C-H 键的烷基化提供了新途径。
