Metalorganics and Inorganic Materials, Department of Chemistry, Technische Universität Berlin , Straße des 17, Juni 135, Sekr. C2, 10623 Berlin, Germany.
J Am Chem Soc. 2013 Oct 16;135(41):15617-26. doi: 10.1021/ja408137t. Epub 2013 Oct 4.
The first [ECE]Ni(II) pincer complexes with E = Si(II) and E = Ge(II) metallylene donor arms were synthesized via C-X (X = H, Br) oxidative addition, starting from the corresponding [EC(X)E] ligands. These novel complexes were fully characterized (NMR, MS, and XRD) and used as catalyst for Ni-catalyzed Sonogashira reactions. These catalysts allowed detailed information on the elementary steps of this catalytic reaction (transmetalation → oxidative addition → reductive elimination), resulting in the isolation and characterization of an unexpected intermediate in the transmetalation step. This complex, {[ECE]Ni acetylide → CuBr} contains both nickel and copper, with the copper bound to the alkyne π-system. Consistent with these unusual structural features, DFT calculations of the {[ECE]Ni acetylide → CuBr} intermediates revealed an unusual E-Cu-Ni three-center-two-electron bonding scheme. The results reveal a general reaction mechanism for the Ni-based Sonogashira coupling and broaden the application of metallylenes as strong σ-donor ligands for catalytic transformations.
通过 C-X（X = H，Br）氧化加成反应，从相应的[EC（X）E]配体出发，合成了第一个具有 E = Si（II）和 E = Ge（II）亚甲基供体臂的[ECE]Ni（II）钳形配合物。这些新型配合物经过了全面的表征（NMR、MS 和 XRD），并被用作 Ni 催化的 Sonogashira 反应的催化剂。这些催化剂为该催化反应的基本步骤提供了详细的信息（转金属化→氧化加成→还原消除），导致在转金属化步骤中分离并表征了一个意想不到的中间体。该配合物，{[ECE]Ni 炔烃→CuBr}包含镍和铜，铜与炔烃π-体系结合。与这些不寻常的结构特征一致，{[ECE]Ni 炔烃→CuBr}中间体的 DFT 计算揭示了一种不寻常的 E-Cu-Ni 三中心二电子成键方案。结果揭示了基于 Ni 的 Sonogashira 偶联的一般反应机制，并拓宽了亚甲基作为催化转化中强σ-供体配体的应用。
