AbstractHerein, we report for the first time the use of the nitrogen‐based bidentate molecule [2.2]pyridinophane (N2) as a ligand for metal complexes. Additionally, its improved synthesis allows for electronic modification of the pyridine rings to access the new para‐dimethylamino‐[2.2]pyridinophane ligand (p‐NMe2N2). These ligands bind nickel in an analogous fashion to other pyridinophane ligands, completing the series of tetra‐, tri‐, and bidentate pyridinophane‐nickel complexes. The new compounds exhibit geometrically enforced C−H anagostic interactions between the ethylene bridge protons and the nickel center that are not present in other pyridinophane systems. These ethylene bridge groups also act as an unusual form of steric encumbrance, enforcing square planar geometries in ligand fields that would otherwise adopt tetrahedral structures. In addition, these anagostic interactions inhibit the catalytic performance in Csp3–Csp3 Kumada cross coupling reactions relative to other common bidentate N‐ligand platforms, possibly by preventing the formation of the 5‐coordinate oxidative addition intermediates.
摘要在本文中,我们首次报告了氮基双叉分子[2.2]吡啶玢(N2)作为金属络合物配体的用途。此外,通过改进其合成方法,可以对吡啶环进行电子修饰,从而获得新的对二甲氨基-[2.2]吡啶玢配体(p-NMe2N2)。这些配体以类似于其他吡啶配体的方式与镍结合,从而完成了四齿、三齿和双齿吡啶-镍配合物系列。这些新化合物的乙烯桥质子和镍中心之间表现出几何上强制的 C-H 负向相互作用,这是其他吡啶烷系统所不具备的。这些乙烯桥基团还充当了一种非同寻常的立体阻碍形式,在配体场中强制形成方形平面几何结构,否则这些配体就会采用四面体结构。此外,与其他常见的双齿 N 配体平台相比,这些助燃相互作用抑制了 Csp3-Csp3 Kumada 交叉偶联反应的催化性能,这可能是通过阻止形成 5 配位氧化加成中间体实现的。