The tetradentate ligands RN4 (RN4 = N,N′-di-alkyl-2,11-diaza[3,3](2,6)pyridinophane, R = Me or iPr) were found to stabilize cationic (RN4)PdMe2 and (RN4)PdMeCl complexes in both PdIII and PdIV oxidation states. This allows for the first time a direct structural and reactivity comparison of the two Pd oxidation states in an identical ligand environment. The PdIII complexes exhibit a distorted octahedral geometry, as expected for a d7 metal center, and display unselective C–C and C–Cl bond formation reactivity. By contrast, the PdIV complexes have a pseudo-octahedral geometry and undergo selective non-radical C–C or C–Cl bond formation that is controlled by the ability of the complex to access a five-coordinate intermediate.
四齿
配体RN4(RN4 = N,N′-二烷基-2,11-二氮杂[3,3](2,6)
吡啶并环,R = Me或iPr)能够稳定阳离子(RN4)PdMe2和(RN4)PdMeCl配合物在PdIII和PdIV氧化态下的结构。这使得首次能够在相同的
配体环境下直接比较两种Pd氧化态的结构和反应活性。PdIII配合物呈现出扭曲的八面体几何构型,正如预期的d7
金属中心所表现的那样,并且表现出对C–C和C–H键形成的无选择性反应活性。相比之下,PdIV配合物具有伪八面体几何构型,并经历由配合物能否形成五配位中间体控制的非自由基选择性C–C或C–Cl键形成反应。