Ni^II 2,2′-bipyridine complexes are commonly invoked intermediates in metallaphotoredox cross-coupling reactions. Despite their ubiquity, design principles targeting improved catalytic performance remain underdetermined. A series of Ni(^Rbpy)(^R′Ar)Cl (R = MeOOC, t-Bu, R′ = CH₃, CF₃) complexes were proposed to have multiconfigurational electronic structures on the basis of multiconfigurational/multireference calculations, with significant mixing of Ni → bpy metal-to-ligand charge transfer (MLCT) configurations into the ground-state wave function. Here, Ni K-edge and L_2,3-edge X-ray absorption spectroscopies provide experimental support for the highly covalent and multiconfigurational electronic structures of these complexes. The pre-edge intensity in the K-edge spectrum reflects highly covalent Ni–aryl bonding. The L₃-edge spectral shape is dependent on ligand functionalization, and a feature reflecting the MLCT character is assigned using prior ab initio and new semiempirical calculations. The results suggest the push/pull effects of the aryl/bpy ligands moderate the changes in electron density on Ni during the multiredox cross-coupling reaction cycle.

中文翻译：

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X 射线吸收光谱揭示镍交叉偶联催化剂的多组态电子结构


Ni^II 2,2′-联吡啶配合物是金属光氧化还原交叉偶联反应中常用的中间体。尽管它们无处不在，但旨在提高催化性能的设计原则仍未确定。在多构型/多参比计算的基础上，提出了一系列 Ni（^Rbpy）（^R′Ar）Cl （R = MeOOC， t-Bu， R′ = CH₃， CF₃） 配合物具有多构型电子结构，其中 Ni → bpy 金属到配体电荷转移 （MLCT） 构型显着混合到基态波函数中。在这里，Ni K-edge 和 L_2,3-edge X 射线吸收光谱为这些配合物的高度共价和多构型电子结构提供了实验支持。K 边谱图中的前边强度反映了高度共价的 Ni-芳基键合。L₃ 边缘光谱形状取决于配体功能化，反映 MLCT 特征的特征是使用先前的从头开始和新的半经验计算分配的。结果表明，在多氧化还原交叉偶联反应循环中，芳基/bpy 配体的推/拉效应调节了 Ni 上电子密度的变化。