Nelson Kacie J, Kazmierczak Nathanael P, Cagan David A, Follmer Alec H, Scott Thais R, Raj Sumana L, Garratt Douglas, Powers-Riggs Natalia, Gaffney Kelly J, Hadt Ryan G, Cordones Amy A
Stanford PULSE Institute, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, United States.
Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, United States.
J Phys Chem Lett. 2025 Jan 9;16(1):87-94. doi: 10.1021/acs.jpclett.4c02917. Epub 2024 Dec 19.
Ni 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(bpy)(Ar)Cl (R = MeOOC, -Bu, R' = CH, CF) 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-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 L-edge spectral shape is dependent on ligand functionalization, and a feature reflecting the MLCT character is assigned using prior 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.
镍（II）-2,2'-联吡啶配合物通常被认为是金属光氧化还原交叉偶联反应中的中间体。尽管它们普遍存在，但针对提高催化性能的设计原则仍未完全确定。基于多组态/多参考计算，一系列Ni(bpy)(Ar)Cl（R = MeOOC、-Bu，R' = CH、CF）配合物被认为具有多组态电子结构，Ni→bpy的金属到配体电荷转移（MLCT）组态与基态波函数有显著混合。在此，Ni K边和L边X射线吸收光谱为这些配合物的高共价和多组态电子结构提供了实验支持。K边光谱中的前缘强度反映了高度共价的Ni-芳基键合。L边光谱形状取决于配体官能化，并且利用先前的和新的半经验计算确定了一个反映MLCT特征的峰。结果表明，芳基/联吡啶配体的推/拉效应在多氧化还原交叉偶联反应循环中缓和了镍上电子密度的变化。
