The amount of cooperation between the metal centers by tailored ligand design is vital to achieve the multimetallic catalytic benefits. Herein, a bimetallic Pd^II NHC/pyridine complex is synthesized utilizing a novel extended C₂-symmetric bis-NHC ligand featuring 1,4-disubstituted ethynylbenzene as a central ligand platform. The complex was further employed for the preparation of a dinuclear complex possessing a combination of NHC and PPh₃ ligands. Dinuclear complexes have also been synthesized using a 1,4-di(NHC)-substituted parent benzene ring platform with no acetylene linker units. The donor strengths of both bis-NHC ligands were compared with the help of ¹³C and ³¹P chemical shift values as probes. All of the bimetallic complexes were tested as precatalysts in the intermolecular α-arylation of 1-methyl-2-oxindole and Sonogashira coupling reactions. The dinuclear Pd^II complexes with the ethynylbenzene-bridged bis-NHC ligand showed impressive catalytic outcomes that outweigh the catalytic outcomes obtained with dinuclear bis-NHC complexes possessing no such acetylene linkers. The corresponding mononuclear Pd^II complexes were synthesized for comparison purposes utilizing both types of central ligand platforms. The dinuclear complexes appeared more active than the corresponding mononuclear complexes in catalysis. Furthermore, higher cooperative index values were obtained in catalysis using the dinuclear Pd^II complexes with an acetylene-bridged bis-NHC ligand compared to those with no such acetylene linkers.

中文翻译：

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基于乙基苯基的 PdII Bis（NHC） 相对于苯基 PdII Bis（NHC） 的催化优势：深入了解结构方面和供体强度探测


通过定制配体设计，金属中心之间的合作量对于实现多金属催化优势至关重要。在此，利用以 1,4-二取代乙炔苯为中心配体平台的新型扩展 C₂-对称双 NHC 配体合成了双金属 Pd^II NHC/吡啶配合物。该配合物进一步用于制备具有 NHC 和 PPh₃ 配体组合的双核配合物。偶核配合物也是使用没有乙炔接头单元的 1,4-di（NHC） 取代的母苯环平台合成的。在 ¹³C 和 ³¹P 化学位移值作为探针的帮助下，比较了两种 bis-NHC 配体的供体强度。所有双金属配合物均作为 1-甲基-2-氧吲哚 和 Sonogashira 偶联反应的分子间 α-芳基化反应中的预催化剂进行了测试。与乙炔苯桥的双 NHC 配体的双核 Pd^II 配合物显示出令人印象深刻的催化结果，超过了不具有这种乙炔连接剂的双核 bis-NHC 配合物获得的催化结果。利用两种类型的中央配体平台合成相应的单核 Pd^II 复合物以进行比较。在催化中，双核复合物似乎比相应的单核复合物更活跃。此外，与没有这种乙炔连接剂的配合物相比，使用具有乙炔桥双 NHC 配体的双核 Pd^II 配合物在催化中获得更高的合作指数值。