Five palladium(II) complexes bearing potentially tetradentate pyridine-functionalized diNHC ligands with flexible linkers have been synthesized and characterized to study how coordination modes can be controlled by design and electronic factors. A combination of analytical techniques, including single-crystal X-ray diffraction and conductivity measurements, reveal that more strongly donating benzimidazole-derived NHCs induce tridentate coordination to form cationic N,C,C-pincer complexes, while more weakly donating 1,2,4-triazolinylidenes form neutral dibromido-dicarbene complexes with two pendant pyridyl groups. Increasing the flexibility between pyridyl and NHC units gives rise to a dicationic complex with a tetradentate ligand involving coordination of all four donors. The electronic influences from the different NHC donors can be rationalized by a Gutmann analysis.

中文翻译：

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控制吡啶基官能化的N-杂环二卡宾配体的配位模式

已合成并表征了五种带有潜在的四齿吡啶官能化diNHC配体和柔性接头的钯（II）配合物，以研究如何通过设计和电子因素控制配位模式。分析技术的结合，包括单晶X射线衍射和电导率测量，揭示出更强地捐赠的苯并咪唑衍生的NHC诱导三齿配位形成阳离子N，C，C-钳配合物，而较弱地提供1,2,4-三唑啉基形成具有两个侧基吡啶基的中性二溴-二碳烯配合物。吡啶基和NHC单元之间的柔性增加，会形成具有四齿配体的二齿复合物，涉及所有四个供体的配位。来自不同NHC捐助者的电子影响可以通过Gutmann分析得到合理化。