Nonchelate and Chelate Complexes of Palladium(II) with N-Heterocyclic Carbene Ligands of Amido Functionality

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• 作者：Chuang-Yi Liao ; Kai-Ting Chan ; Jing-Yao Zeng ; Ching-Han Hu ; Cheng-Yi Tu ; Hon Man Lee
• 刊名：Organometallics
• 出版年：2007
• 出版时间：March 26, 2007
• 年：2007
• 卷：26
• 期：7
• 页码：1692 - 1702
• 全文大小：483K
• 年卷期：v.26,no.7(March 26, 2007)
• ISSN：1520-6041

文摘

The imidazolium ligand precursors [L¹H¹H²]Cl and [L²H¹₂H²]Cl (H¹ = NHC=O, H² = NCHN) forthe potentially bidentate and pincer-type amido-NHC ligands were synthesized in 66-78% yields. Selectivedeprotonation of H² in these salts with pyridine in the presence of palladium chloride resulted in themonodentate palladium(II) complexes Pd(L¹H¹)(py)Cl₂ and Pd(L²H¹₂)(py)Cl₂. The use of K₂CO₃ in pyridineor DMF led to the double and triple deprotonations of the ligand precursors, giving the bis-bidentate andpincer-type palladium(II) complexes PdL¹₂ and PdL²(py), respectively. Intriguingly, in certain cases, boththe cis and the trans isomers of PdL¹₂ were formed and isolated in pure forms. A theoretical study indicatesthat the trans-PdL¹₂ is thermodynamically more stable than the cis isomer (ca. 5.8 kcal mol^-1). All thenew complexes are characterized by NMR (1D and 2D) and single-crystal X-ray diffraction studies. Asystematic study of the new complexes in Suzuki coupling reactions revealed the following order ofactivities: Pd(L¹H¹)(py)Cl₂ > PdL²(py) > PdL¹₂.