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http://ir.ncue.edu.tw/ir/handle/987654321/10077
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| Title: | A New Tridentate Pincer Phosphine/N-Heterocyclic Carbene Ligand: Palladium Complexes, their Structures, and Catalytic Activities |
| Authors: | Lee, H. M.;Zeng, J. Y.;Hu, Ching-Han;Lee, M. T. |
| Contributors: | 化學系 |
| Date: | 2004-10
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| Issue Date: | 2012-05-03T06:17:50Z
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| Publisher: | American Chemical Society |
| Abstract: | A new imidazolium salt, 1,3-bis(2-diphenylphosphanylethyl)-3H-imidazol-1-ium chloride (2), for the phosphine/N-heterocyclic carbene-based pincer ligand, PCNHCP, and its palladium complexes were reported. The complex, [Pd(PCNHCP)Cl]Cl (4), was prepared by the common route of silver carbene transfer reaction and a novel direct reaction between the ligand precursor, PCNHCP·HCl and PdCl2 without the need of a base. Metathesis reactions of 4 with AgBF4 in acetonitrile produced [Pd(PCNHCP)(CH3CN)](BF4)2 (5). The same reaction in the presence of excess pyridine gave [Pd(PCNHCP)(py)](BF4)2 (6). The X-ray structure determination on 4−6 revealed the chiral twisting of the central imidazole rings from the metal coordination plane. In solution, fast interconversion between left- and right-twisted forms occurs. The twisting reflects the weak π-accepting property of the central NHC in PCNHCP. The uneven extent of twisting among the three complexes further implies the low rotational barrier about the Pd−NHC bond. Related theoretical computations confirm the small rotational energy barrier about the Pd−NHC bond (ca. 4 kcal/mol). Catalytic applications of 4 and 5 have shown that the complexes are modest catalysts in Suzuki coupling. The complexes were active catalysts in Heck coupling reactions with the dicationic complex 5 being more effective than the monocationic complex 4. |
| Relation: | Inorg. Chem., 43(21): 6822-6829 |
| Appears in Collections: | [化學系] 期刊論文
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