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Mixed Dicarboxylato−Bis(carbene) Complexes of Palladium(II): Synthesis, Structures, Trans−Cis Isomerism, and Catalytic Activity

2006; American Chemical Society; Volume: 25; Issue: 5 Linguagem: Inglês

10.1021/om0510369

1520-6041

Han Vinh Huynh, Tiong Cheng Neo, Geok Kheng Tan,

Catalytic C–H Functionalization Methods

Mixed dicarboxylato−bis(carbene) complexes of palladium(II) have been prepared by reacting cis-diiodo-bis(N,N'-dimethylbenzimidazolin-2-ylidene)palladium(II) (cis-A) with AgO2CR, where R = CH3, CF3, and CF2CF3. In this manner, cis-diacetato-bis(N,N'-dimethylbenzimidazolin-2-ylidene)palladium(II) (1), cis-di(trifluoroacetato)-bis(N,N'-dimethylbenzimidazolin-2-ylidene)palladium(II) (2), and cis-di(pentafluoropropionato)-bis(N,N'-dimethylbenzimidazolin-2-ylidene)palladium(II) (3) were obtained. Complexes 1−3 were fully characterized by multinuclear NMR spectroscopies as well as ESI mass spectrometry. X-ray crystal structure analyses of the first mixed carboxylato/benzimidazolin-2-ylidene complexes reveal mononuclear species with a square-planar palladium(II) center coordinated by two monodentate carbene and two monodentate carboxylato ligands in a cis arrangement. The cis configuration was found to be thermodynamically favored in this type of complexes. The results also show that the introduction of N-heterocyclic carbene ligands stabilizes the palladium−carboxylate moiety effectively, thus preventing both reductive decomposition and autoionization processes. A preliminary catalytic study revealed that complexes 1−3 are highly active in the Mizoroki−Heck coupling of aryl bromides and activated aryl chlorides.