Efficient heck reactions catalyzed by palladium(0) and -(II) complexes bearing n-heterocyclic carbene and amide functionalities

Jhen Yi Lee, Pi Yun Cheng, Yi Hua Tsai, Guan Ru Lin, Shih Pu Liu, Ming Han Sie, Hon Man Lee

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Abstract

A palladium(0) NHC complex Pd0(LH1)2(MA) (MA = maleic anhydride) was prepared from the amide-imidazolium salt [LH 1H2]Cl (H1 = NH proton; H2 NCHN proton). The X-ray diffraction studies confirmed that a η2-MA ligand and two monodentate NHC ligands with the H1 protons remaining intact are coordinated. These NH protons are involved in intra- or intermolecular hydrogen bonds stabilizing the solid-state structure. Degradation of Pd(LH1)2(MA) in air leads to the formation of the chelate complex trans-PdIIL2 and other unidentified products. Negative-ion electrospray mass spectrometry revealed some intriguing Pd(0) species, including a 14-electron [Pd0L]- species that bears only a bidentate NHC/amido ligand. The anionic amido group imparts a high electron density on a palladium center, as shown by X-ray photoelectron study. The palladium(0) precatalyst is highly efficient in catalyzing Heck reactions with activated aryl chlorides in ionic liquid. For deactivating aryl chlorides and bulky aryl bromides, cis-PdIIL2 is more effective. A range of Heck-coupled products can be prepared by Pd 0(LH1)2(MA) and cis-PdIIL 2. The latter complex also successfully mediates one-pot sequential Heck/Heck and Suzuki/Heck coupling reactions with 4-bromochlorobenzene as substrate.

Original languageEnglish
Pages (from-to)3901-3911
Number of pages11
JournalOrganometallics
Volume29
Issue number17
DOIs
Publication statusPublished - 2010 Sep 13

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All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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