期刊
CHEMPLUSCHEM
卷 79, 期 9, 页码 1294-1303出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cplu.201402135
关键词
bridging ligands; carbene ligands; cross-coupling; immobilization; palladium
资金
- TUM Graduate School
A new immobilization mode for methylene-bridged bis(NHC) (NHC=N-heterocyclic carbene) ligand systems is presented, allowing fine-tuning of the steric and electronic properties of the bidentate ligand. For example, four hydroxymethyl-functionalized imidazolium salts (1a-c and 2a) and three bis(NHC) Pd complexes 3a, 3b, and 4a are described. The chloro-functionalized bis(NHC) Pd complex 4a was obtained quantitatively by conversion of the hydroxyl substituent of complex 3a into a chloro substituent by employing thionyl chloride. All three bis(NHC) complexes 3a, 3b, and 4a were characterized by NMR spectroscopy, elemental analysis, mass spectrometry, and single-crystal X-ray diffraction. Two different synthetic routes were applied to immobilize the bis(NHC) Pd complex 3a on polystyrene. The obtained heterogeneous catalyst 5b was utilized for Suzuki-Miyaura cross-coupling reactions and could be recycled without significant activity loss in four runs. Furthermore, the water-soluble homogeneous catalyst 3a itself could be employed for Suzuki-Miyaura cross-coupling reactions in water.
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