| 16969780 |
Lee CC, Ke WC, Chan KT, Lai CL, Hu CH, Lee HM: Nickel (II) complexes of bidentate N-heterocyclic carbene/phosphine ligands: efficient catalysts for Suzuki coupling of aryl chlorides. Chemistry. 2007;13(2):582-91.
Nickel (II) complexes of bidentate N-heterocyclic carbene (NHC)/phosphane ligand L were prepared and structurally characterized. Unlike palladium, which forms [PdCl (2)(L)], the stable nickel product isolated is the ionic [Ni (L)(2)] Cl (2). These Ni (II) complexes are highly robust in air. Among different N-substituents on the ligand framework, the nickel complex of ligand L bearing N-1-naphthylmethyl groups (2 a) is a highly effective catalyst for Suzuki cross-coupling between phenylboronic acid and a range of aryl halides, including unreactive aryl chlorides. The activities of 2 a are largely superior to those of other reported nickel NHC complexes and their palladium counterparts. Unlike the previously reported [NiCl (2)(dppe)] (dppe=1,2-bis (diphenylphosphino) ethane), 2 a can effectively catalyze the cross-coupling reaction without the need for a catalytic amount of PPh (3), and this suggests that the PPh (2) functionality of hybrid NHC ligand L can partially take on the role of free PPh (3). However, for unreactive aryl chlorides at low catalyst loading, the presence of PPh (3) accelerates the reaction. |
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