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Chiral CNN Pincer Palladium(II) Complexes with 2‑Aryl-6-(oxazolinyl)pyridine Ligands: Synthesis, Characterization, and Application to Enantioselective Allylation of Isatins and Suzuki–Miyaura Coupling Reaction

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journal contribution
posted on 13.01.2014, 00:00 authored by Tao Wang, Xin-Qi Hao, Juan-Juan Huang, Kai Wang, Jun-Fang Gong, Mao-Ping Song
A series of chiral 2-aryl-6-(oxazolinyl)­pyridine (aryl = phenyl or 1-naphthyl) ligands 2af were conveniently prepared from commercially available 6-bromo-2-picolinaldehyde in two steps. Reaction of 2af with PdCl2 in toluene in the presence of sodium bicarbonate afforded the corresponding CNN pincer Pd­(II) complexes 3af via aryl C–H bond activation of the related ligands. All of the new compounds have been fully characterized by elemental analysis (MS for ligands), 1H and 13C NMR, and IR spectra. In addition, the molecular structures of Pd­(II) complexes 3cf have been determined by X-ray single-crystal diffraction. The obtained chiral pincer catalysts were successfully used in the asymmetric allylation of isatins with allyltributyltin, giving the corresponding 3-allyl-3-hydroxyoxindoles in high yields with enantioselectivities of up to 86% ee. These pincers could also catalyze the asymmetric Suzuki–Miyaura coupling reaction to provide the axially chiral biaryl products in good yields with good stereoselectivities (up to 68% ee).