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Chiral (phosphine)-(imidazoline) PCN pincer palladium(ii) complexes: synthesis and application in asymmetric hydrophosphination of 2-alkenoylpyridines with diphenylphosphine†
Jun-Jian Huang,Xiao-Qi Zhang,Jing-Jing Yang,Jun-Fang Gong,Mao-Ping Song
Dalton Transactions Pub Date : 05/03/2022 00:00:00 , DOI:10.1039/D2DT01078J
Abstract

A series of new chiral PCN pincer Pd(II) complexes 3a–l with aryl-based (phosphine)-(imidazoline) ligands were conveniently synthesized from readily available starting materials with the key step being phosphination/C–H palladation reaction. All of the new complexes were characterized by 1H NMR, 13C{1H} NMR, 31P{1H} NMR, and elemental analysis. In addition, the molecular structures of complexes 3c, 3e, 3i, and 3k have been determined by X-ray single crystal diffraction analysis. The potential of the obtained pincer Pd(II) complexes in catalytic enantioselective hydrophosphination reaction was examined. With a loading of 5 mol% and in the presence of a KOAc base, complex 3e acted as an active and stereoselective catalyst for hydrophosphination of various 2-alkenoylpyridines with diphenylphosphine, providing optically active pyridine-containing phosphine derivatives with structural diversity in excellent yields with moderate to good enantioselectivities (up to >99 yield and 87% ee).

Graphical abstract: Chiral (phosphine)-(imidazoline) PCN pincer palladium(ii) complexes: synthesis and application in asymmetric hydrophosphination of 2-alkenoylpyridines with diphenylphosphine
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