A new class of versatile chiral-bridged atropisomeric diphosphine ligands: Remarkably efficient ligand syntheses and their applications in highly enantioselective hydrogenation reactions

Liqin Qiu, Fuk Yee Kwong, Jing Wu, Wai Har Lam, Shusun Chan, Wing Yiu Yu, Yue Ming Li, Rongwei Guo, Zhongyuan Zhou, Albert S.C. Chan

Research output: Journal article publicationJournal articleAcademic researchpeer-review

229 Citations (Scopus)

Abstract

A series of chiral diphosphine ligands denoted as PQ-Phos was prepared by atropdiastereoselective Ullmann coupling and ring-closure reactions. The Ullmann coupling reaction of the biaryl diphosphine dioxides is featured by highly efficient central-to-axial chirality transfer with diastereomeric excess >99%. This substrate-directed diastereomeric biaryl coupling reaction is unprecedented for the preparation of chiral diphosphine dioxides, and our method precludes the tedious resolution procedures usually required for preparing enantiomerically pure diphosphine ligands. The effect of chiral recognition was also revealed in a relevant asymmetric ring-closure reaction. The chiral tether bridging the two aryl units creates a conformationally rigid scaffold essential for enantiofacial differentiation; fine-tuning of the ligand scaffold (e.g., dihedral angles) can be achieved by varying the chain length of the chiral tether. The enantiomerically pure Ru- and Ir-PQ-Phos complexes have been prepared and applied to the catalytic enantioselective hydrogenations of α- and β-ketoesters (C=O bond reduction), 2-(6′-methoxy- 2′-naphthyl)-propenoic acid, alkyl-substituted β-dehydroamino acids (C=C bond reduction), and N-heteroaromatic compounds (C=N bond reduction). An excellent level of enantioselection (up to 99.9% ee) has been attained for the catalytic reactions. In addition, the significant ligand dihedral angle effects on the Ir-catalyzed asymmetric hydrogenation of N-heteroaromatic compounds were also revealed.
Original languageEnglish
Pages (from-to)5955-5965
Number of pages11
JournalJournal of the American Chemical Society
Volume128
Issue number17
DOIs
Publication statusPublished - 3 May 2006

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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