| Development of 4,4'-substituted-XylBINAP ligands for highly enantioselective hydrogenation of ketones. | |
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MedLine Citation:
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PMID: 15704949 Owner: NLM Status: PubMed-not-MEDLINE |
Abstract/OtherAbstract:
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[reaction: see text] A family of 4,4'-substituted-xylBINAPs was synthesized in multistep sequences and characterized by NMR spectroscopy and mass spectrometry. Ru(diphosphine)(diamine)Cl(2) complexes based on these 4,4'-substituted-xylBINAPs and chiral diamines (DPEN and DAIPEN) were synthesized by treatment of [(benzene)RuCl(2)](2) with 4,4'-substituted-xylBINAP followed by chiral diamine, and characterized by (1)H and (31)P NMR spectroscopy and mass spectrometry. These Ru complexes were used for asymmetric hydrogenation of aromatic ketones in a highly enantioselective manner with complete conversion. With 0.1% catalyst loading, complete conversion and enantioselectivity greater than 99% were obtained for most of the aromatic ketones examined. These Ru catalysts thus gave the highest ee for asymmetric hydrogenation of aromatic ketones among all of the catalysts reported in the literature. A single-crystal X-ray diffraction study of Ru[(R)-L(4)()][(R,R)-DPEN]Cl(2) indicated that the 4-methyl group of the naphthyl ring and the methyl groups of the two xylyl moieties form a fence on the opposite side of the DPEN ligand of the Ru center. These three methyl groups will have significant repulsive interactions with the bulky aryl ring of the hydrogen-bonded aromatic ketone in the disfavored transition state. These results support our hypothesis of combining dual modes of enantiocontrol (i.e., the substituents on 4,4'-positions of the binaphthyl framework and the methyl groups on the bis(xylyl)phosphino moieties) to achieve higher stereoselectivity in the hydrogenation of aromatic ketones. |
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Authors:
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Helen L Ngo; Wenbin Lin |
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Publication Detail:
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Type: Journal Article |
Journal Detail:
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Title: The Journal of organic chemistry Volume: 70 ISSN: 0022-3263 ISO Abbreviation: J. Org. Chem. Publication Date: 2005 Feb |
Date Detail:
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Created Date: 2005-02-11 Completed Date: 2005-05-11 Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 2985193R Medline TA: J Org Chem Country: United States |
Other Details:
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Languages: eng Pagination: 1177-87 Citation Subset: - |
Affiliation:
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Department of Chemistry, CB#3290, University of North Carolina, Chapel Hill, North Carolina 27599, USA. |
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From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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