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Chiral Bisphosphinites For Asymmetric Catalysis

Electronic Theses of Indian Institute of Science

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Field Value
 
Title Chiral Bisphosphinites For Asymmetric Catalysis
 
Creator Sharma, Rakesh Kumar
 
Subject Catalysis
Chiral Bisphosphinites
Chiral Catalysts
Imines - Allylation
Aldehydes - Allylation
Styrene - Hydrosilylation
Asymmetric Allylic Alkylation
Bisphosphinite Complexes - Synthesis
Asymmetric Hydrosilylation
Asymmetric Catalysis
Physical Chemistry
 
Description Chiral bisphosphinites are well-documented alternatives for chiral bisphosphines as ligands that can be exploited in various asymmpetric syntheses. Particularly, vicinal biarylphophinite ligands give a seven membered chelate ring similar to the successful DIOP on coordination to the metal. RajanBabu and coworkers have described asymmetric bisphosphinites obtained by functionalization of sugars and have shown their utility in enantioselective hydrogenation, hydrovinylation and hydrocynation reactions. Despite the interesting reactions demonstrated by bisphosphinites, not much attention has been paid to their synthesis and catalysis. This is probably due to the known moisture and oxygen sensitivity that makes their use limited.
In the present thesis, a series of C1 an C2 symmetric bisphosphinite complexes of Pd(II) and Pt(II) have been synthesized directly from various naturally occurring chiral alcohols using a modified template method. A number of asymmetric catalytic reactions have been developed such as allylation of imines, allylation of aldehydes, allylic allylation, allylic alkylation, hydrosilylation of alkenes and regioselective allylation of oxiranes. Allylation of imines was carried out in essentially neutral conditions using Pd(II) catalysts and water was shown to accelerate the reaction. Interestingly acetic acid was required as a promoter in asymmetric allylation of cinnamaldehyde in the Pt(II) catalyzed reaction whereas water was a deterrent. Hydrosilylation reaction was carried out in solvent free conditions with high turnover numbers (.1000).
Ascorbic acid based complexes produced the highest enantioselectivity for the asymmetric allylic alkylation reaction (97 % ee) and hydrosilylation of styrene (98% ee). These enantioselectivity results are the best obtained using ligands directly prepared from natural products.
 
Contributor Samuelson, A G
 
Date 2010-07-21T09:21:19Z
2010-07-21T09:21:19Z
2010-07-21
2008-01
 
Type Thesis
 
Identifier http://etd.iisc.ernet.in/handle/2005/778
 
Language en_US
 
Relation G22323