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Influence of steric symmetry and electronic dissymmetry on the enantioselectivity in palladium-catalyzed allylic substitutions
KTH, Superseded Departments, Chemistry.
KTH, Superseded Departments, Chemistry.
KTH, Superseded Departments, Chemistry.
KTH, Superseded Departments, Chemistry.
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2003 (English)In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 68, no 8, 3258-3270 p.Article in journal (Refereed) Published
Abstract [en]

Chiral P,N-ligands with pseudo-C2 and pseudo-Cs symmetry based on chiral pyrrolidine and phospholane rings or on dinaphthatodihydroazepino and dinaphthatodihydrophosphepino moieties were prepared and assessed in the palladium-catalyzed allylic substitutions of allylic acetates. Higher selectivity was achieved with pseudo-C2-symmetric ligands based on the binaphthyl skeleton than with the analogous C2-symmetric P,P- and N,N-analogues. Pseudo-C2-type ligands had properties superior to those of pseudo-meso-type ligands when 1,3-diphenyl-2-propenyl acetate was used as a substrate, whereas the reverse situation was found for 3-cyclohexenyl acetate. Chirally flexible ligands, prepared by substitution of one of the rigid binaphthyl skeletons for a flexible biphenyl system, were found to induce chirality to the same extent as a 1:1 mixture of the rigid ligands.

Place, publisher, year, edition, pages
2003. Vol. 68, no 8, 3258-3270 p.
Keyword [en]
Catalysis, Mixtures, Palladium, Substitution reactions
National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-6327DOI: 10.1021/jo026889eISI: 000182280900035OAI: oai:DiVA.org:kth-6327DiVA: diva2:11011
Note
QC 20100920Available from: 2006-11-10 Created: 2006-11-10 Last updated: 2010-09-20Bibliographically approved
In thesis
1. Flexibility – a tool for chirality control in asymmetric catalysis
Open this publication in new window or tab >>Flexibility – a tool for chirality control in asymmetric catalysis
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis deals with the design and synthesis of ligands for asymmetric catalysis: palladium catalyzed allylic alkylations, and rho-dium and iridium catalyzed hydrogenations of olefins.

Chirally flexible phosphepine ligands based on biphenyl were synthesized and their properties were studied. The rotation barrier for configurationally flexible phosphepines was determined by NMR spectroscopy. The ratio of the atropisomers was shown to depend on the group bound to phosphorus. Only complexes with two homochiral ligands bound to the metal center were observed upon complexation with Rh(I). It was shown that one diastereomer of the flexible ligand exhibits higher activity but lower selectivity than its diastereomer in the rhodium catalyzed hydrogenation of methyl alfa-acetamidocinnamate. These ligands were also tested in nickel catalyzed silabora-tions.

Chiral P,N-ligands with pseudo-C2 and pseudo-CS symmetry based on pyrrolidines-phospholanes or azepines-phosphepines were synthesized and studied in palladium catalyzed allylic alkylations. Semi-flexible azepine-phosphepine based ligands were prepared and their ability to adopt pseudo-C2 or pseudo-CS symmetry depending on the substrate in allylic alkylations was studied. It was shown on model allyl systems with flexible N,N-ligands that the ligand prefers CS-symmetry in compexes with anti-anti as well as syn-syn allyl moieties, but that for the latter type of complexes, according to computations, the configuration of the ligand is R*,R* in the olefin complexes formed after addition of a nucleophile to the allylic group.

A preliminary investigation of the possibilities to use a su-pramolecular approach for the preparation of P,N-ligands with pseudo-C2 and pseudo-S symmetry was made. An N,N-ligand with C2 symmetry was prepared and its activity in palladium catalyzed ally-lic alkylation was studied.

Pyridine-based P,N-ligands were tested in iridium catalyzed hy-drogenations of unfunctionalized olefins with good activities and se-lectivities. In order to attempt to improve the selectivity, ligands with a chirally flexible phosphepine fragment were prepared and applied in catalysis with promising results.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 58 p.
Series
Trita-IOK, ISSN 1100-7974 ; 2006:104
Keyword
flexibility, symmetry, dissymmetry, asymmetric catalysis, chiral ligands, pseudo-C2, pseudo-CS, conformational study, rotation barrier, pyrrolidines, phospholanes, azepines, phosphepines, supramolecular, hydrogenation, allylic alkylation, silaboration, palladium, rhodium, nickel, platinum, iridium.
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-4166 (URN)91-7178-491-8 (ISBN)
Public defence
2006-11-27, F3, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100929Available from: 2006-11-10 Created: 2006-11-10 Last updated: 2010-09-29Bibliographically approved

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