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Enantioselective silicon-boron additions to cyclic 1,3-dienes catalyzed by the platinum group metal complexes
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
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2008 (English)In: Journal of Organometallic Chemistry, ISSN 0022-328X, E-ISSN 1872-8561, Vol. 693, no 23, 3519-3526 p.Article in journal (Refereed) Published
Abstract [en]

Silaborations of 1,3-cyclohexadiene and 1,3-cycloheptadiene were achieved using catalysts prepared from different combinations of phosphorus ligands and group 10 metal compounds. For the six-membered compound, 1,4-adducts with up to 82% ee were obtained employing Pt(0) and phosphoramidite ligands. For the seven-membered diene optimal conditions were found using catalysts based on Ni(0), but the highest selectivity observed was merely 22% ee. No improvement of the chiral induction was obtained using chiral silylboranes in combination with chiral phosphoramidite ligands in the additions to 1,3-cyclohexadiene. The adduct obtained from cyclohexadiene was used in allylborations of aldehydes under microwave irradiation to produce homoallylic alcohols with moderate to good diastereoselectivity.

Place, publisher, year, edition, pages
Elsevier B. V. , 2008. Vol. 693, no 23, 3519-3526 p.
Keyword [en]
Silaboration; Interelement; Enantioselective; Diastereoselective; Catalysis
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-9391DOI: 10.1016/j.jorganchem.2008.08.029ISI: 000259890300008Scopus ID: 2-s2.0-53249121378OAI: oai:DiVA.org:kth-9391DiVA: diva2:113837
Note
QC 20100727Available from: 2008-11-03 Created: 2008-10-30 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Silaborations of Unsaturated Compounds
Open this publication in new window or tab >>Silaborations of Unsaturated Compounds
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis deals with the development of transition metal-catalyzed silaborations of 1,3-dienes and 1,6-enynes.

The first part of the thesis describes the development of the enantioselective 1,4-silaboration of 1,3-cyclohexadiene. A number of chiral metal-ligand complexes were evaluated. Up to 82% enantiomeric excess was obtained using a catalyst system derived from Pt(acac)2 and a phosphoramidite ligand. The product formed was employed in allylborations of aldehydes, giving homo-allylic alcohols in good yields with good to moderate diastereoselectivity. In attempts to widen the scope of silaborations to include acyclic, terminally substituted 1,3-dienes, products from H-B exchange with, and H-Si addition to, the dienes were obtained.

The second part describes the development of silaborative carbocyclization of 1,6-enynes. A Pd N-heterocylic carbene complex was found to be effective for the silaborative carbocyclization of unsubstituted enynes, giving the products in good to excellent yields. Employing terminally substituted enynes resulted in low or no yields.

The last part describes investigations into the reaction mechanisms of the processes developed in the first part. It was found that the silylborane undergoes oxidative addition to a Pt(0) complex generated from Pt(acac)2 and DIBALH. After insertion of 1,3-cyclohexadiene into the Pt-B bond a π-allyl complex was observed experimentally. In the addition of silylborane to acyclic, terminally substituted, 1,3-dienes it was shown by deuterium labeling experiments that one diene loses a hydride via H-B exchange and that this hydride is then added to another diene via H-Si addition. A reaction mechanism was proposed for this process.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 53 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:67
Keyword
allylboration, bismetallation, boron, carbocyclization, catalysis, 1, 3-diene, enantioselective, 1, 6-enyne, interelement, N-heterocyclic carbene, nickel, palladium, phosphine, phosphoramidite, platinum, reaction mechanism, silaboration, silicon, silylborane, stereoselective
National Category
Other Basic Medicine
Identifiers
urn:nbn:se:kth:diva-9440 (URN)978-91-7415-151-0 (ISBN)
Public defence
2008-11-21, D2, KTH, Lindstedtsvägen 5, Stockholm, 10:15 (Swedish)
Opponent
Supervisors
Note
QC 20100924Available from: 2008-11-04 Created: 2008-11-04 Last updated: 2018-01-13Bibliographically approved
2. 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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