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Silaborations of Unsaturated Compounds
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
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 [en]
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: urn:nbn:se:kth:diva-9440ISBN: 978-91-7415-151-0 (print)OAI: oai:DiVA.org:kth-9440DiVA: diva2:114011
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: 2010-09-24Bibliographically approved
List of papers
1. Enantioselective Platinum-Catalyzed Silicon-Boron Addition to 1,3-Cyclohexadiene
Open this publication in new window or tab >>Enantioselective Platinum-Catalyzed Silicon-Boron Addition to 1,3-Cyclohexadiene
2005 (English)In: Advanced Synthesis and Catalysis, ISSN 1615-4150, E-ISSN 1615-4169, Vol. 347, no 6, 749-753 p.Article in journal (Refereed) Published
Abstract [en]

Silaboration of 1,3-cyclohexadiene in the presence of Pt(acac)(2), DIBALH, and a phosphoramidite prepared from (S)-1,1'-bi-2-naphthol and diisopropylamine led to (1R,4S)-1-(dimethylphenylsilyl)4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2-cyclohexene with 70% ee. Chiral catalysts based on Ni gave no or essentially racemic product, whereas complexes containing Pd were inactive.

 

 

 

 

Place, publisher, year, edition, pages
Weinheim: Wiley-VCH, 2005
Keyword
asymmetric catalysis; dienes; enantioselective; platinum; silaboration
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-9389 (URN)10.1002/adsc.200505016 (DOI)000229345400003 ()2-s2.0-20044378514 (Scopus ID)
Note
QC 20100727Available from: 2008-11-03 Created: 2008-10-30 Last updated: 2010-07-27Bibliographically approved
2. Enantioselective silicon-boron additions to cyclic 1,3-dienes catalyzed by the platinum group metal complexes
Open this publication in new window or tab >>Enantioselective silicon-boron additions to cyclic 1,3-dienes catalyzed by the platinum group metal complexes
Show others...
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
Keyword
Silaboration; Interelement; Enantioselective; Diastereoselective; Catalysis
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-9391 (URN)10.1016/j.jorganchem.2008.08.029 (DOI)000259890300008 ()2-s2.0-53249121378 (Scopus ID)
Note
QC 20100727Available from: 2008-11-03 Created: 2008-10-30 Last updated: 2010-07-27Bibliographically approved
3. Ni-Catalyzed Si-B Addition to 1,3-Dienes: Disproportionation in Lieu of Silaboration
Open this publication in new window or tab >>Ni-Catalyzed Si-B Addition to 1,3-Dienes: Disproportionation in Lieu of Silaboration
2006 (English)In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 8, no 14, 2929-2932 p.Article in journal (Refereed) Published
Abstract [en]

Upon attempted silaboration of acyclic 1- and 1,4-substituted 1,3-dienes, a new disproportionation reaction was discovered, yielding 1:1 mixtures of allylsilanes and dienylboranes. It was demonstrated that, as a key step in this new catalytic process, hydrogen is being transferred from one diene moiety to another.

Place, publisher, year, edition, pages
American Chemical Society, 2006
Keyword
DOUBLE SILYLATION; ALKYNE INSERTION; COMPLEXES; ALKENES; CHEMISTRY; SILICON; DIENES; DIBORATION; BONDS
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-9393 (URN)10.1021/ol060765x (DOI)000238645300008 ()2-s2.0-33746602236 (Scopus ID)
Note
QC 20100727Available from: 2008-11-03 Created: 2008-10-30 Last updated: 2010-07-27Bibliographically approved
4. Silaborative Carbocyclization of 1,6-Enynes
Open this publication in new window or tab >>Silaborative Carbocyclization of 1,6-Enynes
(English)Manuscript (Other academic)
Abstract [en]

The silaboration of 1,6-enynes gives densely functionalized five-membered rings that offer promising reactivities for further synthetic manipulations. We have found that using silylborane 4 silaborative carbocyclization reactions proceed in good to excellent yields, giving the product as a single diastereomer. Attempts to extend this methodology to include terminally substituted enynes and developing asymmetric versions were largely unsuccessful. The vinylboronates formed were employed in Suzuki cross-coupling reactions with a range of aryl bromides, furnishing arylated product in good yields.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-9394 (URN)
Note
QC 20100924Available from: 2008-11-03 Created: 2008-10-30 Last updated: 2010-09-24Bibliographically approved
5. Rate and Mechanism of the Oxidative Addition of a Silylborane to Pt0 Complexes: Mechanism for the Pt-Catalyzed Silaboration of 1,3-Cyclohexadiene
Open this publication in new window or tab >>Rate and Mechanism of the Oxidative Addition of a Silylborane to Pt0 Complexes: Mechanism for the Pt-Catalyzed Silaboration of 1,3-Cyclohexadiene
2008 (English)In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-0682, no 27, 4236-4241 p.Article in journal (Refereed) Published
Abstract [en]

The chemical reduction of Pt(acac)(2) by DIBALH in the presence of phosphanes, which is used to generate active Pt-0 complexes in the Pt-catalyzed silaboration of cyclohexadiene by 2-(diinethylphenylsilyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (1) leading to the 1,4-silaborated product, was mimicked by the electrochemical reduction of Pt(acac)(2) in the presence of 2 equiv. of PR3 (R = Ph, nBu). The electrochemical reduction generates free acac anions and neutral Pt-0-(PR3)(2) complexes. The kinetics of the oxidative addition of bromobenzene (used first as a model molecule) and silylborane 1 to the Pt-0 complexes was investigated and the rate constants determined. Pt-0(PnBu(3))(2) is much more reactive than Pt-0(PPh3)(2) towards 1. From the electrochemical study, it emerges that the acac anions released in the reduction of Pt(acac)(2) do not coordinate to the Pt-0(PR3)(2) complexes. Consequently, the rate of the oxidative addition of 1 to Pt-0(PR3)(2), generated either by the electrochemical reduction or by the chemical reduction by DIBALH, is not affected by the acac anions and a posteriori not by aluminum cations. The oxidative addition and the further step of the catalytic cycle [insertion of the diene into the Pt-B bond of the Si-Pt-B complex generated in the oxidative addition, with formation of the eta(3)-allyl)Pt-Si complex] were monitored by NMR spectroscopy. Pt-0 and Pt-II complexes involved in the catalytic cycle were characterized. The oxidative addition is faster when the ligand is PMe2Ph relative to that obtained with PPh3, in agreement with the electrochemical data. No reductive elimination within the ((eta(3)-allyl))Pt-Si complex is observed when the ligand is PMe2Ph, whereas reactions in the presence of PPh3 proceeded to give the final product. As a consequence, PPh3 is a better ligand than PMe2Ph for the catalytic reaction, as observed experimentally.

Place, publisher, year, edition, pages
Weinheim: Wiley-VCH, 2008
Keyword
Platinum; Silaboration; Reaction mechanisms; Kinetics
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-9395 (URN)10.1002/ejic.200800285 (DOI)000259943900006 ()2-s2.0-53549134267 (Scopus ID)
Note
QC 20100727Available from: 2008-11-03 Created: 2008-10-30 Last updated: 2010-07-27Bibliographically approved

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