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Rate and Mechanism of the Oxidative Addition of a Silylborane to Pt0 Complexes: Mechanism for the Pt-Catalyzed Silaboration of 1,3-Cyclohexadiene
CNRS, Ecole Normale Super, Dept Chim.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.ORCID iD: 0000-0002-1743-7650
CNRS, Ecole Normale Super, Dept Chim.
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. no 27, 4236-4241 p.
Keyword [en]
Platinum; Silaboration; Reaction mechanisms; Kinetics
National Category
Chemical Sciences
URN: urn:nbn:se:kth:diva-9395DOI: 10.1002/ejic.200800285ISI: 000259943900006ScopusID: 2-s2.0-53549134267OAI: diva2:113841
QC 20100727Available from: 2008-11-03 Created: 2008-10-30 Last updated: 2010-07-27Bibliographically 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.
Trita-CHE-Report, ISSN 1654-1081 ; 2008:67
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
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)
QC 20100924Available from: 2008-11-04 Created: 2008-11-04 Last updated: 2010-09-24Bibliographically approved

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