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Pd-Catalyzed Transfer Hydrogenolysis of Primary, Secondary, and Tertiary Benzylic Alcohols by Formic Acid: A Mechanistic Study
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Synthetical Organic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Physical Organic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Synthetical Organic Chemistry.
2013 (English)In: ACS Catalysis, ISSN 2155-5435, Vol. 3, no 4, 635-642 p.Article in journal (Refereed) Published
Abstract [en]

A palladium-catalyzed transfer hydrogenolysis of primary, secondary, and tertiary benzylic alcohols by formic acid has been developed and studied. The product hydrocarbons were obtained in excellent yields from bothsecondary and tertiary benzylic alcohols and in good yields for primary benzylicalcohols. The rate of disappearance of 1-phenylethanol (1) follows zero-order dependence in 1 and first-order dependence in formic acid and palladium. Catalytic amounts of base inhibit a competing disproportionation reaction ofalcohol to alkane and ketone, and an optimum was obtained when 5 equiv ofbase to palladium was used Deuterium kinetic isotope studies for the transferhydrogenolysis reveal individual isotope effects for the hydridic position (k(CHOH)/k(CDOH) = 2.26 +/- 0.24) and the protic position (k(CHOH)/k(CHOD) = 0.62 +/- 0.06) of the formic acid. Simultaneous deuteration in both positions offormic acid gave a combined isotope effect of (k(CHOH)/k(CDOD) = 1.41 +/- 0.11). We propose a mechanism involving the following steps: a competitive inhibition of the open palladium site by adsorption of the formate anion to generate formato-palladium species, followed by a reversible protonation and arate-limiting hydride transfer to obtain the active palladium with chemisorbed hydrogen that performs the hydrogenolysis of the alcohol in a fast reaction step.

Place, publisher, year, edition, pages
2013. Vol. 3, no 4, 635-642 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-196658DOI: 10.1021/cs300785rISI: 000317328000024OAI: oai:DiVA.org:uu-196658DiVA: diva2:610665
Funder
The Swedish Energy Agency
Available from: 2013-03-12 Created: 2013-03-12 Last updated: 2014-01-23Bibliographically approved
In thesis
1. Palladium-Catalyzed Nucleophilic Substitution of Alcohols: Mechanistic Studies and Synthetic Applications
Open this publication in new window or tab >>Palladium-Catalyzed Nucleophilic Substitution of Alcohols: Mechanistic Studies and Synthetic Applications
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with the palladium-catalyzed nucleophilic substitution of π-activated alcohols in which the C–O bond of a non-manipulated hydroxyl group is cleaved. The thesis is divided in two chapters describing two different catalytic systems.

Chapter 2 describes a heterogeneous palladium-catalyzed transfer hydrogenolysis of primary, secondary, and tertiary benzylic alcohols to generate the corresponding aromatic hydrocarbons using formic acid as the hydrogen donor. A detailed mechanistic investigation of this reaction has been conducted that establish the kinetic order of each reaction component and also the deuterium kinetic isotope effects. This data provide a mechanistic picture that the hydride transfer from formic acid to palladium, and not the C–O bond cleavage, is involved in the rate-determining step and that a catalytic amount of a base promotes the transfer hydrogenolysis.

Chapter 3 describes the development, mechanistic studies and synthetic scope of a homogeneous palladium-catalyzed amination of allylic alcohols. Isolation of the catalyst precursor and equilibrium studies of the palladium and π-acidic triphenylphosphite ligand show unique properties of this catalytic system. Stereochemical, kinetic, and kinetic isotope studies have been performed to provide insight into the mechanism of C–O bond cleavage of allylic alcohol and C–N bond formation catalyzed by the palladium complex. Interestingly, both O–H and C–O bond cleavages are involved in rate-determining steps.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 63 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1092
Keyword
palladium, nucleophilic substitution, mechanism
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-209541 (URN)978-91-554-8785-0 (ISBN)
Public defence
2013-12-09, B21, Husargatan 3, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2013-11-18 Created: 2013-10-21 Last updated: 2014-09-11

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Sawadjoon, SupapornLundstedt, AnnaSamec, Joseph

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