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Pd-Catalyzed Transfer Hydrogenolysis of Primary, Secondary, and Tertiary Benzylic Alcohols by Formic Acid: A Mechanistic Study
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Syntetisk organisk kemi.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Fysikalisk-organisk kemi.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för kemi - BMC, Syntetisk organisk kemi.
2013 (Engelska)Ingår i: ACS Catalysis, ISSN 2155-5435, Vol. 3, nr 4, s. 635-642Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
2013. Vol. 3, nr 4, s. 635-642
Nationell ämneskategori
Naturvetenskap
Identifikatorer
URN: urn:nbn:se:uu:diva-196658DOI: 10.1021/cs300785rISI: 000317328000024OAI: oai:DiVA.org:uu-196658DiVA, id: diva2:610665
Forskningsfinansiär
EnergimyndighetenTillgänglig från: 2013-03-12 Skapad: 2013-03-12 Senast uppdaterad: 2014-01-23Bibliografiskt granskad
Ingår i avhandling
1. Palladium-Catalyzed Nucleophilic Substitution of Alcohols: Mechanistic Studies and Synthetic Applications
Öppna denna publikation i ny flik eller fönster >>Palladium-Catalyzed Nucleophilic Substitution of Alcohols: Mechanistic Studies and Synthetic Applications
2013 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2013. s. 63
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1092
Nyckelord
palladium, nucleophilic substitution, mechanism
Nationell ämneskategori
Organisk kemi
Forskningsämne
Organisk kemi
Identifikatorer
urn:nbn:se:uu:diva-209541 (URN)978-91-554-8785-0 (ISBN)
Disputation
2013-12-09, B21, Husargatan 3, Uppsala, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2013-11-18 Skapad: 2013-10-21 Senast uppdaterad: 2014-09-11

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