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Reference: Pearson, Mark, (1992). Organometallic reagents for catalytic cross-coupling. DPhil. University of Oxford.Citable link to this page:

 

Organometallic reagents for catalytic cross-coupling

Abstract: Phosphine complexes of nickel and palladium provide the best catalysts for thehomogeneous catalysed carbon-carbon bond forming reaction between an organometallicnucleophile and an organic electrophile. Use of a homochiral ligand on the catalyst can leadto stereoselectivity in the cross-coupling reaction, with high ee's of coupled product beingobtained. The processes of selectivity in the transmetalation step of the catalytic cycle havenot been elucidated and the initial aim of the project was to study these processes.Initial experiments using organotin derivatives as the organometallic nucleophilehighlighted the problems of selectivity and the forcing conditions needed in the attemptedtransfer of a benzyl group from the tin to the palladium catalyst. The compounds [8-(dimethylamino)-1-naphthyl]methyldiphenyltin (60) and [2-((dimethylamino)methyl)phenyl]methyldiphenyltin (70) were prepared and their reactivity in the palladium catalysedcross-coupling with 2-furoyl chloride, to give 2-benzoylfuran, was investigated. Thesemolecules were found to undergo facilitated transfer of a phenyl group compared to transferfrom control molecules. The effect was tested and attributed to the internal nucleophilicattack at the tin atom by the lone pair on the nitrogen atom. The compound [2-((dimethylamino)methyl)-3-trimethylsilylphenyl]methyldiphenyltin (79) was prepared totest the effects of steric buttressing within the molecule, but was found to be of the sameorder of magnitude of reactivity as (60) and (70). All three molecules showed a reactivity ofat least an order of magnitude greater than control compounds. The effect did not proveapplicable to the transfer of a benzyl group or in other coupling reactions. The effect ofpalladium ligation was tested and the ligand triphenyl arsine found to increase the rate of thecoupling reaction. The two facilitating processes were found to work in a co-operativefashion, giving a rate enhancement of ca. one hundredfold over control reactions.The nickel catalysed cross-coupling of α-substituted sp3 hybridised Grignardreagents with allylic esters was attempted, but proved unsuccessful. Stoichiometricreactions with nickel complexes were also found to be unsatisfactory in yielding coupledproducts.The synthesis of α-substituted diorganozinc reagents was attempted, but furnishedonly homocoupled products. The reaction of dibenzylzinc with aldehydes was found toproceed in the absence of catalyst, highlighting the reactivity of a benzylzinc moiety.

Type of Award:DPhil Level of Award:Doctoral Awarding Institution: University of Oxford Notes:This thesis was digitised thanks to the generosity of Dr Leonard Polonsky.

Contributors

Brown, John M.More by this contributor

RoleSupervisor

 

Dr. John BrownMore by this contributor

RoleSupervisor

 Bibliographic Details

Issue Date: 1992Identifiers

Urn: uuid:c5eea9a0-8f0c-46bf-a1ea-28a40b79546d

Source identifier: 603851238 Item Description

Type: Thesis;

Language: eng Subjects: Organometallic compounds Synthesis Nickel catalysts Palladium catalysts Tiny URL: td:603851238

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Autor: Pearson, Mark - institutionUniversity of Oxford facultyMathematical and Physical Sciences Division - - - - Contributors Brown, Jo

Fuente: https://ora.ox.ac.uk/objects/uuid:c5eea9a0-8f0c-46bf-a1ea-28a40b79546d



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