Synthesis of Functionalised Cobalt Sandwich Complexes for Application in Asymmetric Catalysis

Cassar, Doyle (2014) Synthesis of Functionalised Cobalt Sandwich Complexes for Application in Asymmetric Catalysis. Doctoral thesis, University of East Anglia.

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    Abstract

    The reaction of cobalt sandwich complex (η5-(N,N-dimethylaminomethyl)cyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt with sodium tetrachloropalladate and N-acetyl-D-phenylalanine gave planar chiral palladacycle di-μ-chloridebis[(η5-(Sp)-2-(N,N-dimethylaminomethyl)cyclopentadienyl,1-C,3′-N)(η4-tetraphenylcyclobutadiene)cobalt]dipalladium in 92% ee, 64% yield. The enantioselective palladation methodology was subsequently applied to corresponding N,N-diethyl (82% ee, 39% yield) and pyrrolidinyl (>98% ee, 43% yield) cobalt sandwich complexes. The complex derived from the pyrrolidinyl ligand was tested as a catalyst in the allylic imidate rearrangement (up to 99 % ee), showcasing comparable reactivity and selectivity to that seen in literature examples. The diastereoselective palladation of a range of (η5-oxazolinylcyclopentadienyl-(4-tetraphenylcyclobutadiene)cobalt complexes was tested by reaction with palladium acetate. Acetate dimer di-μ-acetatobis[(η5-(S)-(Sp)-2-(2’-4’-methylcyclohexyl)oxazolinyl)cyclopentadienyl, 1-C, 3’-N)(η4-tetraphenylcyclobutadiene)cobalt(I)]dipalladium(II) precipitated as a single diasteroisomer from the reaction media and was tested as a catalyst in the allylic imidate rearrangement (80% ee).
    In addition, access to modified sandwich complexes was realised using the Friedel-Crafts reaction. Complex (η4-tetraphenylcyclobutadiene)(η5-carbomethoxycyclopentadienyl)cobalt underwent reaction with acid chlorides/aluminum chloride to give exclusively para-acylation. Reaction of unsymmetrical bis-aryl alkynes [PhCC(o-RC6H4), R = Me, iPr] with Na(C5H4CO2Me) and CoCl(PPh3)3 gave predominantly (η4-1,3-diaryl-2,4-diphenylcyclobutadiene)(η5-carbomethoxycyclopentadienyl)cobalt metallocenes (1,3-[trans] vs 1,2-[cis] selectivity up to 6:1). Friedel-Crafts reaction on the major isomers gave exclusively the para-acylation of the unsubstituted phenyl groups.

    Item Type: Thesis (Doctoral)
    Faculty \ School: Faculty of Science > School of Chemistry
    Depositing User: Mia Reeves
    Date Deposited: 19 Jun 2015 11:58
    Last Modified: 19 Jun 2015 11:58
    URI: https://ueaeprints.uea.ac.uk/id/eprint/53373
    DOI:

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