Synthesis of Functionalised Cobalt Sandwich Complexes for Application in Asymmetric Catalysis

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.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2014

Author dc:creator

• Cassar, Doyle

Language dc:language

en