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Synthesis 2005(7): 1125-1135  
DOI: 10.1055/s-2005-861865
PAPER
© Georg Thieme Verlag Stuttgart · New York

Preparation of Amino Acid-Bridged Dicatechol Ligands for Dinuclear Titanium(IV) Complexes

Markus Albrecht*a, Rainer Noltinga, Patrick Weisb
a Institut für Organische Chemie der RWTH-Aachen, Professor-Pirlet-Straße 1, 52074 Aachen, Germany
Fax: +49(241)8092385; e-Mail: markus.albrecht@oc.rwth-aachen.de;
b Institut für Physikalische Chemie der Universität Karlsruhe, Fritz-Haber-Weg, 76128 Karlsruhe, Germany
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Publication History

Received 30 November 2004
Publication Date:
10 March 2005 (online)

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Abstract

Amino acid-bridged dicatechol ligands 2a-e-H4 were prepared by peptide coupling reactions. Under special conditions, an unusual BBr3-promoted amide to methyl ester transformation was observed for the asparagine and glutamine side chain functions. The ligands were used in coordination studies with titanium(IV) ions in the presence of an alkali metal carbonate. Double-stranded complexes Li2[(2a-e)2(OR)2Ti2] which have alcoholate coligands (R = CH3, C2H5, C3H5) bridging the metals were selectively formed with lithium counter cations. On the other hand, with potassium or sodium cations triple-stranded complexes M4[(2b,c,e)3Ti2] were obtained in addition to the double-stranded M2[(2b,c,e)2(OCH3)2Ti2] (M = Na, K).

Key words

peptide coupling - amino acid - ligands - metal complex - template effect