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

Markus Albrecht; Rainer Nolting; Patrick Weis

doi:10.1055/s-2005-861865

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

Markus Albrecht*^a, Rainer Nolting^a, Patrick Weis^b
^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

Abstract

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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

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