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Scheme 8.2
Schematic representation of metal controlled fixation of secondary peptide
structures.
dominating/only species, either if a mixture of ligand 15 and catechol (1 : 1) is used in the
coordination studies, or if the titanium(IV) unit is substituted by molybdenum(VI)dioxo
(Figure 8.16). In the latter case the metal binds two catechols, while the third
coordination site is already blocked by the two oxo ligands.
The Leu-Ala-Leu substituted dipyridine ligand
22 was prepared to form a metallama-
crocycle by coordination to the Pd(en) (en
ethylene diamine) unit. Indeed the 1 : 1
complex is obtained as the dominant species. However, the corresponding 2 : 2 and 3 : 3
complexes are also observed in significant amounts [39]. The same concept is used with
the bisterpyridine ligand 23 , which in the presence of iron(II) cleanly produces the metal-
lamacrocycle [ 23 Fe] (Figure 8.17) [40].
¼
Figure 8.16 Metal complexes in which a well defined Val-Val-Val loop-type structure is
enforced by the binding of the metal ion.
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