Control of Chiral Assemblies Through Hydrogen Bondings for Helical Architectures - Molecular Self-Assembly: Advances and Applications - page 79

structure based on intramolecular hydrogen bonds is obtained in the
2:1 trans palladium complex 10 composed of the ferrocene-dipeptide

conjugate bearing one heterochiral dipeptide chain (-D-Ala-L-Pro-

NH-2-Py) (Figs. 3.11 and 3.12b) [23]. An opposite helical molecular
assembly, a right-handed pseudo-helical molecular arrangement, is
also formed through intermolecular hydrogen bonds between the
NH of the Ala and the CO adjacent to the ferrocene unit (another
molecule) in the crystal packing of the ferrocene

7

(Fig. 3.13b).
Catalytic activities have been demonstrated by the introduction
of metal coordination sites into peptides [24]. Phosphine-containing
b

10

-turn ligands are used in asymmetric catalysis. The alkylation of
cyclopentenyl acetate with dimethylmalonate can be catalyzed in
a high enantiomeric excess (ee) with the -turn-derived palladium

phosphine complexes (Scheme 3.1) [24b,c,d]. The

b

b

-turn secondary

structure is critical for high selectivity.

O O

Pd-Ligand
2 mol% Pd
N , O -bis(trimethylsilyl)acetamide
TBAF

OAc

O O

MeO OMe P

+

O

H
N

MeO OMe

O

N H

H

O

i Pr

On support 95% yield, 88% ee THF solvent
In solution 91% yield, 95% ee THF solvent

NH

O

H

O Ph

H
N

N

NHBoc

O

P

Ligand

b

Scheme 3.1 Asymmetric reaction catalyzed by the -turn-derived

palladium phosphine complexes.

3.3 Chiral Assemblies of 2,6-

Pyridinedicarboxamides and Dipeptidyl
Urea

3.3.1 Chiral Assemblies of 2,6-Pyridinedicarboxamides

The introduction of dipeptide chains into the ferrocene scaffold
has been demonstrated to permit chirality organization through
the intramolecular interchain hydrogen bonding, in which a helical
molecular arrangement is achieved in the crystal packing. However,
the 2,6-pyridinedicarboxamide scaffold has also been exploited for