Interaction of Biomimetic Oligomers with Metal Ions - Metallofoldamers: Supramolecular Architectures from Helicates to Biomimetics - page 389

Figure 11.13 Molecular structures of (a) 6TCDA with two different chirality centers; the
diamine and the end-group and (b) the metallofoldamer 5TCDA from crystallographic coordi-
nates. Reprinted with permission from Ref. [30]. Copyright 2007 American Chemical Society.
Followed this work, the Fox group was interested to investigate other features that may
influence the absolute helicity of salen metallofoldamers. One such factor is the nature of
the internal chiral diamine. As discussed above and concluded from the work presented ear-
lier in this chapter, trans -cyclohexane-1,2-diamine is only a weak director of absolute helic-
ity in Ni-salen foldamers [30]. As trans -cyclohexane-1,2-diamine was the only chiral
diamine studied, it was difficult to deduce a general conclusion regarding the influence of
the diamine group on the helicity of metallofoldamers. Therefore, the Fox group wished to
understand how the structure of different chiral diamines would bias absolute helicity in
salen-based foldamers [33]. To this aim, three different chiral diamines, namely (1 R ,2 R )-
cyclopentanediamine ( CP-DA ), (1 S ,2 S )-1,2-diphenylethylenediamine ( DPE-DA ) and
(11 R ,12 R )-9,10-dihydro-9,10-ethanoanthracene-11,12 diamine ( DEA-DA ), were used to
prepare new salen oligomers (Figure 11.14), and the properties of the Ni-salen foldamers
Figure 11.14 Synthesis of Ni-salen foldamers from (1 R ,2 R )-cyclopentanediamine (CP-DA),
(1 S ,2 S )-1,2-diphenylethylenediamine (DPE-DA) and (11 R ,12 R )-9,10-dihydro-9,10-ethanoan-
thracene-11,12 diamine (DEA-DA). These foldamers have achiral end groups and the dia-
mines are the only source of central chirality [33].