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II
2
clip. This new clip was utilized
in the self-assembly of a neutral molecular rectangle
in the lines of the aforementioned Pt
13
using linear
dicarboxylate donor fumarate
12
(Scheme 9.6).
Scheme 9.6
Formation of
13
by [2 + 2] self-assembly of the Pd
II
2
-clip and
fumarate linker.
II
neutral
macrocycle obtained using Pd-O coordination bonding as the
driving force. Oxygen-based hard donors are usually expected to be
unsuitable for soft acid Pd
Rectangle
13
represents a very rare example of a Pd
II
owing to the weak bonding interaction
between them. However, the electrostatic interaction between the
anionic fumarate and Pd
II
played an important role to stabilize this
unique Pd-O bond, which directed neutral rectangle.
9.2.3.1
Synthesis and Characterization of Neutral Molecular
Rectangles
Generally, oxygen-based hard donors are expected to be unsuitable
for soft acid like Pd
II
II
-O
coordination but the electrostatic interaction between the anionic
fumarate and Pd
. However, in this case it is not the Pd
II
that acts as the driving force for the formation
of the macrocyclic rectangle (
13
). When a methanolic solution of
3
was reacted with an aqueous solution of equimolar amount of Na
-
2
fumarate,
was formed as a fluorescent yellow precipitate in a
few minutes in almost quantitative yield.
13
A single peak appeared in
31
the
P NMR spectrum of the yellow precipitate in CDCl
at
δ
17.31
3
ppm shifted 1.85 ppm upfield relative to
3
, indicating the formation
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