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effect” between each set of acetylene moieties. The Lewis acid/base,
molecular square receptors incorporating acetylene groups, and
silver cations readily bind neutral guests such as pyridine, pyrazine,
phenazine, and dipyridyl ketone. The addition of the respective
guest to the 4-ethynylpyridine-based Pt
−
+
−
+
Pt/Ag
and Pt
Pd/Ag
receptors clearly shows host
-tweezer
effect” and the heteroatom coordination in dichloromethane at
room temperature results in the formation of corresponding ternary
complexes,
−
guest interaction via the “
π
31
1
25
(Scheme 10.2). Significant shift values in the
P,
H,
13
C NMR, and IR spectra supported the inclusion phenomenon.
4+
4TfO
-
PEt
3
4+
6TfO
-
PEt
3
PPh
2
PEt
3
M
PEt
3
P
Et
3
Pt
N
N
M
PEt
3
Ph
2
P
Pt
N
N
Ag
AgOTf
24
Ag
N
N
Et
3
P
M
N
Pt
Ph
2
P
PPh
2
Et
3
P
M
N
Pt
Ph
2
P
PPh
2
PEt
3
PEt
3
23
pyrazine
Guests
O
N
N
4+
6TfO
-
PEt
3
N
PPh
2
N
N
N
N
M
PEt
3
Ph
2
P
Pt
N
M = Pt, or Pd
Ag
N
N
Ag
N
Et
3
P
M
N
Pt
Ph
2
P
PPh
2
PEt
3
25
Scheme 10.2
binds electron-rich aromatic
guests in water with strikingly high affinity [76,77], which is ascribed
to the incorporation of an electron-deficient perfluorinated benzene
unit as well as the good fit of the cavity size. The nearly orthogonal
array of pyridines enables the formation of almost cube-shaped
cavity of dimension ca. 4
The palladacyclic molecular loop
26
×
×
4
6 Å. It was capable of binding 1,3,5-
trimethoxybenzene,
p
-dimethoxybenzene,
m
-dimethoxybenzene,
and
o
-dimethoxybenzene with association constants
K
= 2500,
a
−
2680, 1560, and 1300 M
1
, respectively. For larger guests, such
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