2.1.2 meso-Tetraaryl-m-Benziporphyrin
R
R
R
R
meso-Tetraaryl-m-benziporphyrin 5 was obtained (2001) using the stochastic
method [2]. The synthesis involved the condensation of dicarbinol 18, formed
from isophthalaldehyde 17, with pyrrole and the corresponding aryl aldehyde
(Scheme 6). The choice of meso-aryl substituents determined the yield, which
oscillated in the 15–17% range. The syntheses of derivatives substituted at the
external m-phenylene position were subsequently reported [55].
meso-Tetraaryl-m-benziporphyrin 5, similarly as the β-substituted contender 16,
displays the
1 H NMR pattern, which is characteristic of nonaromatic porphyrinoids.
The m-phenylene units preserve a benzene-like electronic structure, being efficiently
isolated from the π-electron delocalization of the accompanying tripyrrolic brace
(Scheme 7). Thus, the absence of macrocyclic aromaticity in m-benziporphyrins
reflects a mismatch between the porphyrin-like and benzene-like π-delocalization
H
N
N
N
TFA
H
N
NH
HN
H
N
NH
HN
16'-H 2
2+
16
16''-H 2
2+
Scheme 5 Protonation of β-substituted m-benziporphyrin 16
OHC
CHO PhMgBr
OH
Ph
Ph
OH
pirol,
ArCHO,
BF 3
. Et 2 O
5
H
N
N
N
Ph
Ar
Ph
Ar
18
17
Scheme 6 Synthesis of meso-tetraaryl-m-benziporphyrin 5
A Pincer Motif Etched into a meta-Benziporphyrin Frame
187
R
R
R
R
meso-Tetraaryl-m-benziporphyrin 5 was obtained (2001) using the stochastic
method [2]. The synthesis involved the condensation of dicarbinol 18, formed
from isophthalaldehyde 17, with pyrrole and the corresponding aryl aldehyde
(Scheme 6). The choice of meso-aryl substituents determined the yield, which
oscillated in the 15–17% range. The syntheses of derivatives substituted at the
external m-phenylene position were subsequently reported [55].
meso-Tetraaryl-m-benziporphyrin 5, similarly as the β-substituted contender 16,
displays the
1 H NMR pattern, which is characteristic of nonaromatic porphyrinoids.
The m-phenylene units preserve a benzene-like electronic structure, being efficiently
isolated from the π-electron delocalization of the accompanying tripyrrolic brace
(Scheme 7). Thus, the absence of macrocyclic aromaticity in m-benziporphyrins
reflects a mismatch between the porphyrin-like and benzene-like π-delocalization
H
N
N
N
TFA
H
N
NH
HN
H
N
NH
HN
16'-H 2
2+
16
16''-H 2
2+
Scheme 5 Protonation of β-substituted m-benziporphyrin 16
OHC
CHO PhMgBr
OH
Ph
Ph
OH
pirol,
ArCHO,
BF 3
. Et 2 O
5
H
N
N
N
Ph
Ar
Ph
Ar
18
17
Scheme 6 Synthesis of meso-tetraaryl-m-benziporphyrin 5
A Pincer Motif Etched into a meta-Benziporphyrin Frame
187