modes [2, 3, 5]. However, after the addition of acid, a dication forms, exhibiting
weak diatropic properties consistent with the 5
00 -H 2
2+ electronic structure.
Macrocycle 5 is puckered, acquiring a canted m-phenylene conformation with
respect to the N 3 plane. Characteristically, the
1 H NMR spectra of meso-tetraaryl-mbenziporphyrin 2 reflect features of an effectively planar structure indicating the
conformational equilibrium between two energetically equivalent conformers, differentiated by the direction of the phenylene ring canting [56]. m-Benziporphyrin
5 easily undergoes a conversion to phlorin 19 as a result of water, alcohol, or
dihydrogen additions (Scheme 8) [2].
Using the [3 + 1] methodology, 24-hetero-m-benziporphyrins, belonging to the
β-substituted or meso-substituted series, were obtained with heteroatoms: oxygen or
sulfur [57, 58]. Their diprotonation converts nonaromatic 24-hetero-mbenziporphyrins into the dicationic diatropic species.
2.2 m-Benziporphodimethenes
R 1
R 1
R 3
R 3
R 2
R 2
5
5'-H 2
2+
5"-H 2
2+
H
+
H
N
NH
HN
Ar
Ar
Ar
Ar
H
N
NH
HN
Ar
Ar
Ar
Ar
H
N
N
N
Ar
Ar
Ar
Ar
Scheme 7 Protonation of meso-substituted m-benziporphyrin 5
H
N
N
N
Ar
Ar
Ar
Ar
N
NH
HN
Ar
Ar
Ar
Ar
R
alcohol,
acid or
hydride
R= OH, OMe, H
5
19
Scheme 8 m-Benziphlorin 19 formation
188
K. Hurej and L. Latos-Grażyński