6-Azahemiporphycene: a new member of the porphyrinoid family.
The reaction of 5,10,15-triarylcorrole with 4-amino-4H-1,2,4-triazole provides another example of corrole ring expansion to give the corresponding 6-azahemiporphycene, a novel porphyrin analogue. The facile oxidation of the corrole ring is a required step for the ring expansion and for this reason the reaction fails in the case of corroles bearing meso-phenyl groups carrying electron-withdrawing substituents. Steric requirements also limited the scope of the reaction, which is not successful in the case of 2,6-disubstituted meso-aryl corroles. The occurrence of an initial oxidation is further supported by formation of the 6-azahemiporphycene derivative when the reaction is carried out under the same conditions, using a 5- or a 10-isocorrole as starting material. (1)H NMR spectra and X-ray crystal characterization of 6-azahemiporphycene evidenced the presence of an intramolecular N-H...N hydrogen bond in the inner core of the macrocycle, while photophysical characterization confirmed the aromatic character of the novel macrocycle, showing an intense Soret-like band around 410 nm in the absorption spectrum. The fluorescence emission is very modest, and 6-azahemiporphycene showed higher photostability than the corresponding corrole species. Different metal complexes of 6-azahemiporphycene were prepared following synthetic protocols usually exploited for the preparation of metalloporphyrins, demonstrating good coordination properties for the macrocycle. Both the free-base and metal derivatives were characterized by cyclic voltammetry and spectroelectrochemistry in dichloromethane and benzonitrile. To further detail the behavior of this novel macrocycle, density functional theory (DFT) calculations were carried out on the basic structure of 6-azahemiporphycene with the aim of assessing aromaticity and tautomerism, as well as calculating its stability with respect to the 5-aza isomer.
Department of Chemical Science and Technologies, University of Rome Tor Vergata, Via della Ricerca Scientifica 1, 00133 Rome, Italy.
Federica
F
Mandoj
Sara
S
Nardis
Giuseppe
G
Pomarico
Manuela
M
Stefanelli
Luca
L
Schiaffino
Gianfranco
G
Ercolani
Luca
L
Prodi
Damiano
D
Genovese
Nelsi
N
Zaccheroni
Frank R
FR
Fronczek
Kevin M
KM
Smith
Xiao
X
Xiao
Jing
J
Shen
Karl M
KM
Kadish
Roberto
R
Paolesse
D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011166:Porphyrins / Q000737:chemistry* / Q000145:classification; D011725:Pyridines / Q000737:chemistry*; D011789:Quantum Theory
C546073:6-azahemiporphycene; D011166:Porphyrins; D011725:Pyridines; C431863:corrole