Abstract:A non-catalytic condensation of Ni β-aminonorcorrole with aryl aldehydes is shown to produce a family of pyrromethane dimers that undergo deaminative cyclization to yield pyridine-fused bis(norcorrole)s comprising two antiaromatic macrocycles communicating by an aromatic moiety. The new compounds were characterized by spectroscopic, structural, and electrochemical methods supported by DFT calculations, all of which revealed unexpected antiaromaticity enhancement in the fused system.
“…2a), and we have already reported the synthesis of a stable norcorrole Ni(II) complex 18 . The observed reactivity, optical properties, and electrochemical properties of this complex are markedly different from those of conventional aromatic porphyrins 19,20 .Fig. 2Norcorroles and a norcorrole cyclophane.…”
Understanding of interactions among molecules is essential to elucidate the binding of pharmaceuticals on receptors, the mechanism of protein folding and self-assembling of organic molecules. While interactions between two aromatic molecules have been examined extensively, little is known about the interactions between two antiaromatic molecules. Theoretical investigations have predicted that antiaromatic molecules should be stabilized when they stack with each other by attractive intermolecular interactions. Here, we report the synthesis of a cyclophane, in which two antiaromatic porphyrin moieties adopt a stacked face-to-face geometry with a distance shorter than the sum of the van der Waals radii of the atoms involved. The aromaticity in this cyclophane has been examined experimentally and theoretically. This cyclophane exhibits three-dimensional spatial current channels between the two subunits, which corroborates the existence of attractive interactions between two antiaromatic π-systems.
“…2a), and we have already reported the synthesis of a stable norcorrole Ni(II) complex 18 . The observed reactivity, optical properties, and electrochemical properties of this complex are markedly different from those of conventional aromatic porphyrins 19,20 .Fig. 2Norcorroles and a norcorrole cyclophane.…”
Understanding of interactions among molecules is essential to elucidate the binding of pharmaceuticals on receptors, the mechanism of protein folding and self-assembling of organic molecules. While interactions between two aromatic molecules have been examined extensively, little is known about the interactions between two antiaromatic molecules. Theoretical investigations have predicted that antiaromatic molecules should be stabilized when they stack with each other by attractive intermolecular interactions. Here, we report the synthesis of a cyclophane, in which two antiaromatic porphyrin moieties adopt a stacked face-to-face geometry with a distance shorter than the sum of the van der Waals radii of the atoms involved. The aromaticity in this cyclophane has been examined experimentally and theoretically. This cyclophane exhibits three-dimensional spatial current channels between the two subunits, which corroborates the existence of attractive interactions between two antiaromatic π-systems.
“…The UV/Vis/NIR absorption spectrum of 3 exhibited a significant red‐shift of the P 1 band by 2580 cm −1 from 2 , whereas the shift of the P 2 band was rather small (570 cm −1 , Figure ). Modest intensification of the S‐band region was also observed upon dimerization ,. In the case of meso,meso‐linked and β,β‐linked porphyrin dimers, similar absorption spectral changes from the corresponding monomers were explained in terms of the exciton coupling of two perpendicularly arranged transition dipole moments of the Soret bands .…”
5,15-Dioxaporphyrin was synthesized for the first time by a nucleophilic aromatic substitution reaction of a nickel bis(α,α'-dibromodipyrrin) complex with benzaldoxime, followed by an intramolecular annulation of the α-hydroxy-substituted intermediate. This unprecedented molecule is a 20π-electron antiaromatic system, in terms of Hückel's rule of aromaticity, because lone pair electrons of oxygen atoms are incorporated into the 18π-electron conjugated system of the porphyrin. A theoretical analysis based on the gauge-including magnetically induced current method confirmed its antiaromaticity and a dominant inner ring pathway for the ring current. The unique reactivity of 5,15-dioxaporphyrin forming a β,β-linked dimer upon oxidation was also revealed.
“…Column chromatography was carried out using silica gel 60 (200-300 mesh). The NMR spectra were recorded on a Bruker AV-II 500 MHz NMR spectrometer operating at 500 MHz for 1 H and at 125 MHz for 13 C; TMS was used as internal reference for 1 H and 13 C chemical shifts and CDCl 3 was the solvent. 2D experiments were performed using standard pulse sequences.…”
Section: Methodsmentioning
confidence: 99%
“…11 Trimethylsilyl cyanide (TMSCN) is a better source of cyanide than the alkali metal cyanides, being readily available, easy to handle and possessing high activity. 12 In continuation of our previous work on the synthesis of porphyrinoid derivatives, [13][14][15][16][17][18][19][20] in this paper we report the synthesis of 2-cyano-3-nitroporphyrin derivatives by the reaction of 2-nitroporphyrin with TMSCN in the presence of tetrabutylammonium fluoride (TBAF) in tetrahydrofuran (THF) at room temperature (Scheme 1).…”
2-Cyano-3-nitroporphyrin derivatives were synthesised by the reaction of 2-nitroporphyrin with trimethylsilyl cyanide in the presence of tetrabutylammonium fluoride with moderate yields. The reaction took place regioselectively on the 3-position carbon of the porphyrins, which was confirmed by X-ray analysis.
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