Nitration of Norcorrolatonickel(II): First Observation of a Diatropic Current in a System Comprising a Norcorrole Ring

Abstract

A one-pot reaction of 5,14-bis(mesityl)-norcorrolatonickel(II) with isoamyl nitrite under mild reaction conditions resulted in the consecutive formation of 3-nitro-, 3,12-dinitro- and 3,16-dinitro-, 3,7,12-trinitro-, and 3,7,12,16-tetranitro-norcorrolatonickel(II) in 50-80% yield. The substituted macrocycles retained their antiaromatic character. The observed regioselectivity of the substitution was analyzed by comparing the relative energies of the DFT energy-optimized models of the radical or arenium cationic intermediates that can be formed upon reaction with NO2. The nitrated systems were characterized by high-resolution mass spectrometry, NMR and UV/Vis spectroscopy, X-ray diffraction analysis, cyclic voltammetry, and DFT calculations. A significant and systematic cathodic shift of the redox couples was observed to correlate with an increasing number of the NO2 group. A decrease of the LUMO energies in the tri- and tetra-nitrated products stabilizes mono- and bis-reduced complexes of these ligands. The reduction takes place on the macrocycle rather than on the metal ion leading to the consecutive formation of stable paramagnetic monoanion radicals and water-soluble diamagnetic dianions with an aromatic character, which were revealed by ESR and (1)H NMR measurements, respectively. The electronic structures of the reduced forms were analyzed by extensive TD-DFT calculations.

Reversible Carbon–Carbon Bond Breaking and Spin Equilibria in Bis(pyrimidinenorcorrole)

“…Nickel(II) norcorrole 1 is ar ecently discovered 16-pelectron tetrapyrrolic porphyrinoid, which displays an antiaromatic character and areactivity quite distinct from that of aromatic oligopyrroles. [4][5][6] In an attempt to introduce an NH 2 group into 1,w ee mployed 4H-1,2,4-triazol-4-amine [7] in the presence of solid sodium hydroxide in THF (Scheme 1). The amination proceeded with the regioselectivity observed previously for cyanation [5c] and nitration [6b] providing 3aminonorcorrolatonickel(II) 2 in 28 %yield.…”

Pyridine‐Fused Bis(Norcorrole) through Hantzsch‐Type Cyclization: Enhancement of Antiaromaticity by an Aromatic Bridge

“…The average deviation from the mean plane defined by all non‐H atoms of the macrocycle is 0.10 Å with the corresponding out‐of‐plane displacements of Ni II atoms of 0.22 Å. The Ni−N distances range from 1.767(4) to 1.794(5) Å and are similar to those observed for monomers 1 – 3 . The mean planes of the macrocyclic subunits in 4 c are almost perpendicular to each other with a dihedral angle of ca.…”

“…Single crystal X‐ray diffraction analyses for 4 c confirmed their structures in the solid state (Figure A). Unlike the parent monomers 1 – 3 , wherein norcorrole rings were almost ideally planar, in dimer 4 c the macrocycles are slightly but noticeably bowl‐shaped . The average deviation from the mean plane defined by all non‐H atoms of the macrocycle is 0.10 Å with the corresponding out‐of‐plane displacements of Ni II atoms of 0.22 Å.…”

“…While direct amination of the norcorrole ring is a feasible reaction, it is insufficiently selective to be used for large‐scale preparation of aminonorcorrole 3 . In contrast, regioselective nitration of 1 with amyl nitrite followed by an efficient reduction of NO 2 group with tin chloride, turned out to be an efficient path to the monoaminated norcorrolatonickel(II).…”

“…It has been shown that norcorrolatonickel(II) 1 , a readily obtainable air‐stable antiaromatic 16‐π‐electron tetrapyrrolic porphyrinoid, can be effectively functionalized by means of diverse substitution, addition, insertion, or dimerization reactions. Amination of the macrocycle followed by oxidative annulation has been recently shown to be an effective way to fuse aromatic rings .…”