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

• Published in: Chemistry : a European journal 2016-03, Vol.22 (12), p.4231-4246
• Main Authors: Deng, Zhihong, Li, Xiaofang, Stępień, Marcin, Chmielewski, Piotr J.
• Format: Article
• Language: English
• Subjects: Cations; Chemistry; Coordination compounds; Correlation; Diamagnetism; Energy; Formations; High resolution; Intermediates; Ligands; Mass spectrometry; Mass spectroscopy; Mathematical models; Metals; nickel; Nitration; Nitrites; Nitrogen dioxide; NMR; norcorroles; Nuclear magnetic resonance; porphyrinoids; Radicals; Redox properties; Reduction; Reduction (metal working); Regioselectivity; Spectroscopic analysis; Spectroscopy; Voltammetry; X-ray diffraction; Yield
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201504584

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 1H NMR measurements, respectively. The electronic structures of the reduced forms were analyzed by extensive TD‐DFT calculations. Multiple nitration of an antiaromatic nickel(II) complex of norcorrole with isoamyl nitrite occurred under mild conditions and was shown to be highly regioselective. The NO2 groups shifted the optical spectra towards the red region and stabilized the reduced forms of the macrocycle, thus allowing preparation of blue, aromatic, water‐soluble dianions of the tri‐ and tetra‐nitrated species (see figure, Mes=mesityl).