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Molecules 2018, 23(5), 1052;

Porphyrin Co(III)-Nitrene Radical Mediated Pathway for Synthesis of o-Aminoazobenzenes

Homogeneous, Supramolecular and Bio-Inspired Catalysis, van ‘t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
Author to whom correspondence should be addressed.
Academic Editor: John C. Walton
Received: 3 April 2018 / Revised: 25 April 2018 / Accepted: 26 April 2018 / Published: 1 May 2018
(This article belongs to the Special Issue Radical Chemistry)
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Azobenzenes are versatile compounds with a range of applications, including dyes and pigments, food additives, indicators, radical reaction initiators, molecular switches, etc. In this context, we report a general method for synthesizing o-aminoazobenzenes using the commercially available cobalt(II) tetraphenyl porphyrin [CoII(TPP)]. The net reaction is a formal dimerization of two phenyl azides with concomitant loss of two molecules of dinitrogen. The most commonly used methodology to synthesize azobenzenes is based on the initial diazotization of an aromatic primary amine at low temperatures, which then reacts with an electron rich aromatic nucleophile. As such, this limits the synthesis of azobenzenes with an amine functionality. In contrast, the method we report here relies heavily on the o-amine moiety and retains it in the product. The reaction is metal catalyzed and proceeds through a porphyrin Co(III)-nitrene radical intermediate, which is known to form on activation of organic azides at the cobalt center. The synthesized o-aminoazobenzenes are bathochromatically shifted, as compared to azobenzenes without amine substituents. Based on the crystal structure of one of the products, strong H-bonding between the N-atom of the azo functionality and the H of the NH2 substituent is shown to stabilize the trans isomeric form of the product. The NH2 substituents offers possibilities for further functionalization of the synthesized azo compounds. View Full-Text
Keywords: azides; azobenzenes; nitrene radicals; base-metals; dyes; molecular switches azides; azobenzenes; nitrene radicals; base-metals; dyes; molecular switches

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Goswami, M.; de Bruin, B. Porphyrin Co(III)-Nitrene Radical Mediated Pathway for Synthesis of o-Aminoazobenzenes. Molecules 2018, 23, 1052.

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