Estudi de la reactivitat d’un complex organometàl·lic de Co(III) amb azides

Abstract

More versatile and selective synthetic methodologies are highly desired and are one of the main reasons of chemistry research. In this context, Pd-catalyzed cross-coupling reactions have become a powerful and appreciated strategies for the functionalization of different molecules. However, direct C-H functionalization reactions could become an even more efficient and cleaner option. Unfortunately, these methodologies are mostly based on the second and third transition metals. Although, they are completely functional, these metals are very environmentally dangerous and their low abundance makes them very expensive. Therefore, the development of new methodologies based on first row transition metals such as Fe, Co, Ni and Cu is needed. Among them, Co(III) had been unknown until six years ago, and its chemistry still remains quite non-understood. Even though, it has demonstrated its capability to act as Rh substitute in many reactions. Several contributions have been done with this metal by QBIS-CAT research group. Following their work, the preparation of two different Co(III) organometallic complex have been addressed via C-H activation, aiming to functionalize the C-Co(III) bond using several organic and inorganic azides to achieve the new C-N bond, via Co(III)-nitrene intermediates formation. The first section of this work is based on the synthesis of the macrocyclic ligand and the Co(III) complex previously reported. Secondly, we have explored its reactivity in front of three different organic azides. Only the product derived from the benzyl azide has been isolated and characterized. Several attempts have been performed on the formation of the corresponding product using (2-azidoethyl)benzene (Az2) and (3-azidopropil)benzene (Az3), however no product formation was achieved. The relative position of the benzyl group to the new aryl-N has been identified as a critical factor on these reactions, showing reactivity for the Az2 and Az3. This factor has allowed us to identify a possible Co(IV) complex, which could be an intermediate in these kind of reactions. Finally, the functionalization of Co(III)-C bond to form a new C-N bond using a sodium azide as inorganic azide was also investigated. Several conditions and strategies have been performed, however in all the cases only the coordination of N3 moiety on the Co(III) complex was observed