AbstractsChemistry

The insertion of a nitrene “RN” functionality into a C-H bond represents a valuable tool achieving a wide variety of nitrogen-containing fine chemicals, which frequently present pharmaceutical and/or biological properties. The key point to perform sustainable amination reactions are: i) The selection of a selective, active and stable catalytic system ii) The use of nitrene sources presenting high reactivity and atom efficiency. The last characteristic is well exhibited by organic azides (RN3)1 which transfer a nitrene functionality to an organic skeleton by yielding eco-friendly N2 as the only stoichiometric by-product. The reaction of RN3 with organic compounds can be thermally or photochemically promoted2 but, to improve the reaction selectivity, the presence of a metal catalyst is required. Amongst the catalysts used to achieve these chemical transformations,3, 4 metal porphyrins show a good catalytic efficiency coupled with a very high chemical stability.5 In the last decade, in our research group, we have studied the efficiency of cobalt6, 7 and ruthenium8 porphyrin complexes in catalysing the amination of a wide class of substrates by using ayl azides as nitrene sources. In this research project we have in-depth investigated the behavior of these catalysts in allylic9, inter10- and intra11 benzilic aminations. First, we have explored the catalytic activity of Ru(TPP)CO (TPP = dianion of tetraphenylporphyrin) in intermolecular benzylic amination reactions10, several benzylic substrates were reacted with different aryl azides employing the hydrocarbon as the reaction solvent and the catalytic ratio Ru(TPP)CO/azide = 4:50. It was observed that Ru(TPP)CO was also active in the amination of benzylic substrates containing an endocyclic benzylic C-H bond. The corresponding amines have been isolated in good yields. To investigate the mechanism of the benzylic amination catalyzed by Ru(TPP)CO, a kinetic study was undertaken. The analysis of kinetics and reaction selectivities indicated the formation of an active ruthenium (VI) imido complex as a catalytic intermediate. More in-depth studies will be necessary to better clarify the reaction mechanism of the amination of benzylic C-H bonds. Since Ru(TPP)CO has demonstrated to be a good catalyst in benzylic amination reactions we have subsequently studied the activity of this catalyst in allylic amination reactions9. Believing that an important step for the improvement of the catalytic efficiency of the reported methodology is the comprehension of the reaction mechanism, we first studied the catalyst reactivity towards the components of a model reaction, cyclohexene and azide. No catalyst modification was observed by 1H NMR when Ru(TPP)CO was suspended in cyclohexene and refluxed for a couple of hours, on the other hand, the reaction between Ru(TPP)CO and an 3,5(CF3)2C6H3N3 excess yielded the bis imido complex Ru(TPP)(NAr)2 which showed a catalytic activity similar or even better than that described for Ru(TPP)CO, his precursor. To assess if the formation of a bis-imido…