Catalisi del rame in reazioni di reazioni di ossidazione e riduzione: C-H amminazioni ossidative di benzossazolo mediate dal Cu(I) e utilizzo di nanoparticelle di Cu per N-alchilazione riduttiva del nitrobenzene.

Affordability, versatility, low toxicity and abundance are the main factors that make copper-based catalysts so desirable for organic chemistry. The versatility of copper is mainly due to its ability to transfer one or two electrons. For this reason, organic transformations such as oxidation and reduction, gain particular advantage by the use of copper catalysis. In the present work two research projects have been carried out to explore the abilities of copper in redox transformations: first, a cross-dehydrogenative coupling protocol between benzoxazole and a range of secondary amines using Cu(I) was optimised ant the products characterized; secondly, the potential of copper nanoparticles to catalyse the synthesis of N-substituted anilines starting from nitrobenzene and alcohols in a tandem reaction was studied. Cross dehydrogenative coupling reactions are a tool of great importance in synthetic organic chemistry, allowing the direct functionalization of C-H bonds with the aid of a stoichiometric oxidant to achieve C-C and C-heteroatom bonding. Several procedures exist for the copper-catalysed direct amination of azoles: major drawbacks include the use of oxygen, the need to use a large excess of amine, low azole substrate versatility and, lastly, acidic or basic conditions.1 The aim of the present work was to optimise a ligandless, acid- and base-free procedure in ambient air and demonstrate its applicability to a wide range of amines. Moderate results were obtained using CuCl as catalyst, relatively mild heating (82°C) and, most importantly, without the need of ligand or acid/base additives. This straightforward procedure is proposed as a complementary tool with respect to existing literature in the direct amination of azoles, notably when neutral conditions are needed. Simultaneously, the ability of metallic copper nanoparticles (Cu NPs), both alone and supported on inorganic matrices, to catalyse a novel synthetic route to N-substituted anilines from nitrobenzene was studied. A hydrogen borrowing process was investigated with the aim to obtain secondary amine from nitrobenzene in presence of benzyl alcohol as source of hydrogen. The intermediate production of benzaldehyde could react with aniline to form the N-alkylated product through a hydrogen borrowing mechanism with the help of copper. While such reactivity has been previously reported using expensive noble metals (Ru, Pd and Au), a copper catalysed procedure has never been reported. Different conditions have been tested using benzyl alcohol as both reactant and solvent: results show that use of a strong base and high temperatures (130°C) are needed, and that Cu NPs supported on alumina is the best catalytic system between the ones investigated. Use of a supplementary hydrogen source (glycerol) and use of microwaves have also been investigated to increase efficiency and to reduce reaction time. Although the secondary amine product was never detected, during this preliminary study the intermediate imine was obtained as the major product.