Azobenzene synthesis from non-aromatic compounds enabled by alloy-controlled dehydrogenation catalysis

Azobenzenes have been ubiquitously utilised and synthesised in well-established methods represented as azo coupling since long; however, all the available azobenzene synthesis strategies use aromatic compounds as substrates, which inherently limit the regioselectivity of substituents because of ortho/meta/para-orientation and frequently require multi-step procedures. Dehydrogenative aromatisation from cyclohexanones, which can be regioselectively functionalised using classical methods without the aforementioned limitation, has recently attracted much attention, but the lack of multi-functional dehydrogenation catalysts for both aromatisation and azo bond formation and/or the difficult product selectivity control have hindered its application in azobenzene synthesis. Herein, we report an unprecedented strategy for the synthesis of diverse azobenzenes, including unsymmetrical ones, from non-aromatic compounds, i.e. cyclohexanones and hydrazine, using an Au–Pd alloy nanoparticle catalyst and nitrobenzene. Thorough mechanistic studies revealed that the present reaction is enabled by adsorption control and relay catalysis involving concerted dehydrogenation, which are unique features to alloy nanoparticles.