Oxygen Vacancy-Mediated Reactivity: The Curious Case of Reduction of Nitroquinoline to Aminoquinoline by CuO

Abstract

Reduction of nitroarenes is a useful strategy for the preparation of aromatic amines. In this work, CuO was used as a reusable solid reagent for the reduction of nitroquinolines to aminoquinolines using hydrazine monohydrate as the hydrogen donor under mild reaction conditions. The reaction of 0.5 mmol of 5-nitroquinoline to 5aminoquinoline was completed in 10 min with 100% conversion and selectivity. The reagent CuO could be easily collected and reused for up to four cycles, after which it is completely transformed into Cu 2 O and Cu. The high activity and selectivity of CuO were attributed to the facile formation of oxygen vacancies on the CuO surface under the reducing environment, as confirmed by X-ray photoelectron spectroscopy. Further, density functional theory simulations showed that oxygen vacancies led to higher adsorption (E ads = −174.4 kJ/mol) and selective activation of the nitro group (E a = 43 kJ/mol) coupled with a reaction involving hydrogen atoms activated on the CuO surface. However, the presence of an additional pyridine ring in 5-nitroquinolines slightly impeded the rate of complete reduction (t = 10 min).

Oxygen Vacancy Mediated Reactivity of CaO/CuO Composite for the Synthesis of Amino‐N‐heterocycles

“…This trend in the reduction of activation barrier in presence of Ov is consistent with our previous study on 5-NQ reduction over CuO (111) (E a = 60 kJ/mol) and CuOv (111) surface (E a = 43 kJ/mol). [58] Further the NÀ O2 bond dissociation step was found to be exothermic on both the stoichiometric CaO/CuO surface (E rxn = À 3.9 kJ/mol, Figure 5 1a to 1b) and non-stoichiometric CaO/CuO surface (E rxn = À 43.4 kJ/mol, Figure 5a to b) respectively. Thus, the presence of CaO on CuO (111) surface reduces the NÀ O dissociation barrier for 5-NQ compared to both stoichiometric and non-stoichiometric CuO (111) surfaces (E a = 60 and 43 kJ/mol) [19] which is in line with the experimental observation where CaO/CuO exhibited 100 % conversion in comparison to bulk CuO which gave only 59 % conversion of 5-NQ.…”

Cationic and oxygen defect modulation for tailoring the bandgap and room temperature ferromagnetism of CuO via multiple d-block cations

“…In general, a significant amount of oxygen vacancies, along with other point defects, are common on the surface of nanoscale semiconductors like CuO because of the size effects. 18 The point defects strongly affect the energy states, which can modify the optical and magnetic characteristics. Therefore, point defects like lattice oxygen as well as cation vacancies, interstitials, and free charge carriers act as controlling factors for tailoring the bandgap and transport properties of dilute magnetic semiconductors (DMSs) like CuO.…”