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

Abstract

Utilising the oxygen‐vacancy‐mediated reactivity of CaO/CuO and hydrazine monohydrate in isopropyl alcohol at 353 K, a variety of amino‐derivatives of N‐heterocycles, including pyridine, indole, quinoline, isoquinoline, and benzothiazole, have been selectively synthesised by reducing their nitro analogues. It is demonstrated that CaO/CuO composite is a reusable, solvent‐resilient solid reducing agent that can reduce a variety of nitro‐N‐heterocyclic substrates. The critical role of the structure of CaO/CuO on the nitro‐reduction activity has been studied using spectroscopy and microscopy. DFT simulations indicate the facile formation of oxygen vacancies (EO,vac =‐ 43.4 kJ/mol) on the interface of CaO/CuO surface under reducing environment. The presence of CaO facilitated a stronger interaction of the nitro‐substrate on the oxygen vacant CuO (111) surface, resulting into a significantly lower activation energy (Ea = 21.9 kJ/mol) for N‐O dissociation. The reaction could be scaled up from 1 to 12 mmol of substrate. CaO/CuO is a reusable and a cost‐effective alternative to the conventional catalyst (Pd/C, Pt/C).

Harnessing the Oxygen Vacancies in Metal Oxides for Nitroreduction

“…Eventually, modified CuO showed better reactivity and stability. [39][40][41][42][43] Although metal is an important constituent in these oxides, the CuO may stand apart from the classical metal-acid or metal-H 2 -based catalysts (Scheme 1) by the nature of the reactivity of the active sites. The V o -mediated reactive solids present a new scope as a non-noble metal-based reaction system for the synthesis of amines.…”