A Cu8Na2-silsesquioxane/acetylacetonate precatalyst for the one-pot cyclohexane to ε-caprolactone transformation

Abstract

Self-assembly of heterometallic (copper/sodium) complexes stabilized by phenylsiloxanolate and acetylacetonate ligands resulted in Cu₈Na₂-cage structures. Their unprecedented cage-like geometry features two peripheral Cu₃ and one central Na–Cu₂–Na linear fragments surrounded by two Si₅–cyclic silsesquioxanes and four acetylacetonate ligands. To evaluate its catalytic performance, the Cu₈Na₂-precatalyst was explored in the oxidation of cyclohexane, selected as a model substrate, under a range of experimental conditions. The best results were obtained at 80 °C for 0.5 h under MW irradiation, affording ε-caprolactone (TON = 145, TOF = 290 h⁻¹) along with cyclohexanol and cyclohexanone, in an overall yield of 15%. These promising preliminary findings highlight the potential of the heterometallic Cu₈Na₂ system as an efficient and selective precatalyst for rapid MW-assisted single-pot oxidation, under mild conditions, of cyclohexane to ε-caprolactone, a compound with a marked industrial interest.