Molybdate ionic liquids as halide-free catalysts for CO 2 fixation into epoxides

• Published in: Green chemistry : an international journal and green chemistry resource : GC 2023-06, Vol.25 (12), p.4849-4860
• Main Authors: Bragato, Nicola, Perosa, Alvise, Selva, Maurizio, Fiorani, Giulia, Calmanti, Roberto
• Format: Article
• Language: English
• ISSN: 1463-9262; 1463-9270
• DOI: 10.1039/D2GC04475G

Herein we describe the syntheses of a series of molybdate and polyoxomolybdate ionic liquids (ILs), their full spectroscopic characterisation (FT-IR, 1 H-, 13 C-, 31 P-, and 95 Mo-NMR and ICP-MS), a comparison of their properties, and their applications as bifunctional catalysts for CO 2 insertion into epoxides. The synthetic procedures to obtain ILs rely on anion exchange and acid–base reactions, including an innovative route for the synthesis of molybdate ionic liquids (Mo-ILs) using a halide-free organic IL precursor. The use of Mo-ILs as catalysts for CO 2 fixation was investigated using 1,2-epoxyhexane as a model substrate. In the presence of 2.5 mol% of tetrabutylammonium molybdate, hexane carbonate was obtained in up to 86% yield at T = 120 °C, p 0 (CO 2 ) = 30 bar in t = 9 h, under solventless conditions and without any added halide co-catalysts. The substrate scope was broadened to other 12 terminal and internal epoxides; moreover, the reaction was scaled up to 2 g of the substrate and catalyst recyclability was demonstrated up to 5 recycles.