Synthesis of Cyclic Carbonates Catalysed by Aluminium Heteroscorpionate Complexes

• Published in: Chemistry : a European journal 2015-06, Vol.21 (27), p.9850-9862
• Main Authors: Martínez, Javier, Castro-Osma, José A., Earlam, Amy, Alonso-Moreno, Carlos, Otero, Antonio, Lara-Sánchez, Agustín, North, Michael, Rodríguez-Diéguez, Antonio
• Format: Article
• Language: English
• Subjects: aluminium complexes; Aluminum; Bimetals; Carbon dioxide; Carbonates; Catalysis; Catalysts; Chemistry; cyclic carbonates; epoxides; Synthesis; Tetrabutylammonium bromide
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201500790

New aluminium scorpionate based complexes have been prepared and used for the synthesis of cyclic carbonates from epoxides and carbon dioxide. Bimetallic aluminium(heteroscorpionate) complexes 9–14 were synthesised in very high yields. The single‐crystal X‐ray structures of 12 and 13 confirm an asymmetric κ2‐NO‐μ‐O arrangement in a dinuclear molecular disposition. These bimetallic aluminium complexes were investigated as catalysts for the synthesis of cyclic carbonates from epoxides and carbon dioxide in the presence of ammonium salts. Under the optimal reaction conditions, complex 9 in combination with tetrabutylammonium bromide acts as a very efficient catalyst system for the conversion of both monosubstituted and internal epoxides into the corresponding cyclic carbonates showing broad substrate scope. Complex 9 and tetrabutylammonium bromide is the second most efficient aluminium‐based catalyst system for the reaction of internal epoxides with carbon dioxide. A kinetic study has been carried out and showed that the reactions were first order in complex 9 and tetrabutylammonium bromide concentrations. Based on the kinetic study, a catalytic cycle is proposed. Mild conditions: A combination of a bimetallic aluminium(scorpionate) complex and tetrabutylammonium bromide catalyses the formation of cyclic carbonates from terminal and internal epoxides and carbon dioxide under mild reaction conditions.