Synthesis of Cyclic Carbonates Catalysed by Aluminium Heteroscorpionate Complexes

Abstract

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 κ(2)-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.

Carbocation/Polyol Systems as Efficient Organic Catalysts for the Preparation of Cyclic Carbonates

“…To investigate the mechanism of the reaction, deuterated epoxides 3 a , b were used to study the stereochemistry of the reaction (Scheme ). In both cases, deuterated cyclic carbonates 4 a , b were formed with predominant retention of the epoxide stereochemistry.…”

“…Notably, the inexpensive diol BINOL was more active than the TADDOL derivatives. The greater acidity of BINOL (pK a =13.2 in DMSO) and its lower steric bulk compared to TADDOL (pK a =19.2 in DMSO) could explain this observation. The use of terephthalic acid with BGI (Table , run 11) resulted in complete inhibition of the activity of BGI.…”

MnIII Porphyrins: Catalytic Coupling of Epoxides with CO2 under Mild Conditions and Mechanistic Considerations

“…Nitrogenated bases did not perform the reaction (entries 34 and 35, Table ), presumably because of the high coordination ability of 1‐methylimidazole and DMAP . Metalloporphyrins MnP1‐6 are five‐coordinated complexes with a square pyramidal geometry (Figure ), so there is a free vacant site at the metallic center where the epoxide should coordinate to suffer the cycloaddition.…”

Self‐Assembly of Luminescent Lanthanide Mesocates as Efficient Catalysts for Transforming Carbon Dioxide into Cyclic Carbonates

“…Thus, we assume that the ytterbium metal in the complex plays the role of a Lewis acid, which was reported for other lanthanide‐based catalysts for the same reaction . Similar to main‐group and transition‐metal Lewis acidic species, the Yb complex first coordinates to the epoxide to form intermediate A . Then, a bromide ion from the TBAB co‐catalyst nucleophilically attacks the coordinated epoxide of intermediate A , which causes opening of the epoxide ring to generate alkoxide species B .…”