Polymer-bound aluminium salen complex as reusable catalysts for CO2 insertion into epoxides

Two polymeric aluminium salen complexes in where the backbones are either a partially crosslinked polystyrene [(Al(salen)/PS)] or poly(ethylene glycol bismethacrylate) [(Al(salen)/PEA)] have been synthesised and used for the carbon dioxide insertion into epoxides to form cyclic carbonates. The catalytic activity of these polymers is similar to that of the unsupported aluminium salen complexes, and the polymeric catalysts can be easily separated from the reaction mixture and reusable in consecutives runs. The activity and reusability of the polymeric salen complex depends on the nature of the polymer: PEA being a polymer with a high oxygen content in the backbone enhances the initial activity as compared to PS, but Al(salen)/PEA exhibits lower stability as compared to Al(salen)/PS and a Al depletion occurs upon use. The presence of nucleophiles such as N-methylimidazole or N,N-dimethylaminopyridine in excess increases the catalytic activity of the polymeric Al(salen) catalyst. Also polymeric nucleophiles have been found to be suitable reusable co-catalysts for this reaction.