Abstract
Two new one-component aluminium-based catalysts for the reaction between epoxides and carbon dioxide have been prepared. The catalysts are composed of aluminium–salen chloride complexes with trialkylammonium groups directly attached to the aromatic rings of the salen ligand. With terminal epoxides, the catalysts induced the formation of cyclic carbonates under mild reaction conditions (25–35 °C; 1–10 bar carbon dioxide pressure). However, with cyclohexene oxide under the same reaction conditions, the same catalysts induced the formation of polycarbonate. The catalysts could be recovered from the reaction mixture and reused.
Highlights
Carbon dioxide is a renewable and inexpensive carbon source, so great efforts have been directed at developing novel methods for the valorization of this abundant raw material [1]
The preparation of salen ligands 8a and 8b was conducted according to Scheme 2, starting from tert-butylphenol, which was formylated and nitrated to produce 5-nitro-3-(tertbutyl)salicylaldehyde (5) [24,25,26,27]. 5-N,N-Dimethylamino-3(tert-butyl)salicylaldehyde (6) was prepared directly from 5, using a literature procedure [28,29]
Ligand 7 was efficiently alkylated under mild reaction conditions using either methyl iodide or benzyl bromide, giving the corresponding positively charged salen ligands 8a and 8b in 95 and 78% yields respectively
Summary
Carbon dioxide is a renewable and inexpensive carbon source, so great efforts have been directed at developing novel methods for the valorization of this abundant raw material [1]. Styrene oxide was used as a model substrate to test the catalytic efficiency of complexes 1 and 2 in the coupling reaction with carbon dioxide. It is apparent from the data that both catalysts are effective at promoting the coupling reaction even at room temperature and bar of carbon dioxide pressure
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