The synthesis, characterisation and application of iron(iii)–acetate complexes for cyclic carbonate formation and the polymerisation of lactide

Abstract

Herein, we report the preparation, characterisation and catalytic applications of air-stable Fe(III)–acetate complexes consisting of salan, salen and salalen ligand frameworks. Owing to the simple synthetic protocol employed, a wide range of complexes have been prepared and structure–activity-relationships investigated. X-ray diffraction confirmed the solid-state structures for eight of the complexes. These represent the first Fe(III)–acetate complexes applied for the selective coupling of CO₂/epoxide and lactide polymerisation. The coupling of CO₂ and challenging cyclohexene oxide substrate was performed under mild, solvent-free conditions (80 °C, 10 bar CO₂) to selectively form the cis-cyclohexene carbonate as the exclusive product (selectivity >99%) with a metal loading of 0.08 mol%. A reduced aminopiperidine ligand backbone was found as the most active catalyst, and after investigating four co-catalysts, showed high functional group tolerance and robustness when applied to a broad, commercially available, terminal epoxide substrate scope with high conversions observed. The ring-opening polymerisation of rac-lactide was achieved using the Fe(III)OAc complexes using triethylamine and benzyl alcohol for initiation, interestingly isoselectivity was observed in some cases.