Iron(III) Salalen Complexes for the Polymerisation of Lactide

Abstract

Herein, we report the preparation and characterisation of iron(III) salalen complexes, with variation of ligand substituents and backbone investigated. Six new complexes were prepared and characterised by elemental analysis, mass spectrometry and X-ray crystallography. These complexes have been applied for the ring opening polymerisation (ROP) of rac-lactide

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

“…2). As was observed for the Fe(X)Cl complexes, 10 . Fe(6 meso )OAc, with a restricted bipyrrolidine salan backbone and methyl substituents on the aromatic rings, gave a small preference for the tbp geometry (τ = 0.58), however, increasing the steric bulk of these substituents to t Bu groups forced the preference to increase moderately {Fe(7 meso ) OAc, τ = 0.63}.…”

“…This geometry is analogous to the Fe(III)-chloride complexes previously reported. 10 This is evident when comparing Fe(2)OAc and the analogous iron-chloride salalen complex {Fe(2)Cl}. Overlaying the solid-state structures shows the chloride and the central carbon of the acetate occupying the same equatorial position ( Fig.…”

“…The degree of transesterification is negligible. Compared to the chloride analogues, 10 Fe(1-2)OAc were less active, requiring higher temperatures to achieve moderate conversion. The iron salan acetate complexes typically achieved higher conversion relative to the salalen complexes.…”

“…We recently reported a variety of Fe(III)-salalen complexes that followed this mechanism. 10 Moderate isotacticity (P m = 0.75-0.80) and good molecular weight control in PO were observed (Đ = 1.02-1.18). Batch kinetics using an Fe(III)-salalen complex indicated there was an induction period within the six hours, likely relating to the in situ generation of the Fe(III)alkoxide species.…”

“…A resurgence of iron catalysed reactions has been seen in the ring-opening polymerisation (ROP) of cyclic esters, such as lactide, and the catalytic transformation of CO 2 , such as with the coupling of epoxides. [5][6][7][8][9][10][11][12] Poly(lactic acid) (PLA) is a more sustainable, renewable, biodegradable and biocompatible alternative plastic compared to those derived from crude oil, with the potential for a 'closedloop' lifecycle. 13,14 PLA can be used in food packaging, drug delivery systems and biomedical applications.…”