Issue 3, 2022

Synthesis and characterisation of an enantiomerically pure scandium pentadienyl complex and its application in the polymerisation of rac-lactide

Abstract

The alkyl-functionalised scandium complex [(pdl*SiMe2NtBu)Sc(thf)(CH2SiMe3)] (2) was synthesised in enantiomerically pure form and characterised by NMR spectroscopy and X-ray diffraction analysis. Complex 2 features a chiral constrained geometry ligand derived from the natural compound (1R)-(−)-myrtenal, in which the pentadienyl (pdl*) fragment coordinates in η32-allyl-en fashion to the scandium atom. Compound 2 catalyses the polymerisation of rac-lactide at 30 °C and 50 °C yielding amorphous poly(lactide) with slightly heterotactic enchainment (Pm = 0.36 and 0.37). In agreement with the data obtained from GPC and DSC measurements, a chain-end control mechanism is proposed with fast chain propagation relative to the initiation, which leads to broad molecular weight distributions (Đ ≈ 1.80) and higher than expected molecular weights. Furthermore, chain transfer processes are observed, but only small amounts of transesterification and racemisation occur. Kinetic studies reveal a second-order dependence in rac-lactide (monomer) concentration and a first-order dependence in the concentration of catalyst 2.

Graphical abstract: Synthesis and characterisation of an enantiomerically pure scandium pentadienyl complex and its application in the polymerisation of rac-lactide

Supplementary files

Article information

Article type
Paper
Submitted
19 Nov 2021
Accepted
14 Dec 2021
First published
21 Dec 2021

Dalton Trans., 2022,51, 986-997

Synthesis and characterisation of an enantiomerically pure scandium pentadienyl complex and its application in the polymerisation of rac-lactide

K. Münster, J. Raeder and M. D. Walter, Dalton Trans., 2022, 51, 986 DOI: 10.1039/D1DT03920B

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