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Wiley, Angewandte Chemie, 35(126), p. 9380-9384, 2014

DOI: 10.1002/ange.201403643

Wiley, Angewandte Chemie International Edition, 35(53), p. 9226-9230, 2014

DOI: 10.1002/anie.201403643

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Metal-Size Influence in Iso-Selective Lactide Polymerization**

Journal article published in 2014 by Clare Bakewell, Andrew J. P. White, Nicholas J. Long, Charlotte K. Williams ORCID
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Abstract

Iso-selective initiators for the ring-opening polymerization (ROP) of rac-lactide are rare outside of Group 13. We describe the first examples of highly iso-selective lutetium initiators. The phosphasalen lutetium ethoxide complex shows excellent iso-selectivity, with a Pi value of 0.81-0.84 at 298 K, excellent rates, and high degrees of polymerization control. Conversely, the corresponding La derivative exhibits moderate heteroselectivity (Ps =0.74, 298 K). Thus, the choice of metal center is shown to be crucial in determining the level and mode of stereocontrol. The relative order of rates for the series of complexes is inversely related to metallic covalent radius: that is, La>Y>Lu.