Yttrium phosphasalen initiators for rac-lactide polymerization: excellent rates and high iso-selectivities.

Clare Bakewell, Thi-Phuong-Anh Cao, Nicholas Long, Xavier F Le Goff, Audrey Auffrant, Charlotte K Williams

Index: J. Am. Chem. Soc. 134(51) , 20577-80, (2012)

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Abstract

Highly active yttrium phosphasalen initiators for the stereocontrolled ring-opening polymerization of rac-lactide are reported. The initiators are coordinated by a new class of ancillary ligand: an iminophosphorane derivative of the popular "salen" ligand, termed "phosphasalen". Changing the phosphasalen structure enables access to high iso-selectivities (P(i) = 0.84) or hetero-selectivities (P(s) = 0.87). The initiators also show very high rates, excellent polymerization control, and tolerance to low loadings; furthermore, no chiral auxiliaries/ligands are needed for the stereocontrol. The combination of such high rates with high iso-selectivities is very unusual.