Yttrium Phosphasalen Initiators for <i>rac</i>-Lactide Polymerization: Excellent Rates and High Iso-Selectivities

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 (Pi = 0.84) or hetero-selectivities (Ps = 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.本研究报道了用于外消旋丙交酯（rac-lactide）立体可控开环聚合的高活性钇基膦沙伦（phosphasalen）引发剂。该类引发剂由一类新型辅助配体配位得到：即经典沙伦（salen）配体的亚胺基膦烷衍生物，被命名为“膦沙伦（phosphasalen）”。通过调控膦沙伦配体的分子结构，可实现高值等规选择性（Pi=0.84）或间规选择性（Ps=0.87）。该类引发剂同时具备极高的聚合速率、优异的聚合可控性，且可耐受极低的催化剂负载量；此外，其立体调控过程无需引入手性助剂或手性配体。兼具高聚合速率与高等规选择性的特性极为罕见。