Although bacterial stereoregular polyhydroxyalkanoates have attracted broad interest as sustainable materials, it remains a long-standing challenge to chemically synthesize stereoregular polyhydroxyalkanoates via the stereoselective ring-opening polymerization of four-membered lactones. Here we report the design and synthesis of a class of readily tunable spiro-salen yttrium complexes for stereoselective ring-opening polymerization of rac-β-butyrolactone. Ligand modification on this spiro-salen system allowed a switch from syndioselectivity to isoselectivity, producing syndiotactic poly(3-hydroxybutyrate) (probability of racemic linkages between monomer units up to 0.99) and isotactic poly(3-hydroxybutyrate) (probability of meso linkages between monomer units up to 0.95). A complete stereoselectivity switch between enantiopure and racemic catalysts was observed for the spiro-binaphthol-salen system. Incorporation of rac-β-valerolactone into poly(3-hydroxybutyrate) afforded stereoregular poly(3-hydroxybutyrate-co-3-hydroxyvalerate)s with high molecular weight and desirable material properties comparable to commercial material polyolefins. This spiro-salen ligand system provides a conceptual framework that could guide future stereoselective catalyst design efforts.

尽管细菌有规立构聚羟基脂肪酸酯作为可持续材料引起了广泛的兴趣，但通过四元内酯的立体选择性开环聚合化学合成有规立构聚羟基脂肪酸酯仍然是一个长期存在的挑战。在这里，我们报道了一类易于调节的螺-salen钇配合物的设计和合成，用于外消旋-β-丁内酯的立体选择性开环聚合。这种螺-salen系统的配体修饰允许从间选择性转变为等选择性，产生间规聚（3-羟基丁酸酯）（单体单元之间外消旋键的概率高达0.99）和全同立构聚（3-羟基丁酸酯）（内消旋键的概率）单体单元之间的连接高达 0.95）。对于螺环-联萘酚-salen 系统，观察到对映体纯和外消旋催化剂之间的完全立体选择性转换。将外消旋-β-戊内酯掺入聚(3-羟基丁酸酯)中可得到有规立构的聚(3-羟基丁酸酯-共-3-羟基戊酸酯)，其具有高分子量和与商业材料聚烯烃相当的理想材料性能。这种螺-salen配体系统提供了一个概念框架，可以指导未来的立体选择性催化剂设计工作。