Conformationally Locked Yttrium Indanosalan Complexes for Fast Isoselective Ring-Opening Polymerization of β-Butyrolactone at Elevated Temperatures

We report rigid yttrium indanosalan complexes for the high-temperature ring-opening polymerization of β-butyrolactone. Some of the complexes (isolated or obtained in situ) developed were able to polymerize β-butyrolactone with high isoselectivity (Pm = 0.88) and very high activity (TOF up to 135,000 h–1) at a polymerization temperature of 100 °C, at which the polymer remains in solution, facilitating its further processing. Polymerization at 30–60 °C yielded the poly(3-hydroxybutyrate)s with Pm up to 0.94. The roles of active site configuration and non-covalent interactions were studied experimentally and by DFT, which reproduced the enantiomorphic-site control and showed that the monomer was oriented by C–H···π and C–H···O contacts, rather than by N–H···O hydrogen bonding.