Enantiopure SPINOL Based Dinuclear Borane for the Stereoselective Polymerization of Propylene Oxide

Stereoselective polymerization of epoxides has traditionally relied on metal-based catalysts, yet the presence of residual metals restricts their use in sensitive applications such as biomedicine. Chiral borane catalysis offers a promising metal-free alternative, though most reported systems display limited structural diversity and modest stereocontrol. Herein, we report the design and synthesis of enantiopure SPINOL-derived dinuclear borane catalysts that enable highly efficient and stereoselective polymerization of racemic propylene oxide (PO). Under optimized conditions (–20 °C in THF), the catalysts produced isotactic poly(propylene oxide) (PPO) with a meso dyad content ([m]) of 93%. Kinetic studies reveal a distinct enantiomeric matching between catalyst configuration and PO enantiomers, in sharp contrast to the mismatched preference observed with BINOL-based analogues. The polymerization proceeded via an enantiomorphic site-control mechanism, with a maximum selectivity factor (s) of 34.8. These results highlight the potential of SPINOL frameworks as versatile chiral platforms for advancing the development of high-performance borane catalysts in stereoselective polymerization.