Chiral diboranes as catalysts for the stereoselective organopolymerization of epoxides

Abstract

It is demonstrated that stereoselective polymerization of epoxides, long a domain of metal-based compounds, can also be achieved via the application of organocatalysts. A simple two-step synthesis starting from widely available 1,1′-bi-2-naphthol (BINOL) backbones yields diboranes which, in tandem with organobases, deliver isotactic-enriched (it) polyethers from the homopolymerization of racemic propylene oxide (PO) and other epoxides. Thereby, isotactic diad contents of up to 88% can be achieved, resulting in well-defined (1.1 < ĐM < 1.3) polyethers with high molar masses (Mn > 100 000 g mol−1). Notably, it is also possible to grow it-enriched sequences of PPO on aliphatic polyester-type initiators, thus enabling the incorporation of stereocontrolled polyether blocks in more complex polymer architectures. It is expected that this ability will greatly benefit the preparation of polyether-containing additives. The BINOL-type diboranes can be readily modified, suggesting further potential as a platform from which optimized catalysts can be developed.