Chiral diboranes as catalysts for the stereoselective organopolymerization of epoxides.

It is demonstrated that stereoselective polymerization of epoxides, long a domain of metal-based compounds, can also be achieved 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 () 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.

A simplified approach for the metal-free polymerization of propylene oxide.

Triethyl borane (EtB), in combination with phosphazene-type superbases, has recently emerged as a powerful co-catalyst for the anionic polymerization of epoxides. Here, it is demonstrated that the monomer-activating property of EtB can also compensate for the application of much gentler organobases. This not only results in simpler setups, but also significantly reduces nucleophilicity/basicity-derived side reactions.