Lewis Pair of Triethylborane and DBU Usable for the Metal-free Copolymerization

A Lewis pair (1) formed from a Lewis acid such as triethylborane and a Lewis base such as 1,8-Diazabicyclo[5.4.0]-7-undecene(DBU) can be used as a metal-free copolymerization catalyst. For instance, a 1-catalyzed regioselective copolymerization of propylene oxide(PO) with carbonyl sulfide(COS) proceeds to give the related polymers with high transparence and high polymerization degree. In this copolymerization, 1 promotes by binding to PO followed by the insertion of COS thereby activating PO, and resultantly gives high tail-to-head content polymers. In this way, 1 is useful for metal-free copolymerizations. Further development of this approach should attract attention.