Polymerization of ϵ‐Caprolactam to Nylon‐6 Catalyzed by Barium σ‐Borane Complex under Mild Condition

A mild and low‐temperature synthesis of nylon‐6 is achieved through the ring‐opening polymerization of ϵ‐caprolactam using barium σ‐borane complex as the catalyst. Due to the mild nature of the catalyst, this protocol provides an easy means of synthesizing nylon‐6, for the first time with a precise and predictable molecular weight. From various model experiments, it is evident that the σ‐coordinated boron hydride acts as a mild hydride donor in the first step of the reaction to generate lactamate anions, which then undergo ring‐opening polymerization in‐situ with the remaining caprolactam molecules under the influence of the dehydrogenated boron metal complex.