【Frontiers in HaiChuan Chemical Technology】Teams from South China University of Technology and Zhejiang Sci-Tech University achieve 1,1-polymerization of acetylene for the first time

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The 1,1-polymerization of acetylene was achieved for the first time. In the history of polymer science, the polymerization of acetylene has held a pivotal role, and it led to the awarding of the Nobel Prize in Chemistry in 2000. However, all known polyacetylenes are obtained through 1,2-addition polymerization of triple bonds. Today, this pattern has been broken. The team led by Zhu Shifa from South China University of Technology/Zhejiang Sci-Tech University took a different approach; by employing an iterative 1,1-carboronation reaction of acetylene and a novel cadmium catalyst, they successfully achieved 1,1-polymerization of acetylene gas for the first time, thereby synthesizing a new class of materials with unique structures and distinct properties – 1,1-polyacetylene – which are explosive in nature. This research not only fills a long-standing gap in the field of alkyne polymerization but also opens up new avenues for polymer materials. Figure 1. Background of 1,1-polyacetylene synthesis. a. Comparison of 1,2-polymerization and 1,1-polymerization: the former has been extensively studied, while the latter has not been reported previously. b. Sherburn et al. synthesized dendrimerene through cross-coupling. c. Dong and Liu synthesized similar structures via the SNV mechanism. d. Zhu and Zheng utilized copper-catalyzed strain accumulation for olefin polymerization. e. Polyhomologation of methylthierythritol. f. The one-step 1,1-carborination reaction reported by Lalic et al. g. The iterative 1,1-carborination polymerization mechanism proposed in this study uses acetylene gas as the monomer, featuring high atom economy and functional group tolerance. Since its discovery in the 1970s, conductive polyacetylene (1,2-polyacetylene) has been a focus of research in materials science. However, its isomer—1,1-polyacetylene obtained via 1,1-addition across the triple bond—cannot be prepared through the direct polymerization of acetylene, and must be synthesized through indirect methods such as multi-step coupling with other synthons. Inspired by the 1,1-carborination reaction of alkynes in boron chemistry, Professor Zhu Shifa’s team designed an iterative acetylene 1,1-carborination process catalyzed by cadmium (Cd) to achieve 1,1-chain polymerization of acetylene using boron atoms as active chain ends. The specific mechanism of this reaction involves the formation of a tetra-coordinated alkynylborane when acetylene reacts with borane; under the catalysis of a Lewis acid, a 1,2-boron to carbon migration occurs in this tetra-coordinated alkynylborane, resulting in the formation of a new alkenylborane. Subsequent demetalation and protonation then lead to the insertion of a single monomer unit. The 1,1-polymerization of acetylene can be achieved as this chain-growth process is iterated. The main challenge in this reaction is how to prevent the newly formed allylboranes from undergoing deboronation and protonation, which would lead to chain termination, as well as how to avoid the occurrence of the thermodynamically more favorable 1,2-addition polymerization of acetylene.