Pressure‐Induced Polymerization of Acetylene: Structure‐Directed Stereoselectivity and a Possible Route to Graphane

• Published in: Angewandte Chemie (International ed.) Vol. 56; no. 23; pp. 6553 - 6557
• Main Authors: Sun, Jiangman, Dong, Xiao, Wang, Yajie, Li, Kuo, Zheng, Haiyan, Wang, Lijuan, Cody, George D., Tulk, Christopher A., Molaison, Jamie J., Lin, Xiaohuan, Meng, Yufei, Jin, Changqing, Mao, Ho‐kwang
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.06.2017; Wiley
• Edition: International ed. in English
• Subjects: Acetylene; Crystallography; Diffraction; Distribution functions; External pressure; graphane; High pressure; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Low temperature; MATERIALS SCIENCE; Neutron diffraction; Neutrons; NMR; Nuclear magnetic resonance; Polyacetylene; Polymerization; Polymers; Pressure; pressure-induced polymerization; Simulation; solid-state reactions; Stereoselectivity; Temperature effects; Textbooks; neutron diffraction; graphane; solid-state reactions; acetylene; pressure-induced polymerization
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201702685

Geometric isomerism in polyacetylene is a basic concept in chemistry textbooks. Polymerization to cis‐isomer is kinetically preferred at low temperature, not only in the classic catalytic reaction in solution but also, unexpectedly, in the crystalline phase when it is driven by external pressure without a catalyst. Until now, no perfect reaction route has been proposed for this pressure‐induced polymerization. Using in situ neutron diffraction and meta‐dynamic simulation, we discovered that under high pressure, acetylene molecules react along a specific crystallographic direction that is perpendicular to those previously proposed. Following this route produces a pure cis‐isomer and more surprisingly, predicts that graphane is the final product. Experimentally, polycyclic polymers with a layered structure were identified in the recovered product by solid‐state nuclear magnetic resonance and neutron pair distribution functions, which indicates the possibility of synthesizing graphane under high pressure. From acetylene to graphane: By using neutron diffraction and theoretical calculations the domination of cis‐polyacetylene in the pressure‐induced polymerization of C2H2 is explained. Graphane is predicted as the final product and a layered polycyclic polymer was identified experimentally as an intermediate between polyacetylene and graphane.