Distance-Selected Topochemical Dehydro-Diels–Alder Reaction of 1,4-Diphenylbutadiyne toward Crystalline Graphitic Nanoribbons

Solid-state topochemical polymerization
(SSTP) is a promising method
to construct functional crystalline polymeric materials, but in contrast
to various reactions that happen in solution, only very limited types
of SSTP reactions are reported. Diels–Alder (DA) and dehydro-DA
(DDA) reactions are textbook reactions for preparing six-membered
rings in solution but are scarcely seen in solid-state synthesis.
Here, using multiple cutting-edge techniques, we demonstrate that
the solid 1,4-diphenylbutadiyne (DPB) undergoes a DDA reaction under
10–20 GPa with the phenyl as the dienophile. The crystal structure
at the critical pressure shows that this reaction is “distance-selected”.
The distance of 3.2 Å between the phenyl and the phenylethynyl
facilitates the DDA reaction, while the distances for other DDA and
1,4-addition reactions are too large to allow the bonding. The obtained
products are crystalline armchair graphitic nanoribbons, and hence
our studies open a new route to construct the crystalline carbon materials
with atomic-scale control.

固态拓扑化学聚合（Solid-state topochemical polymerization, SSTP）是构建功能性结晶高分子材料的极具潜力的方法，但与溶液中发生的各类反应相比，目前报道的SSTP反应类型极为有限。狄尔斯-阿尔德（Diels–Alder, DA）反应与脱氢狄尔斯-阿尔德（dehydro-DA, DDA）反应是溶液中制备六元环的教科书中的经典反应，但在固态合成中却鲜有报道。本研究借助多项前沿技术，证实固态1,4-二苯基丁二炔（1,4-diphenylbutadiyne, DPB）在10~20 GPa压强下，以苯基作为亲双烯体发生DDA反应。临界压强下的晶体结构表明，该反应具有"距离选择性"：苯基与苯乙炔基之间3.2 Å的距离促进了DDA反应的发生，而其他DDA反应与1,4-加成反应所需的距离均过大，无法成键。所得产物为结晶性扶手椅型石墨纳米带，因此本研究为实现原子级精准调控的结晶碳材料构建开辟了全新路径。