Mechanistical Study on Substrate‐Controlled Highly Selective [2+2] and [2+3] Cycloaddition Reactions

Abstract

Polycyclic conjugated hydrocarbons have acquired increased interests recently because of their potential applications in electronic devices. On metal surfaces, the selective synthesis of four‐ and five‐membered carbon rings remains challenging due to the presence of diverse reaction pathways. Here, utilizing the same precursor molecule, we successfully achieved substrate‐controlled highly selective cycloaddition reactions towards four‐ and five‐membered carbon rings. A 97% yield for four‐membered carbon rings on Au(111), while a 96% yield towards five‐membered carbon rings is achieved on Ag(111). The detailed topological structures of the reaction products are carefully examined by bond‐resolving scanning tunneling microscopy (BR‐STM) imaging with a CO functionalized tip. The underlying mechanism of the novel surface‐directed reaction selectivity is elucidated by extensive density functional theory (DFT) calculations. Our study paves the way for high selective synthesis of polycyclic conjugated hydrocarbons with non‐benzenoid rings.