Highly Efficient On-surface Synthesis of Fused N-heterocyclic derivatives

The synthesis of N-fused heterocycles is a crucial element in organic chemistry. However, it involves multiple steps that add complexity and reduce overall yields. Here, we introduce the high-yield on-surface synthesis of N-heterocyclic compounds employing the intramolecular hydroamination of alkyne-functionalized molecular precursors under mild thermal conditions in an ultra-high vacuum environment on an Au(111) surface. This method offers an efficient preparation of two discrete N-heterocyclic derivatives using a single gold(0)-atom catalyst. Notably, the synthesis introduces two pyrrole groups into quinoidal-based precursor, enabling the formation of two fused pyrrolo-benzoquinonediimine compounds with tailored electronic band-gap not achievable in solution chemistry. To analyze the resulting reaction products, we utilized scanning tunneling microscopy and non-contact atomic force microscopy with single bond resolution, comparing these products to those obtained through traditional solution methods. We further performed computational studies to elucidate detailed mechanistic insights into the on-surface reaction course.