# On-surface synthesis platform for highly branched oligomers based on sequential C—C coupling and C—H activation of carbenes

## TL;DR

This paper introduces a new on-surface synthesis method using carbenes to create highly branched nanostructures with unique shapes.

## Contribution

The study presents a novel on-surface synthesis strategy using carbene C−H activation to design branched zero-dimensional oligomers.

## Key findings

- Highly symmetric branched oligomers were synthesized via C−C coupling and C−H activation of carbenes on a metal surface.
- Lower symmetry branched oligomers were formed through cyclodehydrogenation of symmetric structures.
- The method combines experimental imaging and theoretical modeling to confirm the synthesis pathway.

## Abstract

On-surface synthesis is an emerging field for fabricating low-dimensional nanostructures. While carbenes are versatile reactive intermediates in solution-phase organic synthesis, they have rarely been explored in on-surface synthesis. Here, we demonstrate the versatility of carbenes in synthesizing highly branched zero-dimensional oligomers with distinct structures on a metal surface by combining bond-resolved scanning tunneling microscopy imaging, manipulation, X-ray photoelectron spectroscopy, surface infrared spectroscopy, and ab initio theoretical modeling. We synthesize highly symmetric branched oligomers through the C−C coupling of two carbene molecules to form a core of oligomers, followed by C−H activation of the core with up to four additional carbene molecules to create branches. Branched oligomers of lower symmetry are formed through cyclodehydrogenation of the highly symmetric oligomers. Our on-surface synthetic strategy based on C−H activation of carbene building blocks provides a platform for the design and synthesis of highly branched zero-dimensional oligomers with distinct structures.

While carbenes are versatile reactive intermediates in solution-phase organic synthesis, they have rarely been explored in on-surface synthesis. Here, the authors demonstrate the versatility of carbenes in synthesizing highly branched zero-dimensional oligomers with distinct structures on a metal surface.