2021 article

On-surface cyclodehydrogenation reaction pathway determined by selective molecular deuterations

Ma, C., Xiao, Z., Bonnesen, P. V., Liang, L., Puretzky, A. A., Huang, J., … Li, A.-P. (2021, November 16). CHEMICAL SCIENCE.

By: C. Ma*, Z. Xiao n, P. Bonnesen*, L. Liang*, A. Puretzky*, J. Huang*, M. Kolmer*, B. Sumpter* ...

Source: Web Of Science
Added: November 29, 2021

Understanding the reaction mechanisms of dehydrogenative Caryl-Caryl coupling is the key to directed formation of π-extended polycyclic aromatic hydrocarbons. Here we utilize isotopic labeling to identify the exact pathway of cyclodehydrogenation reaction in the on-surface synthesis of model atomically precise graphene nanoribbons (GNRs). Using selectively deuterated molecular precursors, we grow seven-atom-wide armchair GNRs on a Au(111) surface that display a specific hydrogen/deuterium (H/D) pattern with characteristic Raman modes. A distinct hydrogen shift across the fjord of Caryl-Caryl coupling is revealed by monitoring the ratios of gas-phase by-products of H2, HD, and D2 with in situ mass spectrometry. The identified reaction pathway consists of a conrotatory electrocyclization and a distinct [1,9]-sigmatropic D shift followed by H/D eliminations, which is further substantiated by nudged elastic band simulations. Our results not only clarify the cyclodehydrogenation process in GNR synthesis but also present a rational strategy for designing on-surface reactions towards nanographene structures with precise hydrogen/deuterium isotope labeling patterns.