On-surface cyclodehydrogenation reaction pathway determined by selective molecular deuterations

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2021-12-08
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Ma, Chuanxu
Xiao, Zhongcan
Bonnesen, Peter V.
Liang, Liangbo
Puretzky, Alexander A.
Huang, Jingsong
Kolmer, Marek
Sumpter, Bobby G.
Lu, Wenchang
Hong, Kunlun
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Iowa State University Digital Repository, Ames IA (United States)
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Ames National Laboratory
Abstract
Understanding the reaction mechanisms of dehydrogenative C-aryl-C-aryl coupling is the key to directed formation of pi-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 C-aryl-C-aryl coupling is revealed by monitoring the ratios of gas-phase by-products of H-2, HD, and D-2 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.
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This article is published as Ma, Chuanxu, Zhongcan Xiao, Peter V. Bonnesen, Liangbo Liang, Alexander A. Puretzky, Jingsong Huang, Marek Kolmer et al. "On-surface cyclodehydrogenation reaction pathway determined by selective molecular deuterations." Chemical Science 12, no. 47 (2021): 15637-15644. DOI: 10.1039/D1SC04908A. Copyright 2021 The Author(s). Attribution-NonCommercial 3.0 Unported (CC BY-NC 3.0). DOE Contract Number(s): AC05-00OR22725; AC02-07CH11358; 12074359; 22002149; N00014-20-1-2302; N00014-16-1-3153; OCI-1036215. Posted with permission.
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