On-Surface Debromination of C₆Br₆: C₆ Ring versus C₆ Chain

Abstract

Carbon allotropes comprising sp-hybridized carbon atoms have been investigated for decades for their molecular structure. One of the unsolved mysteries is whether they should take a linear or cyclic configuration in condensed phases due to the lack of atomistic characterizations. Herein, we designed a molecule with a C6 skeleton as a model system to address this issue, which was achieved by eliminating Br atoms from hexabromobenzene (C6Br6) molecule on the Ag(111) substrate via thermal treatment. It is found that the C6 ring intermediate resulting from complete debromination is energetically unstable at room temperature based on theoretical calculations. It subsequently transforms into the C6 polyynic chain via a ring-opening process and ultimately polymerizes into the organometallic polyyne, whose triyne structural unit is revealed by bond-resolved noncontact atomic force microscopy. Theoretical calculations demonstrated an energetically favorable pathway in which the ring-opening process occurs after complete debromination of C6Br6. Our study provides a platform for the synthesis of elusive carbon-rich materials.

Real-space visualization of sequential debromination of polybrominated benzenes on Ag(111)

“…3e), where individual ones could be identified as indicated by the green contours. As inspired by the previous studies 4,12 and compared with STM observations, 4,6 we attributed the three central bright protrusions to Ag atoms, connecting three neighboring dibrominated components. The large-scale STM images of islands composed of organometallic dimers and trimers are also provided in Fig.…”

“…1 It has also attracted great attention from the surface science community as a versatile strategy to construct C-C bonds and corresponding carbon-based nanoarchitectures via on-surface synthesis. 2 Moreover, by means of in situ characterization techniques, such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM), 3 sets of intermediates, generally classified into surface-stabilized radicals and organometallic intermediates, have been successfully captured on surfaces and visualized in real space, [4][5][6] which is usually a great challenge in traditional organic synthetic chemistry. As early as 2000, Hla et al reported deiodination and sequential coupling processes (i.e., Ullmann reaction) on surface with all elementary steps controllably triggered by STM tip manipulations and intermediates captured.…”

High-Yield Production of Quantum Corrals in a Surface Reconstruction Pattern

“…Second, the herringbone reconstruction of Au(111) can be lifted by adsorbate-induced stress modification, , which in turn makes an impact on the molecular assembly . Third, Au(111) is the least reactive noble metal for Ullmann coupling that prevents the decomposition of organic skeletons before desorption. , In this study, we reveal that hot dosing a trace amount of HBB onto a preheated Au(111) surface results in QCs defined by barriers built from Br dot chain arrays. The chain arrays aggregate into highly stable QCs with an average pore size of 3.7 ± 0.1 nm, which is confined by triangular soliton walls formed from Au(111) surface reconstruction induced by the strong bonding of Br with thermal treatment.…”

“…To this end, we use hexabromobenzene (HBB) and Au(111) as the precursor and substrate to construct robust QCs with high-yield production (Scheme ). Our approach is based on the following experimental facts: First, the dehalogenation reaction is appealing for on-surface synthesis of covalently linked architectures with atomic precision. ,, The byproducts, Br adatoms, bind strongly on the Au(111) surface that can only be desorbed above 720 K in the absence of other species . Second, the herringbone reconstruction of Au(111) can be lifted by adsorbate-induced stress modification, , which in turn makes an impact on the molecular assembly .…”

Polymerization of Epoxides via Ring-Opening Coupling on Surfaces

“…For example, the heterocyclic ring-opening reactions, such as on-surface desulfurization of thiophene, − deconstruction of porphyrin and N -doped nanographene, and the ring-opening polymerization of melamine, have been reported to generate a variety of novel nanostructures. Recently, Gao et al reported a debromination ring-opening coordination reaction of hexabromobenzene to synthesize C6–Ag organometallic polyyne …”