Imaging single-molecule reaction intermediates stabilized by surface dissipation and entropy

Abstract

Chemical transformations at the interface between solid/liquid or solid/gaseous phases of matter lie at the heart of key industrial-scale manufacturing processes. A comprehensive study of the molecular energetics and conformational dynamics that underlie these transformations is often limited to ensemble-averaging analytical techniques. Here we report the detailed investigation of a surface-catalysed cross-coupling and sequential cyclization cascade of 1,2-bis(2-ethynyl phenyl)ethyne on Ag(100). Using non-contact atomic force microscopy, we imaged the single-bond-resolved chemical structure of transient metastable intermediates. Theoretical simulations indicate that the kinetic stabilization of experimentally observable intermediates is determined not only by the potential-energy landscape, but also by selective energy dissipation to the substrate and entropic changes associated with key transformations along the reaction pathway. The microscopic insights gained here pave the way for the rational design and control of complex organic reactions at the surface of heterogeneous catalysts.

On‐Surface Formation of Cumulene by Dehalogenative Homocoupling of Alkenyl gem‐Dibromides

“…47,48 The projector augmented wave method was used to describe the interaction between ions and electrons, 49,50 and the PerdewBurke-Ernzerhof generalized gradient approximation exchange−correlation functional was employed. 51 Van der Waals corrections to the PBE density functional were also included using the DFT-D3 method of Grimme.…”

Mechanistic Insights into Surface-Supported Chemical Reactions

“…The prowess of single molecule bond-resolved AFM measurements is shown in recent studies on enediyne cyclization reactions [4,29,35,36,54]. These reactions are more complex than the reactions presented above, as multiple chemical bonds are affected in such transformations.…”

“…These transformations yield a plethora of different chemical species that were analyzed using bond-resolved AFM using CO-functionalized tips [36]. The major focus of this study was put on the dimeric species, which are formed through monomer coupling by formation of covalent bonds between the terminal alkyne groups of two precursor molecules (1).…”

“…These reactions are more complex than the reactions presented above, as multiple chemical bonds are affected in such transformations. Furthermore, different reaction pathways can occur leading to a complex reaction mixture that needs to be analyzed molecule by molecule [4,36,54,55].…”

Tracking On-Surface Chemistry with Atomic Precision

“…By using nc-AFM, the team was able to visualize the ring-expanded molecules, clearly revealing the cleaved bond and giving indisputable evidence of the transformation. Other elegant examples of isomers and intramolecular transformations analyzed with nc-AFM include the subtle differentiation of cumulene and aryne tautomers in a PAH, 28 cyclization of triangular dehydrobenzoannulene, 22 reactions of oligo-(phenylene-1,2-ethynylenes) 27,29 (see Figure 1, b), sulfur elimination from diphenanthrothiophene, 30 and conformational changes in tetraphenylporphyrins 31 and dibenzo[a,h]thianthrene. 32 The last three examples show that nc-AFM can even be used on molecules that are not completely planar, although at the expense of losing contrast in regions that are closer to the surface.…”