Bond selectivity in electron-induced reaction due to directed recoil on an anisotropic substrate

Abstract

Bond-selective reaction is central to heterogeneous catalysis. In heterogeneous catalysis, selectivity is found to depend on the chemical nature and morphology of the substrate. Here, however, we show a high degree of bond selectivity dependent only on adsorbate bond alignment. The system studied is the electron-induced reaction of meta-diiodobenzene physisorbed on Cu(110). Of the adsorbate’s C-I bonds, C-I aligned ‘Along’ the copper row dissociates in 99.3% of the cases giving surface reaction, whereas C-I bond aligned ‘Across’ the rows dissociates in only 0.7% of the cases. A two-electronic-state molecular dynamics model attributes reaction to an initial transition to a repulsive state of an Along C-I, followed by directed recoil of C towards a Cu atom of the same row, forming C-Cu. A similar impulse on an Across C-I gives directed C that, moving across rows, does not encounter a Cu atom and hence exhibits markedly less reaction.

Generation and Characterization of a meta-Aryne on Cu and NaCl Surfaces

“…This is not a surface catalytic effect, but it demonstrates that energy barriers for reactions might be lowered by accessing ionic states of molecules on insulating substrates. 38 Similar to the case of meta-DIB on Cu(110), 6,7 we have observed two possibilities: C−Br bonds break either one at a time with 5a as an intermediate or both C−Br bonds with a single voltage pulse. An example of the former is illustrated by manipulation of the molecule on the left-hand side in Figure 2d to Figure 2e.…”

“…Depending on the initial adsorption geometry, both pathways are possible for meta-DIB. 6,7 Alternatively to electronic excitation, cleavage of the C−I bonds can be triggered by vibrational excitation. 3 In contrast to above-mentioned results on metal surfaces, both ortho-(1, ref 4) and para-arynes (2, ref 5) are stabilized on insulating surfaces (Scheme 1).…”

“…Arynes are important reactive intermediates in chemical synthesis and have been recently generated on-surface from the corresponding dihalogenated aromatic precursors by cleavage of two C–X bonds (X = Br, I). − In general, aromatic hydrocarbons substituted with halogens (Br or I) in respective positions of a benzene ring serve as molecular precursors of arynes. The carbon–halogen bonds act as predetermined breaking points that can be cleaved by means of atomic manipulation.…”

“…It has been shown that generation of arynes from physisorbed diiodobenzene (DIB) precursor molecules adsorbed on metal surfaces leads to bond formation to the metal (chemisorption). − ,− Upon electronic excitation by tunneling electrons, C–I bonds break one at a time for para -DIB, but a single electron induces cleavage of both C–I bonds in ortho -DIB . This difference can be rationalized by the spatial extent of the antibonding orbital that is temporarily occupied upon electron tunneling.…”

Thermal- vs Light-Induced On-Surface Polymerization

“…Chemical bonds within adsorbed molecules have been dissociated using either the STM tip, , heat, or light or by a combination of voltage pulses from a STM tip and light. , The subsequent synthesis of covalently linked nanostructures is achieved by thermal activation or without heating (i.e., at RT) in the case of photoactivated species . The crucial role of species diffusion has been highlighted by exploring photodriven Glaser coupling reactions on different (111) metal surfaces .…”