Origin and consequences of aromatic back-bonding at a transition metal surface: Benzyne on Ir{100}

Abstract

Articles you may be interested inA DFT study of the NO dissociation on gold surfaces doped with transition metals J. Chem. Phys. 138, 074701 (2013); 10.1063/1.4790602 Trends in C-O and C-N bond formations over transition metal surfaces: An insight into kinetic sensitivity in catalytic reactionsRecent low energy electron diffraction experiments have shown that partial dissociation of benzene at the Ir͕100͖ surface yields an ordered overlayer of ortho-benzyne radicals (C 6 H 4 ) with ring-planes inclined at 47.2°to the normal. The primary molecule-surface interaction may be attributed to bonds between radical C and surface Ir atoms, but this characteristic alone does not uniquely constrain the adsorbate to the observed orientation. Through first-principles density functional theory which gives good agreement with the experimental structure, we now demonstrate that the molecular tilt arises due to interaction of the aromatic orbitals with the surface d orbitals, and not because of any dispersive intermolecular forces.

Aromatic adsorption on metals via first-principles density functional theory

“…Stoichiometric considerations strongly imply that the remaining surface species is benzyne rather than phenyl, and indeed quantitative analysis of the LEED-IV spectra indicates the ortho form of the molecule, bonding through the dehydrogenated C atoms and inclined with its ring plane at approximately 47 • to the surface. Subsequent first-principles calculations by Yamagishi et al (2002Yamagishi et al ( , 2003 yielded an adsorption geometry (figure 7) in remarkable agreement with the experimental observation (e.g. tilt angle 48 • ) and analysis of the electronic structure demonstrated that adsorbate-substrate binding was due in part to σ bonds involving the dehydrogenated C atoms, and in part due to bonding through the π orbitals of the aromatic ring.…”

“…Subsequent first-principles calculations by Yamagishi et al (2002Yamagishi et al ( , 2003 yielded an adsorption geometry (figure 7) in remarkable agreement with the experimental observation (e.g. tilt angle 48…”

Benzene adsorption and oxidation on Ir(111)

“…These species probably have a BE that is very similar to benzene(I) and they are therefore not resolved in the C 1s spectra. A mechanism involving C 6 H x species is in line with the observations of Johnson et al [31] and Yamagishi et al [32], who found a stable, tilted (47°) benzyne (C 6 H 4 ) intermediate on Ir (100), which forms upon benzene adsorption at 465 K, and forms an ordered c-(2 · 4) overlayer.…”

On the factors that control the reactivity of meta-benzynes

“…However, biradicals with similar or identical DAS for the minimum energy structures still can have very different DE 2.30 values. In particular, 4-cyano-3,5-didehydropyridinium cation (4) and 2-cyano-3,5-didehydropyridinium cation (10) (with the same EA 2.30 (6.97 eV) and almost identical S-T splittings (À22.1 and À23.0 kcal mol À1 , respectively) and DAS (1.52 and 1.50 Å, respectively)) have quite different DE 2.30 (8.5 and 5.0 kcal mol À1 for 10 and 4, respectively; Table 1). Finally, this reactivity controlling parameter explains why 4 reacts with cyclohexane signicantly faster than 10 (Eff.…”

“…Arynes 1,2 play a pivotal role in the biological activity of enediyne cytostatics, [3][4][5] combustion reactions, [6][7][8] heterogeneous catalysis, 9,10 as well as nucleophilic addition and cycloaddition reactions in organic synthesis. [11][12][13][14] Hence, they have been the subject of many experimental and computational studies for the last few decades.…”