Diradical Mechanisms for the Cycloaddition Reactions of 1,3-Butadiene, Benzene, Thiophene, Ethylene, and Acetylene on a Si(111)-7×7 Surface

Abstract

The cycloaddition chemistry of several representative unsaturated hydrocarbons (1,3-butadiene, benzene, ethylene, and acetylene) and a heterocyclic aromatic (thiophene) on a Si(111)-7x7 surface has been explored by means of density functional cluster model calculations. It is shown that (i) 1,3-butadiene, benzene, and thiophene can undergo both [4+2]-like and [2+2]-like cycloadditions onto a rest atom-adatom pair, with the former process being favored over the latter both thermodynamically and kinetically; (ii) ethylene and acetylene undergo [2+2] cycloaddition-like chemisorptions onto a rest atom-adatom pair; and (iii) all of these reactions adopt diradical mechanisms. This is in contrast to the [4+2] cycloaddition-like chemisorptions of conjugated dienes on a Si(100) surface and to the prototype [4+2] cycloadditions in organic chemistry, which were believed to adopt concerted reaction pathways. Of particular interest is the [4+2]-like cycloaddition of s-trans-1,3-butadiene, whose stereochemistry is retained during its chemisorption on the Si(111) surface.

Chemical manipulation of multifunctional hydrocarbons on silicon surfaces

“…[281]. c 2007, The American Chemical Society such as acrylonitrile [315], 1,3-cyclohexadiene [300], and 1,3-butadiene [307] even more than these reactions are favored on Si(100)-2×1. Interestingly, the asymmetric and highly polar acrylonitrile [315] that forms a [4 + 2]-product of the type Si-CH 2 -CH=C=N-Si confirmed by a vibrational band ν C=C=N = 2028 cm −1 [378], can bind in two different ways with respect to the adatom-rest atom pair: with the nitrogen bound to adatom and with the nitrogen bound to the rest atom.…”

The role of a precursor state in thiophene chemisorption on Si(111)–7×7

“…Finally, it is noted that a previous theoretical investigation of thiophene chemisorption on this surface, using a Si 16 H 18 cluster or unit cell fragment to model the surface [13], demonstrated that chemisorption is stepwise and that there are two activation energy barriers associated with the process. The first barrier was calculated to be 0.234 eV, above the energy of the isolated molecule/surface system, and the second barrier was calculated to be 0.061 eV above the energy of an intermediate state.…”

“…The first STM investigation of thiophene adsorbed onto the Si(111)-7×7 surface noted that at low coverage, thiophene does not distribute randomly over the available bonding sites but chemisorbs preferentially on edge adatoms in the faulted half of the unit cell [13]. This site preference has been observed for other simple aromatic molecules on the 7×7 surface, including benzene [3] and chlorobenzene [14].…”

Functionalization of Single-Wall Carbon Nanotubes: An Assessment of Computational Methods

“…In another study, Lu et al [30] found a binding energy of -31.3 kcal/mol, considering a 6-layer tube, while first principles calculations were also performed [31]. Most recently, sidewall epoxidation of SWCNTs was studied with ONIOM [32].…”