title: Diradical mechanisms for the cycloaddition reactions of 1,3-butadiene, benzene, thiophene, ethylene, and acetylene on a Si(111)-7x7 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.
authors.affiliation: State Key Laboratory for Physical Chemistry of Solid Surfaces and Center for Theoretical Chemistry, Department of Chemistry, Xiamen University, Xiamen 361005, China. xinlu@xmu.edu.cn
authors.forename: Xin
authors.initials: X
authors.lastname: Lu
authors.forename: Xinlan
authors.initials: X
authors.lastname: Wang
authors.forename: Qinghong
authors.initials: Q
authors.lastname: Yuan
authors.forename: Qianer
authors.initials: Q
authors.lastname: Zhang