title: [2+2] Cycloaddition reactions of ethylene derivatives with the Si(100)-2 x 1 surface: a theoretical study.
abstract: Possible mechanisms of the [2+2] cycloaddition reactions of ethylene (1), propylene (2), vinyl chloride (3), and styrene (4) with the Si(100)-2 x 1 surface have been investigated by theoretical calculations with the unrestricted density functional theory (DFT) and the second-order Møller-Plesset perturbation theory (MP2). Facile occurrence of the studied reactions is supported by the low activation energies (2.45-5.76 kcal/mol) in the rate-determining steps. The buckled Si(100) surface facilitates the reactions via the low-symmetric pathways. The reactions follow the diradical mechanism of thermal [2+2] cycloaddition reactions between pi-electron donors (the ethylene derivatives) and acceptors (the Si surface) through a pi-complex precursor and a singlet diradical intermediate. The influence of substituents on the relative reactivity takes a qualitative sequence of 1 < 2 < 3 < 4. The natural bond orbital (NBO) analysis and the released heat of some model reactions suggest that the relative reactivity might be partially understood by the pi-electron-donating abilities of the substituent to stabilize the radical centers at the transition states of the rate-determining steps.
authors.affiliation: Department of Chemistry, Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry of MOE, Nanjing University, Nanjing, 210093, PR China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Wang
authors.forename: Jing
authors.initials: J
authors.lastname: Ma
authors.forename: Satoshi
authors.initials: S
authors.lastname: Inagaki
authors.forename: Yong
authors.initials: Y
authors.lastname: Pei