[2+2] Cycloaddition reactions of ethylene derivatives with the Si(100)-2 x 1 surface: a theoretical study
Yong Wang1, Jing Ma, Satoshi Inagaki
1Department of Chemistry, Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry of MOE, Nanjing University, Nanjing, 210093, PR China.
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.
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