Density functional theoretical studies of [2+2] cycloaddition of simple transient silenes and germenes to ethylene, formaldehyde, and thioformaldehyde, and vibrational analysis of spectra of reactants and cyclic products

The cycloadditions of small unsaturated organic molecules, such as ethylene , formaldehyde, and thioformaldehyde, to simple silenes and their germanium analogues were studied by the density functional theory B3LYP/6-311G(d,p) method. The optimized geometry parameters, vibrational frequencies, and ene rgies of the ground states of the reactants and products and those of react ion transition states found were discussed. A lower reactivity of germenes than silenes in the reactions studied was predicted and a non-concerted two -step mechanism of [2+2] cycloadditions suggested.