Abstract: The cycloaddition reaction of silylene(SiH₂) and C₆₀ have been studied by using the semi-empiri- cal method AM1, a reasonable mechanism of the reaction has been suggested. All the geometry of the sta- tionary points on the reaction path have been optimized by energy gradient technique and the transition states were characterized by vibration frequency analysis. The calculation results show that the reaction mechanism is different between 6-6 and 6-5 bond addition. The 6-6 bond cycloaddition reaction proceedvia two steps: (1) Silylene and C₆₀ form an intermediate complex; (2) The closed isomer of C₆₀SiH₂ is formedvia TSfrom intermediate complex. After being corrected by zero-point energies the barriers is 0.45 kJ·mol^-1. While the 6-5 cycloaddition reaction is of three steps: (1) An intermediate complex is formed from the reactants C₆₀ and SiH₂ with no barrier. (2) The closed intermediate is formedvia TS(Ⅰ). After being corrected by zero-point energies the barriers is 9.19 kJ·mol^-1. (3) The opened isomer of C₆₀SiH₂ is producedvia TS(Ⅱ) with the barrier of 4.33 kJ·mol^-1. The reasons that silylene cycloaddition should take place across 6-6 bond rather than 6-5 bond of C₆₀ are explained from the reaction mechanism and kinetic factors.

Key words: C₆₀, Silylene, Cycloaddition, TS, AM1