Density functional theory B3LYP/6-31G* (except W with LanL2DZ basis set) has been employed to explore the mechanism of thermolysis of 2H-azaphosphirene complex to nitrilium phosphanylide complex, which could react with alkyne to yield 2H-1,2-azaphosphole complex. The obtained results indicate that the ring-opening reaction of 2H-azaphosphirene complex to phosphinidene is the rate-controlling one, which needs to overcome 84.3 kJ•mol^－1 energy barrier, and then the produced phosphinidene complex could react with cyanogens to yield nitrilium phosphanylide complex, which could further react with alkyne to generate the thermodynamically stable product 2H-1,2-azaphosphole complex. In addition, the catalytic effect of W(CO)₅ and substitution effect on the reaction mechanisms and reaction barriers have also been considered.

Key words: 2H-azaphosphirene complex, phosphinidene, nitrilium phosphanylide, cycloaddition, density functional theory (DFT)