Theoretical Study of the Cycloaddition Reaction Mechanisms of Cyclic Phosphenium Cation and Methyleneimine

The charge distribution of cyclic phosphenium cation and its mechanism of cycloaddition reaction with methyleneimine have been systematically investigated at the M06-2X/6-311++G** level of theory in order to better understand the reactivity for the valence isoelectronic species of cyclic carbene. The cyclic phosphenium cation acts as an electrophilic reagent, accepting the σ electrons of the methyleneimine in the first addition step to form an intermediate complex. The more positive charges on the phosphorus atom in the cyclic phosphenium cation, the more stable the complex formed. Double bond and conjugated system can reduce the positive charges on phosphorus, in turn stabilizes the cyclic phosphenium cation. Design usable and stable cyclic phosphenium cation through introduction of double bond and conjugated system, which will expand their applications in coordination chemistry and catalytic systems. The second step is the complex transforms to a spiro-heterocyclic product via a transition state, the complexes are more stable than the products.