Theoretical Studies on the Reaction Mechanism for the Cycloaddition of Zwitterionic π-Allenyl Palladium Species: Substrate-Controlled Isomerization

Zwitterionic pi-allenyl palladium species are newly developed intermediates. A substrate-controlled step existed in the cycloaddition of zwitterionic pi-allenyl palladium species with tropsulfimides or tropones. With the assistance of previously experimental studies, zwitterionic allenyl/propargyl palladium species was provenly found by HRMS. Further DFT calculation studies show that zwitterionic pi-allenyl palladium species are generated through the oxidative addition of Pd(0), which can be promoted by Lewis acid like Yb(OTf)3, and the cycloaddition more likely undergoes through an outer sphere nucleophilic attack. The isomerization is caused by the difference of dissociation energy between the cycloaddition intermediation of tropsulfimides and tropones, forming the substrate-controlled specificity.