Mechanism of olefin cyclopropanation by diazomethane catalyzed by palladium dicarboxylates. A density functional study

The reaction of diazomethane with ethylene in the presence of palladium dif ormate has been studied through density funcional calculations. Several mec hanistic paths leading to the formation of cyclopropane have been studied. The results obtained show that the reaction of palladium diformate with dia zomethane is more favorable than the reaction with ethylene. The reaction w ith diazomethane may lead to two different isomeric complexes: a methylene- inserted complex and a palladium-carbene complex. Insertion of methylene is the most favorable process, but the resulting complex is not suitable for cyclopropanation. The reaction with two additional diazomethane molecules m akes the formation of the bismethylene-inserted palladium-carbene complex f avorable. Attack of ethylene on this palladium-carbene complex leads to the formation of cyclopropane.