Cross-Coupling Reactions of Alkenylsilanolates. Investigation of the Mechanism and Identification of Key Intermediates through Kinetic Analysis

The mechanism of the fluoride-free, palladium-catalyzed cross-coupling reaction of potassium (E)-heptenyldimethylsilanolate, K⁺(E)-1 ^-, with 2-iodothiophene has been investigated through kinetic analysis. The order of each component was determined by plotting the initial rates of the reaction against concentration. These data provided a mechanistic picture which involves a fast and irreversible oxidative insertion of palladium into the aryl iodide and a subsequent intramolecular transmetalation step from a complex containing a silicon-oxygen-palladium linkage. First-order behavior at low concentrations of silanolate with excess palladium(0) complex supports the formation of this complex as the turnover-limiting step. The change to zeroth-order dependence on silanolate at high concentrations is consistent with the intramolecular transmetalation becoming the turnover-limiting step.