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

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Abstract
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.