Experimental Chemistry II
Experiment A4: Palladium Catalysis: The Suzuki Reaction
In this experiment, the Suzuki reaction was performed using phenylboronic acid, p-iodophenol and Pd/C catalysis in potassium carbonate aqueous media to synthesize biphenyl-4-ol. The yield of final product was only 11.94% and the measured melting point was 170-175℃. Since the appearance of the product was significantly different from expected light tan color and the measured melting point was higher than literature value, the experimental synthesized product may not be the desire final product, biphenyl-4-ol, or may contain large amount of impurities.
The Suzuki reaction was reported in 1979 by Akira Suzuki and N. Miyaura. It is commonly referred to as the palladium-catalyzed cross coupling of aryl halides with organoboron reagents leading to the formation of sp2-sp2 carbon-carbon bonds.1 It is a powerful cross coupling method that allows for the synthesis of conjugated olefins, styrenes, and biphenyls. The purpose of this experiment was to perform a palladium/charcoal catalyzed Suzuki reaction using phenylboronic acid and p-iodophenol in potassium carbonate aqueous media to synthesize a biphenyl product, biphenyl-4-ol. The overall reaction is shown as:
The mechanism of the Suzuki reaction is best viewed from a generated catalytic cycle, which is shown below:
Figure 1: A generalized palladium catalytic cycle for the Suzuki reactio.2 This cycle states the Suzuki reaction is generally achieved by three steps: oxidatice addition, transmetalation and reductive elimination.2 Oxidative addition is the rate determining step of the catalytic cycle. The palladium catalyst couples with the p-iodophenol which results in an organopalladium complex. This complex is initially in the cis conformation but isomerizes to the trans conformation. Stereochemistry with vinyl halides are maintained, while inversion of stereochemistry happens...