A new, improved precatalyst for Suzuki-Miyaura cross-coupling reactions
palladium precatalysts , cross-coupling
Carbon-carbon bond formation is one of the most important reactions in organic chemistry, and the Suzuki-Miyaura cross-coupling reaction has become a forerunner in this area. Considerable research has been directed at the mechanistic aspects and synthetic utility of the reaction; however, little attention has been given to the formation of the putative PdL2 catalysts. Due to their high reactivities, these catalysts are typically difficult to store and therefore are often generated in situ in unknown yields and at unknown rates via any number of available palladium precursors. This thesis describes research directed towards determining the optimum conditions to quantitatively generate compounds of the type Pd(0)Ln (L = PMePh2, PPh3, PCy3, PMeBut2, PBut3, dppe, dppp, dppf) from Pd(h5-C5H5)(h3-1-Ph-C3H4). Pd(h5-C5H5)(h3-1-Ph-C3H4) has been found to be a superior precursor for synthesizing catalytically active PdL2 compounds due to its ease in handling and reactivity with tertiary phosphines. Furthermore, investigations into the role of water in the transmetallation step of the Suzuki-Miyaura reaction are presented. The research indicates that water is necessary to effect the transmetallation step when coupling [NBu4][PhBF3] with 4-bromotoluene in toluene; however, the amount of water above one equivalent has no significant effect on the rate or yield of the reaction.