chapter 2 palladium catalysts in suzuki cross- coupling reaction

clay materials was found to be an effective method for preparing active catalysts in
Suzuki cross coupling reactions. They also tested the reusability of the catalyst. It was
observed that after three catalytic cycles the catalyst lost some activity after each reuse
(Ruiz et al. 2006).
Corma et al. tested bifunctional (palladium and basic sites) sepiolites clay for
their catalytic activities for the Heck and Suzuki reactions in the absence of any
extrinsic base at 145 °C. However, irreversible depletion of the basic sites of the
sepiolite was considered to be responsible for the deactivation of the catalyst (Corma et
al. 2004).
Shimizu et al. reported that [Pd(NH3)4] +2 -exchanged sepiolite clay was highly
active for Suzuki reactions of 4-bromophenol with phenylboronic acid or sodium
tetraphenylborate in water (Shimizu et al. 2004).
The recyclable nanopalladium particles supported on layered double hydroxide
(LDH) were designed and developed by a simple ion-exchange technique following
reduction processes. This heterogeneous palladium catalyst showed high activity for
Heck-, Suzuki-, Sonogashira-, and Stille-type coupling reactions of chloroarenes to
afford good to excellent yields of coupling products (Choudary et al. 2002).
Researchers synthesized palladium hollow spheres showing good catalytic
activities in Suzuki cross coupling reactions of iodothiophene and phenylboronic acid
and can be reused at least for 7 cycles at 78 °C with no apparent leaching (Kim et al.
2002). They reported that Pd shell is not active enough to catalyze the reaction of aryl
chloride (Figure 3.12).
Silica
sphere
HF, Etching
palladium hollow spheres
Figure 3.12. Preparation of palladium hollow spheres
(Source: Kim et al. 2002)
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