chapter 2 palladium catalysts in suzuki cross- coupling reaction

utilized them in Heck and Suzuki coupling reactions of iodo-, bromo- and chloroarenes
(Figure 3.11). The heterogeneous catalyst was reusable many times (Gurbuz et al.
2003).
In 2003, Paul and Clark used a novel silica-supported palladium catalyst, 35
(Figure 3.11), for Suzuki reactions of aryl and polyaryl bromides with phenylboronic
acid (Table 3.1, entry 9). The key features of the catalyst included rapid reactions,
excellent catalyst recyclability and total stability under reaction conditions. The catalyst
which has a very low loading of palladium was defined as completely heterogeneous
and highly stable under reaction conditions (Paul and Clark 2003).
Si O Si
N
N
Cl Pd Cl
N
N
O
Cl
Si O Si O Si
34
Si
N
N
Pd Cl
N
N
AcO
OAc
Pd
O O
N
Silica
35
Si
N
O
CH 3
Figure 3.11. The immobilized Pd(II) species on silica supports
Clays are also special inorganic solids since they have well-defined structures
and pores with molecular dimensions, which can solvate the adsorbed molecules and
provide solvent-like environments (Smith and Nontheisz 1999).
Varma et al. reported PdCl2/tetraphenylphosphonium bromide-intercalated clay
as a heterogeneous catalyst for Suzuki coupling of aryl bromides and iodides (Varma et
al. 1999, Varma and Naicker 1999a, Varma and Naicker 1999b).
The deposition of palladium salts on hydrotalcite which is a naturally occurring
mineral of the layered double hydroxide family that constitutes a major class of anionic
35