chapter 2 palladium catalysts in suzuki cross- coupling reaction

CHAPTER 6
CONCLUSIONS
In this thesis study, Pd(NH3)4 2+ ion was easily loaded into the NaY zeolite.
Activity of catalyst was investigated over Suzuki coupling reactions of aryl bromides
and chlorides.
The Pd(NH3)4 2+ -loaded NaY zeolite was observed to activate the C-Cl bond of
the electron poor aryl chlorides in Suzuki reactions at low Pd concentrations in air
within minutes. The excess amounts of zeolite provided the necessary water for the
reaction when employed in as-received form. The results pointed out to a synergistic
effect due to use of the water-zeolite pair for the reaction. The underlying reasons for
the observed synergism seem to be complicated. However, the fact remains that the
presence of little amount of water was crucial for the activation of the reaction system.
In addition to water effect, the presence of excess amounts of zeolite in the reaction
medium had important roles. We thought that it might have retarded the transformation
of Pd to inactive Pd agglomerates during dissolution/re-precipitation processes on the
zeolite surface and water from the zeolite will be released in a timely and localized
manner (slowly) since it is in the pores, whereas water alone (without added zeolite)
reacts in an uncontrolled way.
Zeolite catalyst was also found highly active for Suzuki cross-coupling reactions
of various bromoarenes with arylboronic acids without added ligands. The reactions
were proceeded at very low Pd concentrations (0.01- 0.001% Pd). The presence of water
was essential within the reaction medium.
In both reactions of aryl chlorides and bromides, the catalyst was stable in air.
The commercial source of phenylboronic acid reagent was found to be highly effective
for the catalyst activity. Probably, variation types of impurities had different effects on
the catalyst activity.
It must also be noted that no dechlorination or self-coupling products were
produced by the reactions performed under the established conditions.
In the view of our results, the coupling reactions were seemed to be catalyzed by
the dissolved Pd species leached from the Pd-NaY catalyst. On the other hand, ICP-MS
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