chapter 2 palladium catalysts in suzuki cross- coupling reaction

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.
In order to check whether the coupling reactions were catalyzed
heterogeneously or not, the reaction was carried out with addition of 30,000 molar
equivalent of an insoluble cross-linked poly(vinyl pyridine) polymer (PVPy) under
optimized condition. After 4 h of reaction, only 20% coupling product was obtained,
indicating that PVPy greatly reduced the activity of the catalyst by strongly
coordinating the soluble Pd(II) species while remaining inert towards the solid Pd.
Therefore, if the reaction was performed by heterogeneous catalyst, no change in the
reaction progress should be expected. Consequently, the coupling reactions were proven
to be catalyzed by the dissolved Pd species leached from the Pd-NaY catalyst.
5.1.2. Pd(NH3)4 2+ -loaded NaY type Zeolite Catalyzed Suzuki Cross-
Coupling Reaction of Aryl Chlorides
The Suzuki reaction of variety aryl halides with PhB(OH)2 were investigated
under the optimal conditions determined (2 equiv. of PhB(OH)2, 2 equiv. sodium
ethoxide, 1 equiv. Bu4NBr, 3g NaY zeolite and, for 5 minutes, under aerobic
conditions). The results obtained with activated aryl chlorides were quite good at 140
°C (Table 5.6). However, at 120 o C, the catalyst reserved its high activity on reactions
of 4-chloroacetophenone and 4-nitrobenzene (entry 1, 4). On the other hand, moderate
yields were obtained for other p-substituted chloroarenes (entry 2, 3). The result was not
satisfactory in the case of 2-substituted aryl chlorides (entry 5).
60