chapter 2 palladium catalysts in suzuki cross- coupling reaction
chapter 2 palladium catalysts in suzuki cross- coupling reaction
chapter 2 palladium catalysts in suzuki cross- coupling reaction
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agglomerates dur<strong>in</strong>g dissolution/re-precipitation processes on the zeolite surface and<br />
water from the zeolite will be released <strong>in</strong> a timely and localized manner (slowly) s<strong>in</strong>ce it<br />
is <strong>in</strong> the pores, whereas water alone (without added zeolite) reacts <strong>in</strong> an uncontrolled<br />
way.<br />
In order to check whether the coupl<strong>in</strong>g <strong>reaction</strong>s were catalyzed<br />
heterogeneously or not, the <strong>reaction</strong> was carried out with addition of 30,000 molar<br />
equivalent of an <strong>in</strong>soluble <strong>cross</strong>-l<strong>in</strong>ked poly(v<strong>in</strong>yl pyrid<strong>in</strong>e) polymer (PVPy) under<br />
optimized condition. After 4 h of <strong>reaction</strong>, only 20% coupl<strong>in</strong>g product was obta<strong>in</strong>ed,<br />
<strong>in</strong>dicat<strong>in</strong>g that PVPy greatly reduced the activity of the catalyst by strongly<br />
coord<strong>in</strong>at<strong>in</strong>g the soluble Pd(II) species while rema<strong>in</strong><strong>in</strong>g <strong>in</strong>ert towards the solid Pd.<br />
Therefore, if the <strong>reaction</strong> was performed by heterogeneous catalyst, no change <strong>in</strong> the<br />
<strong>reaction</strong> progress should be expected. Consequently, the coupl<strong>in</strong>g <strong>reaction</strong>s were proven<br />
to be catalyzed by the dissolved Pd species leached from the Pd-NaY catalyst.<br />
5.1.2. Pd(NH3)4 2+ -loaded NaY type Zeolite Catalyzed Suzuki Cross-<br />
Coupl<strong>in</strong>g Reaction of Aryl Chlorides<br />
The Suzuki <strong>reaction</strong> of variety aryl halides with PhB(OH)2 were <strong>in</strong>vestigated<br />
under the optimal conditions determ<strong>in</strong>ed (2 equiv. of PhB(OH)2, 2 equiv. sodium<br />
ethoxide, 1 equiv. Bu4NBr, 3g NaY zeolite and, for 5 m<strong>in</strong>utes, under aerobic<br />
conditions). The results obta<strong>in</strong>ed with activated aryl chlorides were quite good at 140<br />
°C (Table 5.6). However, at 120 o C, the catalyst reserved its high activity on <strong>reaction</strong>s<br />
of 4-chloroacetophenone and 4-nitrobenzene (entry 1, 4). On the other hand, moderate<br />
yields were obta<strong>in</strong>ed for other p-substituted chloroarenes (entry 2, 3). The result was not<br />
satisfactory <strong>in</strong> the case of 2-substituted aryl chlorides (entry 5).<br />
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