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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CHAPTER 5<br />
RESULTS AND DISCUSSIONS<br />
In this thesis, activity of Pd(NH3)4 2+ -loaded NaY was <strong>in</strong>vestigated for Suzuki<br />
<strong>reaction</strong>s at low Pd concentrations.<br />
The Pd(NH3)4 2+ -loaded NaY type zeolite showed high activity <strong>in</strong> the Suzuki<br />
<strong>cross</strong>-coupl<strong>in</strong>g <strong>reaction</strong>s of less expensive aryl chlorides and bromides at low <strong>palladium</strong><br />
concentrations <strong>in</strong> air and with<strong>in</strong> very short <strong>reaction</strong> time. Turnover frequencies (TOF)<br />
and turnover number (TON) limits of the catalyst were also <strong>in</strong>vestigated.<br />
5.1. The Suzuki Reactions of Aryl Chlorides<br />
5.1.1. Pd-NaY Catalyzed Suzuki Reaction of 4-Chloroacetophenone<br />
with Phenylboronic Acid<br />
At the beg<strong>in</strong>n<strong>in</strong>g of our study, optimization was performed for Suzuki <strong>reaction</strong><br />
of 4-chloroacetophenone with phenylboronic acid over Pd(NH3)4 +2 modified zeolite<br />
conta<strong>in</strong><strong>in</strong>g 0.68% Pd (0.064 mmol Pd/g NaY zeolite) under an <strong>in</strong>ert atmosphere. The<br />
zeolite content of the <strong>reaction</strong> medium was brought to 1 g upon addition of NaY zeolite<br />
<strong>in</strong> an as-received form.<br />
In the course of optimization, the effect of tetrabutylammonium bromide<br />
(TBAB) additive and temperature was first <strong>in</strong>vestigated us<strong>in</strong>g Na2CO3 as a base <strong>in</strong> N,Ndimethylacetamide<br />
(DMA). Product formation was <strong>in</strong>creased from 36% to 46% by<br />
addition of 0.5 equivalent Bu4NBr <strong>in</strong>to <strong>reaction</strong> medium at 140 o C under <strong>in</strong>ert<br />
atmosphere (Table 5.1, entry1-2). Under this condition, it was observed that <strong>in</strong>creas<strong>in</strong>g<br />
the water content (DMA: water ratio of 9:1) lowered the yield to 14 % (entry 3). No<br />
activity was observed when the ratio was 1:1. A higher yield (57%) and conversions<br />
were obta<strong>in</strong>ed at 160 °C <strong>in</strong> the presence of Bu4NBr (Table 5.1, entry 4).<br />
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