Sonogashira Synthesis

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Since suitable crystals for X-ray single crystal analysis was not obtained, to have reliable structural information, HR-TEM analysis of the product was carried out. The average size of the assembly calculated from HR-TEM measurement is found to be 2.8 nm which is in good agreement with the size of the previously reported Pd6L8 assembly where L is the non N-methylated (2.5nm, Fig. 2).9
As first step, to explore the catalytic activity of 1 in copper and phosphine free Sonogashira coupling reaction in water, we optimised the conditions for the reaction between p-Iodonitrobenzene and phenyl acetylene in absence of copper(I) salt. It was observed that at a temperature of 50°C (among 25°C, 50°C and 80°C) the bases used, piperidine and Et3N (among NaHCO3, Na2CO3, K2CO3, KOH, Et3N and piperidine) give high yield under aerobic conditions (Table 1). Secondly, parallel reaction between phenyl acetylene and p-Iodonitrobenzene were
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The results are summarised in Table 3. The corresponding products were obtained in good to excellent yields in 12-20 hrs (Table 3). Aryl halides with electron-withdrawing substituent’s, such as –NO2, (Table 3, Entries 2 and 9) and fluoro, (Table 3, Entry 3) gave excellent yields, while aryl halides with electron-donating groups, such as methyl and -OMe (Table 3, Entries 6, 7 and 8) gave the coupling products in slightly lower yield. In addition to aryl iodides, aryl bromides were also investigated for the Sonogashira reaction by catalyst 1. However, it was observed that, even after providing a higher temperature (80°C) and extended reaction time (36h), the reaction does not go to completion. It gives only 30% product yield for 4-Bromotoluene and 32% yield for 4-Bromoanisole under vigorous conditions (Table 3, Entries 10 and

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