Heterogeneous Suzuki reactions catalyzed by Pd(0)–Y zeolite

Abstract

Abstract-The Pd(0)-Y zeolite showed high activity in the Suzuki cross-coupling reactions of aryl bromides without added ligands. The type of base and organic solvent were found to be critical for the efficiency of the reaction. The presence of water was essential within the reaction medium. The coupling reactions occurred on the external surface of the zeolite. The catalyst is reusable.

Pd-loaded NaY zeolite as a highly active catalyst for ligandless Suzuki–Miyaura reactions of aryl halides at low Pd loadings under aerobic conditions

“…Pd-loaded NaY catalysts evidently worked at very high TONs, and we already showed that the catalyst can be re-used in the SM reactions of aryl bromides at room temperature with Pd concentration of 2.5 mol% after regeneration [23,24]. Nevertheless, we have determined in this study that the catalyst is not quite re-usable at low Pd loadings.…”

“…Alkali carbonates were the only bases screened in this study since they had been marked, previously, as being the most suitable base types for the SM coupling activity of palladium-loaded NaY zeolites [23,24]. In this study, sodium carbonate was observed to be the most efficient base when the reactions were performed in a DMF/water mixture (1/1).…”

“…Furthermore, the presence of inherent negative sites may lead to better dispersion of the cationic Pd units by ion exchange. Hence, Pdloaded zeolites were demonstrated to be highly active catalysts for the cross coupling of alkenyl halides with arylboronic acids [19], ␣-arylation of malonate [20], Heck [21], amination [22], Suzuki-Miyaura [23][24][25], and Sonogashira [26] reactions.…”

“…We reported previously that Pd-loaded NaY zeolites were highly active and re-usable catalysts in Suzuki-Miyaura crosscoupling reactions of aryl bromides at room temperature [23,24]. Nevertheless, the method required high Pd loadings (typically 2.5 mol%) for effective coupling.…”

“…In our previous report, we showed that this catalyst was inactive for the SM coupling reaction of bromoarenes at room temperature in the presence of an alkali carbonate base, in an N,N-dimethylformamide (DMF)/water mixture (1/1), while its air calcined or reduced forms were highly active under the identical reaction conditions [23,24]. Nevertheless, we noticed in this study that the Pd(NH 3 ) 4 2+ -loaded NaY shows very high SM coupling activity at the reaction temperature of 100 • C. Inactiv- ity of the Pd(NH 3 ) 4 2+ -NaY catalyst at room temperature could be associated with the inability of the palladium to reduce its active zero-valent form at the lower temperature.…”