Pd-leaching and Pd-removal in Pd/C-catalyzed Suzuki couplings

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

“…Therefore, if the reactions were catalyzed heterogeneously, no change in the reaction progress should be expected. This result is consistent with the previous findings that Pd-loaded zeolites and other supported Pd catalysts act as soluble Pd reservoirs for C C coupling reactions [21,[81][82][83][84][85][86][87][88][89][90].…”

Suzuki reaction: mechanistic multiplicity versus exclusive homogeneous or exclusive heterogeneous catalysis

“…For instance, Pd leaching under aryl halide action found earlier for the Heck reaction should theoretically (based on scheme 3) occur in the Suzuki reaction. Numerous confirmations of this were, indeed, found, 4,7,10,31,32 moreover the correlation between the activity and the amount of However, from the previous discussion of the Heck chemistry, it can be concluded that distinguishing between true homogeneous catalysis from heterogeneous catalysis in the Suzuki reaction is undoubtedly a very complicated task. Unfortunately, the results of the conventional tests on reaction homogeneity-heterogeneity 33 are ambiguous due to the interconversions of different catalyst forms (Scheme 3).…”

“…[4][5][6][7][8][15][16][17][18] The principle of most tests is the withdrawal of one of the catalyst forms from the reaction by any chemical or physical manipulation followed by measurement of the catalytic activity. But the most difficult situation might appear when catalyst forms (for instance dissolved and solid) are able to interconvert directly during the catalytic reaction.…”

“…Now it is quite clear that there is no consensus on the nature of the catalysis of this reaction (see review 2 published in 2006 and references cited therein). Analysis of the literature for the last two years indicates that some researchers advance the hypothesis of a homogeneous catalysis mechanism [3][4][5][6][7][8][9][10][11] while the others suggest a heterogeneous mechanism. [12][13][14][15][16][17][18] It is worth mentioning that the most convincing evidence is for the homogeneous mechanism of the Suzuki reaction.…”

Reactivity of the 2-aryl-6,8-dibromo-2,3-dihydroquinolin-4(1$H)$-ones in a palladium catalyzed Sonogashira cross-coupling reaction

“…15,16 The re-adsorption onto the solid support presumably immobilizes Pd and makes it unavailable to promote further cross-coupling with the excess terminal alkyne. To test the above assumption, we decided to employ a homogeneous Pd(0) source in the presence and absence of activated carbon.…”