Di(2-pyridyl)methylamine–palladium dichloride complex covalently anchored to a styrene-maleic anhydride co-polymer as recoverable catalyst for C–C cross-coupling reactions in water

Hybrid Organic‐Inorganic Materials from Di‐(2‐pyridyl)methylamine‐Palladium Dichloride Complex as Recoverable Catalysts for Suzuki, Heck and Sonogashira Reactions

“…When conditions C were adopted with catalyst 7a for the reaction of phenylboronic acid (8) with chlorobenzene (11b) to yield 12b, a modest conversion of 36% (GLC) was obtained after 6 h. Heating at higher temperature (150 8C) with the same base and solvent system did not improve very much the result (42% conversion after 6 h). However, our results are even better than those previously reported, [16] where the recycling was performed with an activated aryl chloride, p-chloroacetophenone, at higher temperature (130 8C) and higher amount of Pd (4.4%) in H 2 O and K 2 CO 3 as base, with decreasing activities of the recovered catalyst, as only modest yields were obtained from the second run even on increasing the reaction times from 3 to 14 h.…”

“…Palladium nanoparticles observed by TEM in supported bipyridyl complexes have also been described by Nµjera. [16] The amounts of Pd determined by ICP-MS in the product 10 isolated from the first cycle performed with catalyst 7a under conditions C and in the solid mixture obtained in this cycle by evaporation of the filtrate were found to be 12 and 80 ppm, respectively. Some authors have pointed out [20] that released Pd under reaction conditions acts as the true catalyst in immobilized palladium systems and redeposition of the metal after completion of the reaction is claimed.…”

“…sayed under the same conditions C with the material 7bSi, obtained by refluxing 7b with excess of bis(trimethylsilyl)amine for capping surface silanol groups, but the reaction was slower, four hours being required to afford a 97% isolated yield of 10. Nµjera [16] has used water or methanol-water as solvent systems in their recycling experiments with the di-(2-pyridyl)methylamine complex anchored to organic polymer, increasing reaction times being described for successive cycles. In our case, the use of a lower amount of water, dimethylformamide instead of methanol and potassium carbonate as base instead of KOH improved the recyclability (conditions C are better than conditions A).…”

“…Nµjera [16] used water as solvent at 100 8C in the presence of diisopropylamine as base and added TBAB for Heck recycling with the organic polymeric version of the palladium catalyst and increasing reaction times were required in successive cycles for full conversion (6 h in first cycle, 22 h from the second cycle). With our silica-anchored palladium complex Table 4.…”

“…The same group has covalently anchored this type of complexes 2 to a styrene-maleic anhydride copolymer providing a recyclable catalyst for those reactions. [16] Prompted by the publication of this report we have presented our preliminary results on the preparation of hybrid silica materials from the silylated monomer 2a ( Figure 1) and their activity and recyclability in Suzuki cross-couplings. [17] We describe here the full details of our work and its extension to Heck and Sonogashira reactions.…”