Pd-catalyzed Heck arylation of cycloalkenes—studies on selectivity comparing homogeneous and heterogeneous catalysts

Efficient Heterogeneously Palladium‐Catalysed Heck Arylation of Acrolein Diethyl Acetal. Selective Synthesis of Cinnamaldehydes or 3‐Arylpropionic Esters

“…In previous studies, we demonstrated that the dehalogenation was mainly due to the formation of palladium particles or agglomerates in the reaction media, while the Heck arylation resulted from soluble molecular Pd species. [83] The results presented here suggest that, depending on the substrate, rapid Pd agglomeration could occur while using homogeneous ligand-free PdA C H T U N G T R E N N U N G (OAc) 2 , whereas the use of the [PdA C H T U N G T R E N N U N G (NH 3 ) 4 ]/NaY retards such agglomeration.…”

“…[42] This result contrasts with that obtained from ICP-AES analyses of the clear supernatant solutions while evaluating the recycling, attesting clearly that dissolution-redeposition equilibrium occurs during such coupling reactions, as has often been suggested in the literature. [73,[83][84][85] This equilibrium is therefore clearly dependent on the reaction temperature, and is strongly displaced toward the redeposition at low (ambient) temperatures.…”

Poly(4‐vinylpyridine) and Quadrapure TU as Selective Poisons for Soluble Catalytic Species in Palladium‐Catalyzed Coupling Reactions – Application to Leaching from Polymer‐Entrapped Palladium

“…Traditional heterogeneous precatalysts such as palladium on carbon (Pd/C) [1][2][3][4] or palladium on oxides [4][5][6] have been used effectively, although it has been conclusively shown in essentially all cases they operate by a release and capture mechanism, whereby soluble palladium that is the active catalyst is leached from the solid. [4][5][6][7][8] After all the aryl halide is consumed, the soluble palladium can in some cases redeposit on the support. Despite numerous reports claiming palladium surface-catalyzed Heck reactions, there is no conclusive proof in the literature to support them.…”

Designing Nanostructured Carbon Xerogels

“…Nevertheless, the disadvantages of heterogeneous catalysis are the presence of two different phases and the control of the active sites nature. On the other hand, regarding to homogeneous catalysis, although reactions take place in a single phase and catalysts can be tailored, their carriage in industrial processes is lower due to their sometimes limited stability and their difficult recovery (Choplin & Quignard, 1998;Djakovitch et al, 2004;Fontecha-Cámara et al, 2011). Most of published works on carbon gels used in catalysis field are focused on heterogeneous processes and the great interest of carbon gels in this field research is due to their attractive features such as: tailored pore texture, possibility of enriching their surface chemistry by different processes, high packing density, high durability under harsh conditions, etc.…”