Polymer‐ and Ionic Liquid‐Containing Palladium: Recoverable Soluble Cross‐Coupling Catalysts

Abstract

Phosphine, palladacycle, and N‐heterocyclic carbene palladium complexes are highly active homogeneous catalysts that can promote a wide range of CC and CN cross‐coupling reactions. An evolution from homogeneous catalysis has been to anchor these complexes in a platform in such a way that the catalytic reaction still occurs in homogeneous phase, but the palladium complex can be recovered at the end of the reaction and reused to promote consecutive reactions. In the present review we describe those strategies to develop palladium complexes anchored to soluble polymers and ionic liquids showing the advantages and limitations of this approach to develop recyclable palladium catalysts.

Covalently Modified Graphenes in Catalysis, Electrocatalysis and Photoresponsive Materials

“…Particularly, metal complexes often decompose giving metal nanoparticles and it could be that these metal nanoparticles supported on insoluble supports also behave as highly active catalyst and, therefore, an alternative catalyst based on supported metal nanoparticles could be a more convenient option to the use of metal complexes . In principle, the order of catalytic activity commonly found is metal complex > small metal cluster > metal cluster > metal nanoparticle, thus, justifying the use of anchored complexes, but this assumption should not be taken for granted and careful checking of productivity and stability of the complex prior to anchoring is always necessary …”

“…Palladium catalysis has been led by the development of extremely active complexes that are based on the use of expensive ligands, such as biaryl phosphanes and NHC . Palladium‐catalyzed reactions have become among the most important toolbox reactions in organic synthesis due to the wide array of efficient C−C and C−heteroatom cross‐coupling reactions.…”

“…The main origin of this decomposition is the stress on the coordination bonds caused by the oxidative addition–reductive elimination steps in the mechanism. Thus, the mechanism requires reduction of Pd II to Pd 0 and subsequent re‐oxidation of Pd 0 to Pd II with the accompanying changes in the coordination number and geometry of corresponding Pd complexes . In view of these comments and also considering that carbon materials and in particular ACs have been widely employed to support Pd complexes or NPs, Gs have also recently reported as scaffolds to anchor NHC‐(ionic liquid derivative)‐palladium complex .…”

“…[55,132] In principle, the order of catalytic activity commonly found is metal complex > small metal cluster > metal cluster > metal nanoparticle, thus, justifying the use of anchored complexes,b ut this assumption should not be taken for granted and careful checking of productivity and stability of the complex prior to anchoring is always necessary. [133]…”

“…Palladium catalysis has been led by the development of extremely active complexes that are based on the use of expensive ligands, such as biaryl phosphanes and NHC. [133,142] Palladium-catalyzed reactions have become among the most important toolboxr eactions in organic synthesis due to the wide array of efficient CÀCa nd CÀheteroatom cross-coupling reactions. Therefore, there has been ac ontinuousi nterest in developing strategies consistingi na nchoring these highly active and efficient palladiumc omplexes on insoluble solids and scaffolds that could allow their recovery andr euse.…”