A Highly Active Water‐Soluble Cross‐Coupling Catalyst Based on Dendritic Polyglycerol N‐Heterocyclic Carbene Palladium Complexes

Abstract

A new water-soluble polyglycerol derivative functionalized with N-heterocyclic carbene palladium complexes was prepared and applied as catalyst for Suzuki cross-coupling reactions in water. The complex displays a metal loading of around 65 metal centers per dendrimeric molecule, which is estimated to contain 130 chelating groups and thus corresponds approximately to the formation of 2:1 NHC/metal complexes. Monomeric analogues were also synthesized to validate the reactivity of the dendritic catalyst. Both types of catalysts were tested with various aryl bromides and arylboronic acids. Turnover frequencies of up to 2586 h(-1) at 80 degrees C were observed with the dendritic catalyst along with turnover numbers of up to 59 000, which are among the highest turnover numbers reported for polymer-supported catalysts in neat water. The dendritic catalyst could be used (reused) in five consecutive reactions without loss in activity.

Synthesis and Application of Water‐Soluble NHC Transition‐Metal Complexes

“…Meise et al. also incorporated a macrocycle in their ligand design and isolated poly(ethylene glycol) bound Pd compounds, such as C54 68b. Finally, Byun et al.…”

An efficient Pd–NHC catalyst system in situ generated from Na2PdCl4 and PEG-functionalized imidazolium salts for Mizoroki–Heck reactions in water

“…Since the pioneering report of a sulfonate-functionalized NHC ligand by Shaughnessy [40], a number of water-soluble NHC ligands, functionalized with sulfonate- [41–46], carboxylate- [47–52], polyether- [53–59] and other hydrophilic groups [60–63], have been developed and used in the aqueous Pd-catalyzed cross-coupling reactions. Among them, most of them were contributed to Suzuki–Miyaura reactions and only a very few examples were reported for Mizoroki–Heck reactions [45,51,53,57].…”

Polyisobutylene-supported N-heterocyclic carbene palladium catalysts

“…These examples mostly used insoluble cross-linked polymers [17aeg] and nanoparticles [17h,17i]. Studies using soluble polymers have largely been restricted to the use of polar polymers like poly(ethylene glycol) [18].…”