Palladium on Calcium Carbonate Combined to 2‐Hydroxypropyl‐α/β‐cyclodextrins: A Selective Catalytic System for Aqueous Heck Coupling and Hydroarylation

Abstract

An efficient, selective and recoverable catalytic system for ligand-free aqueous Heck reactions using hydroxypropylated cyclodextrins (HPCDs) and palladium on calcium carbonate (Pd/CaCO 3 ) is highlighted. Remarkably, stereo-and chemoselectivities could be tuned by the cavity size of cyclodextrins, exploiting the relevance of host-guest interactions. UVVis experiments have led to strong evidence concerning an interplay between Pd(II) and a-HPCD, possibly ascribed to a reduction/stabilization effect of CDs. Unexpectedly, hydroarylation was the favored pathway with acrylonitrile which provided access to 3-phenylpropionitrile derivatives without usual hydride donors. Finally, determination of soluble PdA C H T U N G T R E N N U N G (0/II) via AAS enabled the definition of a predominant homogeneous mechanism in which TONs over 5000 were observed.

Aqueous Heck Arylation of Acrolein Derivatives: The Role of Cyclodextrin as Additive

“…These results indicated that the cyclodextrins could act as a protecting layer of the palladium particles and so allowed to keep moderate size. Such behavior has been previously observed in the case of metallic ruthenium nanoparticles [28,29] and in C-C cross-coupling reactions in aqueous media, including Heck, Suzuki and Sonogashira reactions, while using Pd nanoparticles stabilized by 2-hydroxypropyl-a-cyclodextrin [13]. Since cyclodextrins avoided sintering of palladium particles, together with an important concentration, the catalytic activity is higher compared to the reaction in the absence of cyclodextrins.…”

“…However, the exclusive use of water often leads to modest yields and the use of phase transfer agent additives like tetraalkylammonium salts are essential in order to circumvent such limitation [9,10]. Recently, the effect of cyclodextrins as phase-transfer agent on the C-C cross-coupling reaction in water was demonstrated [11][12][13][14][15][16]. Moreover, the beneficial effect of the presence of cyclodextrins on the selective preparation of cinnamaldehyde and aryl propionic ester using Pd salts in aqueous phase was reported [17].…”

β‐cyclodextrin‐capped palladium nanoparticle‐catalyzed ligand‐free Suzuki and Heck couplings in low‐melting β‐cyclodextrin/NMU mixtures

“…Indeed, CD derivatives have commonly been applied successfully in various organic reactions, especial involving green chemistry. Among these, CDs have attracted a wide interest in the synthesis and stabilization of transition metal nanoparticles for carbon–carbon bond formation . Furthermore, Matt et al showed that cavity‐shaped ligands could bring an added value to the efficiency of Suzuki–Miyaura coupling .…”

Chemically Modified Cyclodextrins: An Attractive Class of Supramolecular Hosts for the Development of Aqueous Biphasic Catalytic Processes

“…It was assumed that hydroxylpropylated CD increased the dispersion of the Pd/BaCO 3 and stabilized Pd clusters leached from the support. In fact, the heterogeneous Pd/BaCO 3 solid could act as a reservoir of catalytically active Pd species [109,110].…”