Heterogeneous Heck reaction

Most recently, the test has been applied to examination of the mechanism of a heterogeneous Heck reaction, promoted by Pd on alumina [25]. In the presence of the solid catalyst, 4-iodobenzamide coupled efficiently with butyl acrylate yielding the cinnamate, and it was suspected that the catalytic agent was a soluble form of palladium released from and then recaptured by the alumina support. To test this, the amide was attached to a commercially available resin with suitable functionality, and the supported amide (15 in Scheme 9.10) was allowed to react with the acrylate and Pd on alumina. The same product, identified after release from the polymer by TFA treatment, was formed, and further experiments were able to narrow down the form of the soluble catalysing palladium species. 

Scheme 9.10 Application of a three-phase test to investigate the nature of the catalyst in a heterogeneous Heck reaction.

It has been suggested that active sites in heterogeneous Heck reactions are actually dissolved palladium species.1901 Such a hypothesis is in agreement with a mechanism where palladium nanoparticles suspended in an ionic liquid are suggested to act as reservoir to a molecular catalyst, which is formed upon oxidative addition, as shown in Figure 6.4.1311... 

Hagiwara, H., Shimizu, Y, Hoshi, T. et al. (2001) Heterogeneous Heck reaction catalyzed by Pd/C in ionic liquid. Tetrahedron Lett., 42, 4349-51. 

Zhao, F., Shirai, M. and Arai, M. (2000) Palladium-catalyzed homogeneous and heterogeneous Heck reactions in NMP and water-mixed solvents using organic, inorganic and mixed bases. J. Mol. Catal. A Chem., 154, 39-44. 

The formation of C-C bonds is a fundamental process in organic chemistry. There are many catalytic systems that can achieve this transformation under mild conditions, and it is therefore not surprising that supported versions of these catalysts have received significant attention. Ikegami and coworkers have prepared an assembled catalyst of palladium and a non-cross-linked amphiphilic polymer ligand to perform the heterogeneous Heck reaction of a series of aryl iodides with acrylates, styrenes, and acrylic acids (Scheme 4). An efficient reaction was... 

The much more stable MIL-lOO(Cr) lattice can also be impregnated with Pd(acac)2 via incipient wetness impregnation the loaded catalyst is active for the hydrogenation of styrene and the hydrogenation of acetylene and acetylene-ethene mixtures to ethane [58]. MIL-lOl(Cr) has been loaded with Pd using a complex multistep procedure involving an addition of ethylene diamine on the open Cr sites of the framework. The Pd-loaded MIL-lOl(Cr) is an active heterogeneous Heck catalyst for the reaction of acrylic acid with iodobenzene [73]. 

Studies on heterogeneous Pd metal catalysts for the arylation of alkenes with aryl halides (the Mirozoki-Heck reaction often reported as Heck reaction) [28] continue to... 

To assess the utility of this resin, we chose to employ it in the evaluation of the heterogeneity of a commercial polymer-entrapped Pd(OAc)2 precatalyst, Pd-EnCat, also sold by Reaxa. This precatalyst was designed with the goal of providing a heterogeneous catalyst that would allow simple removal of palladium from reactions (24-26). PVPy and QTU were first used as poisons in the Heck reaction of iodobenzene and n-butyl acrylate in DMF using PdfC as the palladium... 

The scope of the multiphasic system was extended to coupling reactions—like the Heck reaction—using a heterogeneous supported catalyst, such as Pd/C. The rationale here lay in the observation that aryl halides were activated in the multiphasic system (as seen for hydrodehalogenation), and that therefore they should also be activated toward C-C coupling reactions. 

Wang HG, Zheng XM, Ping C, Zheng XM. The fabrication of reactive hollow polysiloxane capsules and their application as a recyclable heterogeneous catalyst for the Heck reaction. J Mater Chem 2006 16 4701-4705. 

Wall, V.M., Eisenstadt, A., Ager, D.J. and Laneman, S.A. (1999) The Heck reaction and cinnamic add synthesis by heterogeneous catalysis palladium on carbon catalyst gives improved production. Platinum Met. Rev., 43, 138. 

Mukhopadhyay, S., Rothenberg, G., (oshi, A., Baidossi, M. and Sasson, Y. (2002) Heterogeneous palladium-catalyzed Heck reaction of aryl chlorides and styrene in water under mild conditions. Adv. Synth. Gated., 344, 348. 

For such a modular configuration, it is claimed that a large number of heterogeneously catalyzed reactions can be performed, e.g. Heck and Suzuki coupling, acid-catalyzed esterifications and reductions of functional groups [83], However, for the mentioned process, the catalyst and reactants are not named and no reaction conditions or experimental results, e.g. yield, selectivity or nature of side products, are given. 

Heck reactions of iodo- and bromoarenes and ethyl acrylate have been conducted under heterogeneous conditions with Pd/C in [C4mim][PF6].38 Bromobenzene achieved a 40% yield after 12 h at 140 °C. The significant advantage of this method is in product isolation and recovery of the... 

Palladium on activated carbon has turned out to be a highly versatile, simple heterogeneous catalyst for one-pot multistep syntheses. Recently, Djakovitch and coworkers [42] have demonstrated that low catalyst loadings of Pd on activated carbon efficiently catalyze the Heck reaction of bromo benzene and styrene giving rise to T-stilbene (1) (92%), Z-slilbcnc (1%), and 1,1-diphenylethene (7%). If the Heck products are not isolated but an atmosphere of 20 bar of hydrogen is imposed onto the reaction vessel the sequence furnishes 1,2-diphenylethane (2) in 93% yield (Scheme 1). 

Zhao F, Murakami K, Shirai M, Arai M (2000) Recyclable homogeneous/heterogeneous catalytic systems for heck reaction through reversible transfer of palladium species between solvent and support. J Catal 194 479... 

Although aryl and vinyl halides have found vast applications in Heck coupling, aromatic diazonium salts, particularly the isolable tetrafluoroborates, proved successful in the work of Kikukawa et al. [23 a, b] and a one-pot reaction with the C-C-coupling step [23 c-e]. Extensions of this tandem diazotation Heck reaction technique were reported by Beller et al. (eq. (5)) [23 f], including heterogeneous Pd/carbon catalysts [23 g]. 

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