Palladium-carbon heterogeneity, Heck reactions

Eisenstadt, A. Utilization of the heterogeneous palladium-on-carbon catalyzed Heck reaction in applied synthesis. Chem. Ind. 1998, 75,... 

Eisenstadt, A., Utilization of the Heterogeneous Palladium-on-Carbon Catalyzed Heck Reaction in Applied Synthesis. 17th ORCS, March 29-April 2, 1998, New Orleans. Eisenstadt, A., and Y. Keren, Process for the preparation of OMC , Israel Pat. 97850 (1991), EP 509426 (1992), USP 5 187 30 (1993). 

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. 

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). 

Gedanken et al. prepared palladium nanoparticles by decomposition of [Pd2(dba)3] or [Pd(OAc)2]/Me3(Cj4H29)NBr by extended exposure to ultrasound. In the case of [Pd2(dba)3], the colloidal metal particles were stabilized by amorphous carbon formed from dba. Activities of the soluble colloids in the Heck reaction were comparable to those of the heterogeneous catalyst palladium on charcoal (Table 2) [30, 31]. 

Another method that is widely used for C-C bond formation is the Heck coupling [3]. The arylation of olefinic double bonds is mostly catalyzed by palladium complexes in homogeneous solution. Important advantages of this reaction are the broad availability of arylbromides and chlorides and the tolerance of the reaction for a wide variety of functional groups. There were also developed heterogeneous Pd/C catalysts which exhibit high activity for the Heck reaction of aryl halides with olefins. The reaction conditions are 80 200 °C, solvents (NMP, DMF, tolueneAvater), base addition is necessary (NaOAc, amines, alkali carbonates). The reaction scheme can be described as follows (Eq. 8-22). 

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