Background of Heterogeneous Heck Coupling

The immobilized, colloidal palladium catalyst, Si02-(C3H6SH)nPd is reported to induce the Heck reaction [14a] between ethyl iodide and ethyl acrylate. XPS data showed the presence of Pd(Il) on the surface of the colloidal Pd particles, owing to air oxidation this explains the different behavior of this and the Pd/C catalyst. Addition of BujN.HI and iodine greatly reduced the induction period. The catalytic activity of propylene carbonate-stabilized palladium colloids in the Heck reaction has been investigated [14b]. 

Semmelhack demonstrated that the addition of alkali metal chloride salts can sometimes markedly increase the yields of coupling products in heterogeneous Pd-catalyzed reactions, especially when the olefin component contains an amide function [15]. It has been claimed that palladium-grafted mesoporous material (MCM-41), designated Pd-TMSll, is one of the most active heterogeneous catalysts for the Heck reaction and enables C-C formation with activated and non-activated aryl substrates [16a,b]. Nanoscale particles of palladium clusters prepared by the ultrasonic reduction of Pd(OAc)2 and NR4X in THF or methanol, were also active for C-C couplings [17]. 

Pd metal on supports such as AI2O3, MgO, Si02, and CaCOg, and Raney Pd, have been reported to be effective in the Heck arylation, including that promoted by use of microwaves [18a-c]. With MgO supports electron transfer from the surface of the support to that of the metal leads to anchoring of the metal to the 

Polycinnamamide has been synthesized by use of the Heck reaction catalyzed by a recyclable Pd-graphite catalyst [19a], Because the catalyst is easily separated from the reaction mixture, the Pd content of the polymer can be lower and the polymer is less colored polymerization is more selective than when homogeneous catalysis is used [19b]. 

Phosphinated cellulose-bound Pd complexes (P-OPPh2PdCl2) [20a] and the polymer catalyst, P-Ph-Phen-Pd (reduced) have been used in Heck coupling reactions [20b]. 

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