Heck Reactions of Non-activated Aryl Bromides

1 Heck Reactions of Non-activated Aryl Bromides (Table 10.1) 

Investigations of a variety of zeoHtes by Djakovitch et al. showed that the shuc-ture or the Si/Al ratio had little influence on the activity of the catalyst. All catalysts achieved complete conversions of bromobenzenes in 20 h with 0.2 mol% Pd at 140 °C [147]. However, kinetic experiments showed that monomeric Pd complexes (in particular [Pd(NH3)4] ) incorporated into the zeolite cages have reaction rates orders of magnitude higher than Pd particles. The immobilized complex converts the aryl halides within a few minutes. Recycling experiments showed that the 

A new type of support was recently presented by the group of Kaneda. In their work they described the controlled synthesis of hydroxyapatite-supported Pd complexes and their application in Heck reactions of bromobenzene with styrene and butyl acrylate [150], In both cases high TON (up to 47000) were achieved using low catalyst concentrations (2 x 10 mol%) and moderate temperatures (120 °C) within 24 h. 

Metal oxides. Beside mesoporous silica materials conventional metal oxides have been applied for the synthesis of solid Pd catalysts for C—C coupling reactions. Alper and coworkers [151] and Singh and coworkers [144] immobilized Pd complexes on a modified silica surface modified by covalent anchoring. The resulting solid catalyst was tested in reactions of several non- and deactivated aryl bromides (bromobenzene, p-bromotoluene, p-bromoanisole) and butyl acrylate or styrene. Only TONs around 100 were achieved after 1 day reaction. 

Entry Catalyst Cat. Cone. [mol%] Alkene Solvent Base T [°q t[h] Yield [%1 Ref. 

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