Carbonylation Reactions of Iodoarenes with PAMAM Dendrimer-Palladium Catalysts Immobilized on Silica

Abstract

Palladium complexes immobilized onto generation 0-3 PAMAM dendrimers supported on silica were used as catalysts for the carbonylation of iodobenzene in methanol to form methyl benzoate. High yields were obtained and the catalyst was recycled 4-5 times without significant loss of activity. The carbonylation reaction was found to be applicable to a variety of iodoarenes regardless of the nature of the substituent. IntroductionThe carbonylation of haloarenes has been extensively investigated in the liquid phase.1 Most of the work reported in this area has involved bromo-and iodoarenes as starting materials, and metal complexes as catalysts which are capable of oxidative addition to a C-X bond (e.g. Pd or Rh). Phosphine-modified palladium complexes such as dichlorobis(triphenylphosphine)palladium(II) or bromoarylbis(triphenylphosphine)palladium(II) are catalytically active for the carbonylation of iodobenzene or bromobenzene to produce benzoic acid derivatives.2 The carbonylation of haloarenes with Pd catalysts and phase transfer systems, (e.g., poly(ethylene glycol) and watersoluble catalysts 3 ) gave satisfactory yields of benzoic acids. The carbonylation reaction can proceed in a different manner if the intermediate is intercepted by another species. An example is the novel approach for the one-pot preparation of R-amino amides by Pdcatalyzed double carbohydroamination of haloarenes. 4 The preparation of polyesters and polyamides by palladium-catalyzed alkoxycarbonylation of haloarenes 5 is also noteworthy. Different strategies have been successfully pursued to overcome the low reactivity of chloroarenes toward oxidative addition. Milstein et al. 6 described the use of Pd complexes containing electron-rich and bulky chelating diphosphines. Also, Osborn et al. 7 and Alper and Grushin 8 demonstrated that Pd complexes with phosphines possessing both high basicity (pK a > 6.5) and substantial steric hindrance are useful catalysts (e.g. (Cy 3 P) 2 PdCl 2 ) for the carbonylation of chlorobenzene under mild conditions. Other methods of functionalizing chloroaromatics include photochemical activation 9 or the use of tricarbonyl(chloroarene)chromium complexes which react in a stoichiometric fashion. 10Heterogeneous catalysts have advantages of heat stability and ease of separation from the product when compared with homogeneous catalysts. Application of solid catalysts for the carbonylation of haloarenes has been examined by the use of NiCl 2 on pumice 11 or on SiO 2 . 12 A study on the use of solid catalysts for the carbonylation of haloarenes concluded that Pd supported on charcoal was the most active system. 13Transition metal catalysis based on functionalized dendrimers has become an interesting and promising way of using a heterogeneous catalytic system. From a catalytic point of view the ideal catalyst should be highly active and selective under mild conditions, stable and easy to separate from the product by using a simple process such as filtration. 14 Dendrimer metal catalysts can, in principle, fill the gap...

Silica-Supported Dendrimer-Palladium Complex-Catalyzed Selective Hydrogenation of Dienes to Monoolefins

“…For example, dendrimer-rhodium complexes on silica or a resin, display excellent activity and recyclability for the hydroformylation of alkenes. [1 -3] Dendrimer-palladium complexes have been used to catalyze the Heck coupling reaction of bromoarenes, [4] the carbonylation of haloarenes, [5] as well as the hydroesterification, [6] and oxidation [7] of alkenes. It was anticipated that, under appropriate conditions, the dendritic Pd complexes could effect selective reduction reactions.…”

Dendrons and dendritic catalysts immobilized on solid support: Synthesis and dendritic effects in catalysis

“…The formed structures were extensively studied and tested as heterogeneous catalysts in the iodoarene carbonylation reaction (Scheme 21). 63 Quantitative complexation was observed with zero-generation-to-second-generation-derived ligands for the PdCl 2 fragment. However, for higher generations and with bulkier Pd fragments, only partial functionalization was achieved.…”

“…In our experiments on polystyrene-polyether dendron supports, the lower crosslinking upon the complexation of monodentate phosphines to Co bimetallic and Pd monometallic sites was observed with both the naked eye and NMR (a narrowing of signals in gel-phase 31 P NMR). 54,63 …”

Recyclable Tridentate Stable Palladium(II) PCP‐Type Catalysts Supported on Silica for the Selective Synthesis of Lactones

“…[10] Immobilization of the homogeneous catalyst by means of a heterogeneous support can, in principle, retain the properties observed for the homogeneous system and allow simple separation from the reaction mixture. It is known that palladium complexes with pincer ligands (e.g., PCP, this ligand comprises an anionic aryl ring which is ortho, ortho-disubstituted with CH 2 PR 2 .…”