Heck Reactions of Iodobenzene and Methyl Acrylate with Conventional Supported Palladium Catalysts in the Presence of Organic and/or Inorganic Bases without Ligands

Abstract

The vinylation of iodobenzene with methyl acrylate has been studied with several supported palladium catalysts in N-methylpyrrolidone in the presence of triethylamine and/or sodium carbonate. The reaction can be performed in air without any solubilizing or activating ligands. It was found that significant amounts of palladium leach out into the solvent and these dissolved Pd species essentially catalyze the reaction. It is interesting, however, that almost all the palladium species in the solution can redeposit onto the surface of the supports after the reaction has been completed (at 100% conversion of iodobenzene). Thus, the catalysts were recyclable without loss of activity. The use of both inorganic and organic bases is very effective in the promotion of the palladium redeposition as well as in the enhancement of the reaction rate. For Heck reactions with bromobenzene and chlorobenzene it was found that the use of triethylamine and sodium carbonate increases the selectivity of the Heck coupling product (benzene is also produced for these two substrates), but the mixed bases do not affect the overall rate of reaction as much.

Synthesis of glycerol carbonate from glycerol and urea using zinc-containing solid catalysts: A homogeneous reaction

“…The precipitation/re-deposition of active species at the later stage of reaction is phenomenally similar to the results of Heck coupling reactions with conventional supported Pd catalysts. The supported metal is leaching to the organic liquid phase and the reaction is homogeneously catalyzed by the dissolved Pd species; at close 100 % conversion, however, those Pd species will return onto the surface of the parent supported catalysts [34,35].…”

Metallic Palladium in the Heck Reaction: Active Catalyst or Convenient Precursor?

“…[10,15] Indeed, a significant palladium leaching into the solution after just one catalytic cycle was often observed. [12,13] In this communication, we wish to report that: (i) under Heck conditions heterogeneous palladium metal catalysts undergo significant metal leaching, caused primarily by the presence of aryl halides (bromides and even chlorides); (ii) the presence of a coordinating base such as sodium acetate promotes metal leaching with relatively less reactive aryl halides; (iii) the released soluble metal species are active catalysts for the Heck reaction.…”

The Heck reaction in the production of fine chemicals

“…In addition, reactivity is usually severely compromised. Immobilization of ligandless palladium has some merit (57). Even though leaching occurs extensively, the palladium precipitates on the support at the end of the reaction.…”