Ionic Ullmann reaction

Electroreductive Pd-Catalyzed Ullmann Reactions in Ionic Liquids... 

Duran Pachon, L., Elsevier, C.J. and Rothenberg, G. (2006) Electroreductive palladium-catalysed Ullmann reactions in ionic liquids scope and mechanism. Adv. Synth. Catal., 348, 1705. 

Lloyd-Williams, P., Giralt, E. Atropisomerism, biphenyls and the Suzuki coupling peptide antibiotics. Chem. Soc. Rev. 2001, 30,145-157. Dupont, J., de Souza, R. F., Suarez, P. A. Z. Ionic Liquid (Molten Salt) Phase Organometallic Catalysis. Chem. Rev. 2002, 102, 3667-3691. Hassan, J., Sevignon, M., Gozzi, C., Schulz, E., Lemaire, M. Aryl-Aryl Bond Formation One Century after the Discovery of the Ullmann Reaction. Chem. Rev. 2002, 102, 1359-1469. 

SCHEME 2. Ionic aromatic nucleophilic substitution mechanism for the Jourdan-Ullmann reaction. 

While all the hb polyethers mentioned above were the products of ionic nucleophilic substitutions, a couple of hb polyethers were prepared via the Ullmann reaction from the dibromophenols (a) and (b), Formula 11.10 [88, 89]. Quite analogous to inefficient syntheses of linear polyethers only low molar mass hb polyethers were isolated from those trifunctional monomers. 

Scheme 2.13 Ionic liquids used in the Ullmann reaction.

A further evidence on the acceleration enjoyed by a typical Pd-catalysed reaction, the Heck reaction, in an ionic phase ( V-mcthyl-Y.Y. V.-trioctylammonium chloride or Aliquat 336) is found in a triphasic protocol developed by Tundo and coworkers. 7b.The arylation of electron poor olefins is catalysed by palladium supported on charcoal (Pd/C) and is carried out in the heterogeneous isooctane/Aliquat 336/water system (Figure 27). Under this multiphasic condition, Aliquat 336 forms a third liquid phase between the organic and the aqueous phase that traps the catalyst. The use of phosphines is not necessary. As a matter of fact, Aliquat 336 incorporates the solid-supported catalyst and ensures an efficient mass transfer between the bulk phases resulting in an increase of the reaction rate of an order of magnitude compared to the reaction in the absence of the ionic liquid. A determing role is played by the base while I LN drives the reaction towards the formation of ethyl cinnamate, reaction carried out in the presence of KOH lead to formation of Ullmann dimerisation products. 

Yoshimiu-a and Iwasaki of Sumitomo Chemical Co. have synthesized aromatic ionomers containing pendant perfluorosulfonic acid groups (Fig. 7.29) [79]. Poly (arylene ether sulfone) was brominated and then perfluorosulfonated via Ullmann coupling reaction in the presence of copper catalyst. The lEC was controllable up to 1.58 meq/g. The obtained ionomer membranes behaved very differently from the typical sulfonated aromatic ionomer membranes. Characteristic hydrophobic/hydro-philic separation (ca. 3-4 nm) was observed in the smaU-angle X-ray scattering (SAXS) analyses of the hydrated samples. The ionic clusters were slightly smaller... 

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