Book Review: Applied Homogeneous Catalysis with Organometallic Compounds. Vols. 1–3. 2nd. Edition. Edited by Boy Cornils and Wolfgang A. Herrmann

Synthesis of chemisorbed imidazolium and phosphonium cations by reaction of ionic liquid precursors with silica.

The reaction of four different basic ionic liquid precursors with Aerosil®300 is presented. Chemisorbed imidazolium and phosphonium cations, with silanolate anions as part of the silicatic support, were obtained and investigated with various solid state NMR techniques.

Straightforward Synthesis of Donor‐Stabilised Phosphenium Adducts from Imidazolium‐2‐carboxylate and Their Electronic Properties (Eur. J. Inorg. Chem. 31/2007)

The cover picture shows one of donor-stabilized phosphenium compounds which have been obtained by direct addition of chlorophosphanes to the 1,3-dimethylimidazolium-2-carboxylate without any further purification step. Their stronger κ-acceptor character similar to phosphites and their ionic nature render these ligands very promising in the development of new continuous-flow catalytic processes. Details of phosphorylation mechanisms of imidazolium-2-carboxylate as well as the electronic and steric properties of these adducts are discussed in the article by J. Andrieu et al. on p. 4877 ff.

Ionic Liquids: Media for Better Molecular Catalysis

Ionic liquids (ILs) are more and more suggested as substitutes for traditional solvents in organic synthesis and catalysis. They are suitable candidates for the dissolution of ionic complexes. They can activate and retain them in a polar state: in fact, they act as sequestrands, opening the route to two-phase processes and easier catalyst recovery. This paper reviews authors' results with the development of new syntheses of ILs and applications in carbon–carbon bond formation (dimerisation of methyl acrylate) and redistribution (ring closing metathesis) reactions using ionic precatalysts.

Buchbesprechung: Applied Homogeneous Catalysis with Organometallic Compounds. 2. Ausgabe. Herausgegeben von Boy Cornils und Wolfgang A. Herrmann

1,3-Dimethylimidazolium-2-carboxylate: the unexpected synthesis of an ionic liquid precursor and carbene-CO2 adductElectronic supplementary information (ESI) available: experimental data for 1,3-dimethylimidazolium-2-carboxylate. Supplemental crystal structure data. ORTEP, hydrogen bonding and packing diagrams. See http://www.rsc.org./suppdata/cc/b2/b211519k/

1,3-Dimethylimidazolium-2-carboxylate is formed in good yield, rather than the anticipated organic salt, 1,3-dimethylimidazolium methyl carbonate, as the reaction product resulting from both N-alkylation and C-carboxylation of 1-methylimidazole with dimethyl carbonate; the crystal structure of the zwitterion exhibits π-stacked rings and two-dimensional sheets constructed by hydrogen-bonds from imidazolium-ring hydrogens to the carboxylate group.

Biphasic dimerisation of methylacrylate--immobilisation and stabilisation of cationic Pd-catalysts in ionic liquids by an ammoniumphosphine ligand.

The first continuous, biphasic, Pd-catalysed dimerisation of methylacrylate is described. The biphasic system has been realised by using a tetrafluoroborate ionic liquid as catalyst medium and an ammoniumphosphine ligand to immobilise and stabilise the Pd-catalyst.

Mono- and Bidentate Phosphine Ligands in the Palladium-Catalyzed Methyl Acrylate Dimerization

The influence of several phosphine ligands on the activity, selectivity and stability of the catalytic system Pd(acac)2, ligand, [HOEt2][BF4] was studied in the dimerization of methyl acrylate (MA). It was found that the catalyst's activity increased with increasing the basicity of the monodentate ligands used, whereas bulky phosphines lowered the linearity of the dimers and the reaction rates. With chelating P N-, P P-, and P As-ligands the Pd-catalyst could be efficiently stabilized during the reaction. The use of 1-dibutylphosphino-2-dimethylaminoethane as ammonium tetrafluoroborate salt allowed the highest overall activity.

Straightforward synthesis of donor-stabilised phosphenium adducts from imidazolium-2-carboxylate and their electronic properties

Cationic imidazolium-2-phosphanes were obtained by the addition of a chlorophosphane (R2PCl, R = Ph, iPr or Cy) to 1,3-dimethylimidazolium-2-carboxylate without the need for a purification step. An additional anion exchange reaction with KPF6 led to the corresponding halide-free ligands in excellent yields. The molecular structure of one of them was examined both in the solid state and in solution. The lone pair of electrons on the phosphorus atom is not delocalised to the imidazolium fragment and thus remains available for further metal coordination. As such compounds can be described as phosphenium cations stabilised by a N-heterocarbene donor base, the electronic properties of the Lewis …

Selective palladium-catalysed dimerisation of methyl acrylate in ionic liquids: towards a continuous processThis work was presented at the Green Solvents for Catalysis Meeting, held in Bruchsal, Germany, 13–16th October 2002.

The activity and stability of cationic palladium complexes [Pd(PBu3)2S2]2+ used for the selective tail-to-tail dimerisation of methyl acrylate are significantly improved with the utilisation of ionic liquids like [BMIM][BF4] or the protonated N-butyl-imidazole, [HBIM][BF4]. Problems related to product inhibition and catalyst recycling are overcome by running the reaction in a two-phase mode, toluene being used as extractant. Catalyst stabilisation is further improved by trapping the ancillary ligand into the ionic liquid with an ionic tail: with the use of 1-dibutylphosphino-2-dimethylaminoethane, the catalyst is stable for more than 100 h, therefore demonstrating the feasibility of a conti…