0000000000350757
AUTHOR
Immacolata Tommasi
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.
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.
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…