title: N-Heterocyclic Olefin-Carbon Dioxide and -Sulfur Dioxide Adducts: Structures and Interesting Reactivity Patterns.
abstract: Depending on the amount of methanol present in solution, CO2adducts of N-heterocyclic carbenes (NHCs) and N-heterocyclic olefins (NHOs) have been found to be in fully reversible equilibrium with the corresponding methyl carbonate salts [EMIm][OCO2Me] and [EMMIm][OCO2Me]. The reactivity pattern of representative 1-ethyl-3-methyl-NHO-CO2adduct 4 has been investigated and compared with the corresponding NHC-CO2zwitterion: The protonation of 4 with HX led to the imidazolium salts [NHO-CO2H][X], which underwent decarboxylation to [EMMIm][X] in the presence of nucleophilic catalysts. NHO-CO2zwitterion 4 can act as an efficient carboxylating agent towards CH acids such as acetonitrile. The [EMMIm] cyanoacetate and [EMMIm]2cyanomalonate salts formed exemplify the first C-C bond-forming carboxylation reactions with NHO-activated CO2. The reaction of the free NHO with dimethyl carbonate selectively led to methoxycarbonylated NHO, which is a perfect precursor for the synthesis of functionalized ILs [NHO-CO2Me][X]. The first NHO-SO2adduct was synthesized and structurally characterized; it showed a similar reactivity pattern, which allowed the synthesis of imidazolium methyl sulfites upon reaction with methanol.
authors.affiliation: Fachbereich Chemie and Materials Science Centre, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, 35043, Marburg, Germany.
authors.forename: Lars H
authors.initials: LH
authors.lastname: Finger
authors.affiliation: Fachbereich Chemie and Materials Science Centre, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, 35043, Marburg, Germany.
authors.forename: Jannick
authors.initials: J
authors.lastname: Guschlbauer
authors.affiliation: Fachbereich Chemie and Materials Science Centre, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, 35043, Marburg, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Harms
authors.affiliation: Fachbereich Chemie and Materials Science Centre, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, 35043, Marburg, Germany. JSU@staff.uni-marburg.de.
authors.forename: Jörg
authors.initials: J
authors.lastname: Sundermeyer
keywords: carbenes; carbon dioxide fixation; carboxylation; heterocyclic olefins; ionic liquids