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N‐Heterocyclic Olefin–Carbon Dioxide and –Sulfur Dioxide Adducts: Structures and Interesting Reactivity Patterns
Author(s) -
Finger Lars H.,
Guschlbauer Jannick,
Harms Klaus,
Sundermeyer Jörg
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201602973
Subject(s) - chemistry , zwitterion , reactivity (psychology) , adduct , carboxylation , dimethyl carbonate , methanol , nucleophile , protonation , decarboxylation , medicinal chemistry , catalysis , isobutane , carbon dioxide , sulfone , organic chemistry , polymer chemistry , molecule , medicine , ion , alternative medicine , pathology
Depending on the amount of methanol present in solution, CO 2 adducts 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][OCO 2 Me] and [EMMIm][OCO 2 Me]. The reactivity pattern of representative 1‐ethyl‐3‐methyl‐NHO–CO 2 adduct 4 has been investigated and compared with the corresponding NHC–CO 2 zwitterion: The protonation of 4 with HX led to the imidazolium salts [NHO–CO 2 H][X], which underwent decarboxylation to [EMMIm][X] in the presence of nucleophilic catalysts. NHO–CO 2 zwitterion 4 can act as an efficient carboxylating agent towards CH acids such as acetonitrile. The [EMMIm] cyanoacetate and [EMMIm] 2 cyanomalonate salts formed exemplify the first C−C bond‐forming carboxylation reactions with NHO‐activated CO 2 . 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–CO 2 Me][X]. The first NHO‐SO 2 adduct was synthesized and structurally characterized; it showed a similar reactivity pattern, which allowed the synthesis of imidazolium methyl sulfites upon reaction with methanol.