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Medientyp: E-Artikel Titel: Carbon Dioxide Fixation by Lithium Amides: DFT Studies on the Reaction Mechanism of the Formation of Lithium Carbamates Beteiligte: Lill, Sten O. Nilsson; Köhn, Uwe; Anders, Ernst Erschienen: Wiley, 2004 Erschienen in: European Journal of Organic Chemistry, 2004 (2004) 13, Seite 2868-2880 Sprache: Englisch DOI: 10.1002/ejoc.200400163 ISSN: 1434-193X; 1099-0690 Entstehung: Anmerkungen: Beschreibung: AbstractA realistic picture of the complete insertion reaction for a representative example of the formation of carbamates from lithium amides is given by combining experimental information with detailed DFT investigations. The chiral lithium (S)‐2‐(pyrrolidin‐1‐ylmethyl)pyrrolidide (2) reacts with CO2 to form its corresponding carbamate. In this reaction the second pyrrolidine ring functions as an intramolecular ligand, and therefore, “symmetrical” as well as “unsymmetrical” dimers of 2 have to be taken into account. On the energetically preferred reaction pathway this amide exists predominantly as a (solvated) dimer 4. Attack by CO2 occurs in an “end‐on” manner to give several heterodimers 5 which are composed of a lithium amide and a lithium carbamate. This exergonic step is rate determining, and the activation barrier was estimated to be about 10 kcal mol−1. A second lithium‐mediated CO2 insertion into a nitrogen−lithium bond yields the encounter complex 5d−(CO2), which then goes on to form several almost isoenergetic homodimeric carbamates 6. This strongly exergonic insertion reaction has a barrier of 9.7 kcal mol−1. We also report on novel lithium‐mediated CO2 insertion reactions into oxygen−lithium bonds in lithium carbamates. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)