A New Class of Organosuperbases, N-Alkyl- and N-Aryl-1,3-dialkyl-4,5-dimethylimidazol-2-ylidene Amines: Synthesis, Structure, pKBH+Measurements, and Properties

0389335 - ÚOCHB 2013 RIV DE eng J - Journal Article
Kunetskiy, Roman Alexejevič - Polyakova, Svetlana - Vavřík, Jiří - Císařová, I. - Saame, J. - Nerut, E. R. - Koppel, I. - Koppel, I. A. - Kütt, A. - Leito, I. - Lyapkalo, Ilya
A New Class of Organosuperbases, N-Alkyl- and N-Aryl-1,3-dialkyl-4,5-dimethylimidazol-2-ylidene Amines: Synthesis, Structure, pKBH+Measurements, and Properties.
Chemistry - A European Journal. Roč. 18, č. 12 (2012), s. 3621-3630. ISSN 0947-6539. E-ISSN 1521-3765
Institutional research plan: CEZ:AV0Z40550506
Keywords : amines * aromaticity * basicity * imidazolylidene amines * steric hindrance * substituent effects * superbases
Subject RIV: CC - Organic Chemistry
Impact factor: 5.831, year: 2012

A series of stable organosuperbases, N-alkyl- and N-aryl-1,3-dialkyl-4,5-dimethylimidazol-2-ylidene amines, were efficiently synthesized from N,N’-dialkylthioureas and 3-hydroxy-2-butanone and their basicities were measured in acetonitrile. The derivatives with tert-alkyl groups on the imino nitrogen were found to be more basic than the tBuP1(pyrr) phosphazene base in acetonitrile. The origin of the high basicity of these compounds is discussed. In acetonitrile and in the gas phase, the basicity of the alkylimino derivatives depends on the size of the substituent at the imino group, which influences the degree of aromatization of the imidazole ring, as measured by 13C NMR chemical shifts or by the calculated DNICS(1) aromaticity parameters, as well as on solvation effects. If a wider range of imino-substituents, including electron-acceptor substituents, is treated in the analysis then the influence of aromatization is less predominant and the gas-phase basicity becomes more dependent on the field-inductive effect, polarizability, and resonance effects of the substituent.
Permanent Link: http://hdl.handle.net/11104/0218226