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Are Polar Organometallic Compounds "Carbanions"? The Gegenion Effect on Structure and Energies of Alkali-Metal Compounds

Lambert, Christoph ; von Ragué Schleyer, Paul

Angewandte Chemie (International ed.), 1994-06, Vol.33 (11), p.1129-1140 [Revista revisada por pares]

Zug: Hüthig & Wepf Verlag

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Título:
Are Polar Organometallic Compounds "Carbanions"? The Gegenion Effect on Structure and Energies of Alkali-Metal Compounds
Autor: Lambert, Christoph ; von Ragué Schleyer, Paul
Materias: Alkali and alkaline-earth metals derivatives ; Alkali metals ; Carbanions ; Chemistry ; Exact sciences and technology ; Ion pairs ; Organic chemistry ; Organometalloidal and organometallic compounds ; Preparations and properties
Es parte de: Angewandte Chemie (International ed.), 1994-06, Vol.33 (11), p.1129-1140
Notas: ArticleID:ANIE199411291
Dedicated to Professor Ernst Otto Fischer on the occasion of his 75th birthday
ark:/67375/WNG-7P0ZRWLF-Q
istex:DFAE24C7C4A454A6EF2DF83E0556859F57C32415
Descripción: Polar organometallic compounds such as alkyllithium compounds or Grignard reagents often are conceived as “carbanions”, although it is well known from experiments that the metal gegenions may have a strong, and often directing, influence on the reactivity (for example, the basicity vs. the nucleophilicity) of the “carbanion”. This demonstrates that “carbanions” are tightly associated ion pairs, at least in commonly used less polar or nonpolar solvent systems like ethers or hydrocarbons. However, despite about ninety years of widespread application of these organometallic compounds as bases or nucleophilic reagents, the role of the gegenion is not yet understood fully. The focus of this review is on the inherent influences of the metal gegenion on the structures, reaction energies, and activation barriers of some representative alkali‐metal compounds. While most comparisons of physical and chemical properties determined experimentally for Group I compounds are precluded due to different substituents, solvents, ligands, etc., ab initio calculations of model compounds can yield intrinsic data that are useful for a better understanding of chemical behavior. For this reason, most of the data reviewed in this article are based on quantum chemical calculations, which are compared with experimental data where available. The gegenion often exercises a substantial influence on the course of “ionic” organo alkali‐metal reactions. The compounds comprising ions of alkali metals and “carbanions” are present in solution as monomeric or aggregated contact ion pairs, or solvent‐separated ion pairs. The gegenion thus changes the electronic and spatial structure of the anion by charge‐localization and pyramidalization. Only through ab initio calculations can results be obtained without the falsifying influences of solvation and aggregation on the structures of the carbanionoid moiety, which otherwise prevent comparisons within a group of the periodic table.
Editor: Zug: Hüthig & Wepf Verlag
Idioma: Inglés

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Are Polar Organometallic Compounds "Carbanions"? The Gegenion Effect on Structure and Energies of Alkali-Metal Compounds

Lambert, Christoph ; von Ragué Schleyer, Paul

Zug: Hüthig & Wepf Verlag

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