Sandwich complexes

from Wikipedia, the free encyclopedia
Structure of ferrocene in the staggered conformation
Structure of ferrocene according to Kealy

As sandwich complexes (also sandwich compound , formerly double-cone connection or double cone structure ) in the narrower sense are in the organometallic chemistry called those main group or transition metal complexes which two parallel, planar wear cyclic organic ligand. These include the metallocenes , compounds with two cyclopentadienyl ligands.

The first sandwich complex ever synthesized was in 1951 ferrocene, which was synthesized in parallel as a coincidental product by two research groups led by T. J. Kealy and P. L. Pauson and S. A. Miller, J. A. Tebboth and J. F. Tremaine . Kealy and Paulson actually aimed at the synthesis of the purely organic fulvalene .

actually planned synthesis of fulvalene according to Kealy

Both working groups initially came up with the same structural proposal, which, however, could not be reconciled with the analytical data. In particular, several signals for the different CH stretching vibrations should appear in the infrared spectrum of the structure proposed by Kealy, but in accordance with the proposal by Fischer and Wilkinson, the compound only shows a single resonance.

The true nature of ferrocene was finally revealed by Ernst Otto Fischer et al. and Geoffrey Wilkinson and Robert B. Woodward independently discovered. Wilkinson and Fischer received the Nobel Prize in Chemistry in 1973 for this achievement and for their life's work in the field of inorganic chemistry. Robert B. Woodward, who did not become a partner in the award in 1973, protested against this disregard for his contribution in a letter to the Nobel Committee in Stockholm that became known later. However, after the discovery of ferrocene, he had turned back to organic synthesis and had already received the Nobel Prize in 1965 for his achievements in this field.

After the clarification of the structure of ferrocene it became known that the chromium salts investigated by Franz Hein in Leipzig and Jena since 1919 were sandwich complexes.

For a long time, research was largely limited to the cyclopentadienyl ligand found in ferrocene. Later examples are the first time in 1955 by Ernst Otto Fischer and Walter Hafner with benzene ligand shown bis (benzene) chromium or synthesized in 1968 uranocene with cyclooctatetraene ligands.

Sandwich complexes are used today especially in asymmetric catalysis to obtain stereoisomerically pure compounds and, in the form of their polymers, show promising approaches for new types of semiconducting materials.

More sandwich complexes

As a half-sandwich complexes refers to those compounds which possess only a cyclopentadienyl system π bonds have bound to a central metal atom. The saturation of free (electron) valences takes place z. B. via carbonyl groups .

Tricarbonyl (η 5 -cyclopentadienyl) manganese

literature