Transition metal 7r complexes

As was suggested in the preceding discussion, most of the arene complexes isolated by metal-atom techniques are benzene derivatives. However, heterocyclic ligands are also known to act as 5- or 6-electron donors in transition-metal 7r-complexes (79), and it has proved possible to isolate heterocyclic complexes via the metal-atom route. Bis(2,6-di-methylpyridine)Cr(O) was prepared by cocondensation of Cr atoms with the ligand at 77 K (79). The red-brown product was isolated in only 2% yield the stoichiometry was confirmed by mass spectrometry, and the structure determined by X-ray crystal-structure analysis, which supported a sandwich formulation. 

From phosphorus heterocycles to phosphorus analogues of unsaturated hydrocarbon-transition metal 7r-complexes. J. Organomet. Chem. 400, 149 (1990). 

Keto Derivatives of Group IV Organometalloids, 7, 95 Lewis Base-Metal Carbonyl Complexes, 3, 181 Ligand Substitution in Transition Metal 7r-Complexes, 10, 347 Literature of Organo-Transition Metal Chemistry 1950-1970, 10, 273 Literature of Organo-Transition Metal Chemistry 1971, 11, 447 Literature of Organo-Transition Metal Chemistry 1972, 12, 379 Mass Spectra of Metallocenes and Related Compounds, 8, 211 Mass Spectra of Organometallic Compounds, 6, 273... 

The key of this success lies in the opening of the synthesis in which Roush and Wada utilize the various possibilities offered by the buta-diene-Fe(CO), chemistry for acyclic stereocontrol. They thus impressively demonstrate that the use of transition metal 7r-complexes as synthetic building blocks opens new and powerful strategies for the synthesis of complex target molecules. 

Although quantitative studies of substitution reactions have only been launched quite recently, a considerable body of experimental data is available, so that theoretical principles of ligand substitution mechanisms in classical inorganic complexes have been developed. Unfortunately the same cannot be said for substitution reactions involving 7r-bonded hydrocarbon ligands, in spite of a continuously expanding number of publications in this field. In the majority of studies substitution reactions are used to obtain novel transition metal 7r-complexes, and a far lesser number of papers deal with the quantitative aspects of the exchange. 

Noble gas formalism or, as it is more commonly referred to, the effective atomic number (FAN) rule is a useful guideline for predicting the stoichoi-metries of transition metal 7r-complexes. 

Magnetic measurements find intensive applications in the study of transitional metal 7r-complexes. Such data can give information that is useful for the elucidation of valency, bond type, and stereochemistry of such compounds. 

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