Diarene metal -complexes

Table 4-27. Magnetic Moments of Diarene Metal -Complexes...

The magnetic moments of metallocenes and di-7c-cyclopentadienyl metal complexes are very similar to diarene metal complexes. The magnetic data of some metallocenes are shown in Table 4-29. 

Diarene metals generally decompose under conditions of normal electrophilic substitution, but dibenzene chromium can be metalated with amyl sodium in alkanes, and subsequent reaction with carbon dioxide and dimethyl sulfate results in a complex mixture of mono-, di-, and poly-substituted dibenzene chromium methyl esters. It is interesting that these polysubstituted compounds are homoannular in contrast to the corresponding ferrocene compounds. In view of the scanty evidence and ease of oxidation, it is impossible to conclude whether the diarene metals are less aromatic than the dicyclopentadienyl metals as predicted by simple theory (Sec. III.A). 

For simplicity, we shall illustrate the basic theoretical methods employed in model calculations by an idealized case of the interaction between a substituted benzene, C6H5X, and a transition-metal atom such as chromium. This treatment is then readily extended to either a diarene complex or a monoarene complex such as a tricarbonylarene metal. 

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