Formation by Six-Membered Ring Systems

In 1954 a new synthesis for chromium carbonyl was developed in collaboration wdth W. Hafner. The system CrCls/AlCla/Al/CeHe/CO used in this case was found, when the reaction was more closely studied, to open the way to the compound CrfCgHels 53). It was shown that in an autoclave at 180°, without the carbon monoxide, a mixture resulted which contained the [Cr (CeH8)2] cation, produced as followrs  

The cation could be isolated by precipitation as the picrate or the reineckate. By reduction with sodium dithionite it could be converted directly into brown-black dibenzene chromium, Cr(C6He)2, w hich can be sublimed 53,54)  

This process is analogous to the preparation of ferrocene from ferricinium ions. It was soon possible to extend the work to the preparation of a 

The synthesis from metal chloride, aluminum chloride, the aromatic compound, and aluminum powder (in those cases where reduction was 

A further synthesis of metal complexes containing two six-membered aromatic rings, which was limited to chromium, was based on the interaction of phenyl magnesium bromide and chromic chloride, and subsequent hydrolysis of the reaction mixture to the [Cr(C8He)2] cation (107, m, m). 

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