Diphenylchromium Iodides

Several properties reported did not agree with the structures formulated above. These properties include color, golden orange, and magnetic susceptibility, BM, 1.75. 

The magnetic susceptibility determined for the series of compounds tri-, tetra-, and pentaphenylchromium iodide was found to be approximately 

7 BM (indicates one free electron) for each compound. In addition, all compounds have a similar golden orange color while a change in color is characteristic of transition metals going from one valence state to another. Surely (7-bonded chromium in such a series should exhibit different valence states and not just one unpaired electron, as is noted. The UV absorption by chromium ions is characteristic for different valence states. It is clear that the tentative structures cannot account for the same absorption maxima exhibited by compounds [5-42], [5-44], and [5-46]. Reductive decomposition of [5-46] by lithium aluminum hydride gave 2 moles of biphenyl and no benzene. 

Since reductive decomposition of phenyl metals generally gives benzene, it is evident that there is no phenyl group within [5-46]. Upon pyrolysis, [5-46] gives two molecules of biphenyl however, pyrolysis of phenyl metals normally yields biphenyl quantitatively. Therefore, pyrolysis data cannot provide positive evidence of the existence of biphenyl in [5-46]. This case is different than for the tentative assignment of the structure of dibenzene-chromium, where pyrolysis data is sufficient to suggest a 7c-complex bond between benzene and the chromium metal. 

Considering these results along with the abnormal properties previously described, the structure of tetraphenylchromium iodide was reformulated as a TT-complex [5-49]. 

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SYNS BIS(BENZENE)CHROMIUM(l-l-)IODIDE CHROMIUTV I-H), BIS(BENZENE)-, iodide (SCI) (CHROMIUM(l+), BIS(eta )-BENZENE)-, IODIDE (9CI) CHROMIUM, BIS(BENZENE)IODO- CHROMIUM(III), DIPHENYL-, IODIDE DIBENZENECHROMIUM IODIDE DIPHENYLCHROMIUM(III) IODIDE... 

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