Organochromium Chemistry - History

History

The first organochromium compound was described in 1919 by Franz Hein. He treated phenylmagnesium bromide with chromium(III) chloride to give a new product (after hydrolysis) which he incorrectly identified as pentaphenyl chromium bromide (Ph₅CrBr). Years later, in 1957 H.H. Zeiss et al. repeated Hein's experiments and correctly arrived at a cationic bisarene chromium sandwich compound (Ar₂Cr+). Bis(benzene)chromium itself was discovered around the same time in 1956 by Ernst Otto Fischer by reaction of chromium(III) chloride, benzene and aluminum chloride. The related compound chromocene was discovered a few years earlier in 1953 also by Fischer.

In another development, Anet and Leblanc also in 1957 prepared a benzyl chromium solution from benzyl bromide and chromium(II) perchlorate. This reaction involves one-electron oxidative addition of the carbon-bromine bond, a process which was shown by Kochi to be a case of double single electron transfer, first to give the benzyl free radical and then to the benzyl anion.

G. Wilke et al. introduced tris-(η-allyl)chromium in 1963 as an early Ziegler-Natta catalyst (but not successful in the long run) Chromocene compounds were first employed in ethylene polymerization in 1972 by Union Carbide and continue to used today in the industrial production of high-density polyethylene.

The organochromium compound (phenylmethoxycarbene)pentacarbonylchromium, Ph(OCH₃)C=Cr(CO)₅ was the first carbene complex to be crystallographically characterized by Fischer in 1967 (now called a Fischer carbene). The first ever carbyne, this one also containing chromium, made its debut in 1973.

The first example of a proposed metal-metal quintuple bond is found in a compound of the type ₂, where Ar is a bulky aryl ligand.