With metal halides ferric chloride

The initial tests of the sodium dispersion-metal halide system were made with ferric chloride, fortunately, and with a nonaqueous solvent in which ferric chloride was soluble. Thus, ferric chloride was present as a solution and, consequently, presented maximum surface for contact with the sodium particles. This feature, coupled with the lower activation energy requirements, permitted the reaction to proceed at temperatures well below room temperature and established the operability of the method. The success of the initial (ferric chloride) tests lent encouragement to tests on other metal systems and prompted continued investigations when the initial runs at lower temperatures failed. The discovery of the threshold, or trigger, temperature for nickel (II) chloride reduction paved the way for successful reduction of other metal halides such as manganese (II) chloride, cobalt (II) chloride, and cadmium bromide. 

The reaction of the appropriate Grignard reagent with selected transition metal halides provides a very useful method for the preparation of many cyclopentadienyl and arene Tc-complexes. The reaction of cyclopentadienyl-magnesium bromide with ferric chloride constituted the original method for the preparation of ferrocene (2-26). 

Azobenzene treated with LiAlH4 in ether at room temp, in the presence of a trace of a metal salt, e.g. ferric or cuprous chloride hydrazobenzene. Y ca. 100%.— The reductions are very fast and generally completed in less than 10 min. whereas they proceed with difficulty in the absence of catalysts.—Similarly Nitrobenzene hydrazobenzene. Y 90% or better.—Al-halides are inactive. F. e. and metal salts s. G. A. Olah, Am. Soc. 81, 3165 (1959). 

Oxidizing metal ions with chlorides are aggressive pitters. Cupric, ferric, and mercuric halides are extremely aggressive even our most corrosion-resistant alloys can be pitted by CuClj and FeClj. 

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