Zinc

This chapter discusses the formation of Rieke zinc; for the first time, this zinc was shown to add oxidatively to alkyl and aryl bromides. The Rieke zinc used in those reactions was prepared using anhydrous zinc chloride or zinc bromide and potassium or sodium metal in refluxing tetrahydrofuran (THF) or 1,2-dimethoxyethane (DME) for 4 h. A far superior method of preparing the highly reactive zinc is to use lithium metal as the reducing agent along with an electron carrier such as naphthalene. The first report of the oxidative addition of zinc metal to organic halides dates back to the work of Frankland. He discovered that dialkylz-inc compounds could be prepared from zinc metal and methyl iodide or ethyl iodide. However, the reaction did not proceed with alkyl bromides or chlorides. Also, no aryl halides were found to undergo the oxidative addition reaction.