Rieke metals

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Rieke metals are a highly reactive metal powders prepared by the methods developed by Reuben D. Rieke. Rieke metals are highly reactive because they have high surfaces areas and lack passivating surface oxides.

The method usually involves reduction of a THF suspension an anhydrous metal chloride with an alkali metal (K, Na, Li).^[1] For example, the preparation of Reike magnesium:

MgCl₂ + 2 K → Mg + 2 KCl

In some cases the reaction is carried out with a catalytic amount of an electron carrier such as napthalene, or by using stoichometric amounts of reducing agents such as lithium naphthalenide. The coprecipitated alkali metal chloride is usually not separated from the highly reactive metal, which is generally used in situ.

[edit] Advantages and disadvantages

The method is straightforward but requires a highly experienced chemist. The starting metal halides must be strictly anhydrous. The use of alkali metals, especially potassium metal, is always dangerous. The resulting reagents are generally pyrophoric, the expected trade-off for a highly reactive metal.

Rieke magnesium reacts with aryl halides at -78 °C to afford the corresponding Grignard reagents, often with considerable selectivity.^[2] 4-Fluorotoluene and Rieke magnesium gives the Grignard reagent.

Rieke zinc reacts with bromoesters to give organozinc reagents of value for the Reformatsky reaction.^[3]

Among the many metals that have been generated by this method are Mg, Ca, Ti, Fe, Co, Ni, Cu, Zn, In.

[edit] External links

• Rieke Metals, the owner of the Rieke brand

[edit] References

1. ^ Rieke, R. D. (1989). "Preparation of organometallic compounds from highly reactive metal powders". Science 246: 1260-1264.
2. ^ Lee, J.-S.; Velarde-Ortiz, R.; Guijarro, A.; Wurst, J. R.; Rieke, R. D., (2000). "Low-Temperature Formation of Functionalized Grignard Reagents from Direct Oxidative Addition of Active Magnesium to Aryl Bromides". Journal of Organic Chemistry 65: 5428-5430. DOI:10.1021/jo000413i.
3. ^ Rieke, R. D.; Hanson, M. V., (1997). "New organometallic reagents using highly reactive metals". Tetrahedron 53: 1925-1956. DOI:10.1016/S0040-4020(96)01097-6.