Rieke metal

Group specially prepared, highly reactive metal powder

A Rieke metal is a highly reactive metal powder generated by reduction of a metal salt with an alkali metal. These materials are named after Reuben D. Rieke, who first described along with an associate in 1972 the recipes for their preparation.^[1] In 1974 he told about Rieke-magnesium.^[2] A 1989 paper by Rieke lists several metals that are allowed by the periodic table to be produced by his process: Cd, Zn, Ni, Pt, Pd, Fe, In, Tl, Co, Cr, Mo, W, Cu, which in turn are called Rieke-nickel, Rieke-platinum, etc.^[3]

Highly reactive activated magnesium (Rieke magnesium)

Rieke metals are highly reactive because they have high surface area and lack surface oxides that can retard reaction of bulk materials. The particles are very small, ranging from 1-2 μm down to 0.1 μm or less. Some metals like nickel and copper give black colloidal suspensions that do not settle, even with centrifugation, and cannot be filtered. Other metals such as magnesium and cobalt give larger particles, but these are found to be composed mainly of the alkali salt by-product, with the metal dispersed in them as much finer particles or even as an amorphous phase.^[3]

Preparation

Rieke metals are usually prepared by a reduction of an anhydrous metal chloride with an alkali metal, in a suitable solvent.^[4][3] For example, Rieke magnesium can be prepared from magnesium chloride with potassium as the reductant:^[5][6][4]

MgCl₂ + 2 K → Mg + 2 KCl

Rieke originally described three general procedures:

• Reacción con sodio o potasio fundido en un disolvente cuyo punto de ebullición es superior al punto de fusión del metal, y que puede disolver parte de la sal anhidra, en atmósfera inerte . Las combinaciones sugeridas fueron potasio en tetrahidrofurano (THF), sodio en 1,2-dimetoxietano y metal con benceno o tolueno . La reacción exotérmica dura unas horas y normalmente requiere reflujo . ^[3]
• Reacción con un metal alcalino a temperaturas inferiores a su punto de fusión, con una cantidad catalítica (5-10% en mol) de un portador de electrones como naftaleno ^[3] o bifenilo . ^[7] Este método se puede utilizar con litio como agente reductor, incluso a temperatura ambiente, y por lo tanto es menos peligroso que el método anterior; y a menudo da como resultado polvos más reactivos. ^[5]
• ^{Reacción con naftalida de litio [3]} o bifeniluro de litio ^[7] previamente preparada en lugar de litio. Este proceso se puede llevar a cabo a temperaturas aún más bajas, por debajo de la temperatura ambiente. Aunque más lento, se descubrió que producía partículas aún más pequeñas. ^[3]

El cloruro de metal alcalino coprecipita con el metal finamente dividido, que puede usarse in situ o separarse lavando el cloruro alcalino con un disolvente adecuado. ^[3]

Usos

De todos los metales de Rieke, el zinc de Rieke ha atraído la mayor atención. El interés está motivado por la capacidad de Rieke Zn para convertir 2,5-dibromotiofenos en el correspondiente politiofeno . ^[8] Rieke-Zn también reacciona con bromoésteres para dar reactivos de organozinc valiosos para la reacción de Reformatsky . ^[9]

El magnesio de Rieke reacciona con haluros de arilo, algunos incluso a -78 °C, para producir los reactivos de Grignard correspondientes , a menudo con una selectividad considerable. ^[10] El magnesio de Rieke es famoso por permitir la formación de "reactivos de Grignard imposibles", como los derivados de los fluoruros de arilo y del 2-cloronorbornano. ^[5]

Historia

El uso de metales altamente reactivos en la síntesis química se popularizó en los años 1960. Un desarrollo en este tema es el uso de la síntesis de vapor metálico , como lo describen Skell, ^{[ cita necesaria ]} Timms, ^[11] Ozin, ^{[ cita necesaria ]} y otros. Todos estos métodos se basaban en instrumentación elaborada para vaporizar los metales, liberando una forma atómica de estos reactivos.

In 1972, Reuben D. Rieke, a professor of chemistry at the University of North Carolina, published the method that now bears his name.^[12] In contrast to previous methods, it did not require special equipment, and the main challenges were only the handling of pyrophoric reagents and/or products, and the need for anhydrous reagents and air-free techniques. Thus his discovery gained much attention because of its simplicity and the reactivity of the activated metals.

Rieke continued this work at the University of Nebraska-Lincoln. He and his wife Loretta founded Rieke Metals LLC in 1991, based on these materials.^[13]

Safety

Production and use of Rieke metals often involves the handling of highly pyrophoric materials, requiring the use of air-free techniques.

References

1. Rieke, Reuben (2017). "Magnesium". Chemical Synthesis Using Highly Reactive Metals. pp. 161–208. doi:10.1002/9781118929124.ch4. ISBN 978-1-118-92911-7.
2. Rieke, Reuben D.; Bales, Stephen E. (1974). "ChemInform Abstract: ACTIVATED METALS PART 4, PREPARATION AND REACTIONS OF HIGHLY REACTIVE MAGNESIUM METAL". Chemischer Informationsdienst. 5 (21). doi:10.1002/chin.197421315.
3. Rieke, R. D. (1989). "Preparation of Organometallic Compounds from Highly Reactive Metal Powders". Science. 246 (4935): 1260–1264. Bibcode:1989Sci...246.1260R. doi:10.1126/science.246.4935.1260. PMID 17832221. S2CID 92794.
4. Rieke, Reuben D.; Sell, Matthew S.; Klein, Walter R.; Chen, Tian-An; Brown, Jeffrey D.; Hanson, Mark V. (1995). "Rieke Metals: Highly Reactive Metal Powders Prepared by Alkali Metal Reduction of Metal Salts". Active Metals. pp. 1–59. doi:10.1002/9783527615179.ch01. ISBN 978-3-527-29207-3.
5. Rieke, R. D.; Bales, S. E.; Hudnall, P. M.; Burns, T. P.; Poindexter, G S. (1988). "Highly Reactive Magnesium for the Preparation of Grignard Reagents: 1-Norbornane Acid". Organic Syntheses{{cite journal}}: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 6, p. 845.
6. Angew Chem Int Ed Engl - February 1993 - Alois Furstner - Chemistry of and with Highly Reactive Metals
7. Rieke, R. D.; Wu, T.-C.; Rieke, L. I. (1998). "Highly Reactive Calcium for the Preparation of Organocalcium Reagents: 1-Adamantyl Calcium Halides and Their Addition to Ketones: 1-(1-Adamantyl)cyclohexanol"". Organic Syntheses{{cite journal}}: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 9, p. 9.
8. Chen, T.-A.; Wu, X.; Rieke, R. D. (1995). "Regiocontrolled Synthesis of Poly(3-alkylthiophenes) Mediated by Rieke Zinc: Their Characterization and Solid-State Properties". Journal of the American Chemical Society. 117: 233–244. doi:10.1021/ja00106a027.
9. Rieke, R. D.; Hanson, M. V. (1997). "New Organometallic Reagents Using Highly Reactive Metals". Tetrahedron. 53 (6): 1925–1956. doi:10.1016/S0040-4020(96)01097-6.
10. 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 (17): 5428–5430. doi:10.1021/jo000413i. PMID 10993378.
11. Peter L. Timms, "New Developments in Making Compounds and Materials by Condensing Gaseous High-temperature Species at Atmospheric or Low Pressure". School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
12. Reuben D. Rieke, Phillip M. Hudnall (1972). "Activated Metals. I. Preparation of Highly reactive magnesium metal". J. Am. Chem. Soc. 94 (20): 7178–7179. doi:10.1021/ja00775a066.
13. (2018): "About Us". Rieke Metals's website, accessed on 2019-03-19.

External links

• BASF Organozinc Compounds
• Rieke Metals, the owner of the Rieke brand