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 the recipes for their preparation. Among the many metals that have been generated by this method are Mg, Ca, Ti, Fe, Co, Ni, Cu, Zn, and In, which in turn are called Rieke-magnesium, Rieke-calcium, etc.
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.[1]
Rieke originally described three general procedures:
Reaction with molten sodium or potassium in a solvent whose boiling point is higher than the metal's melting point, and which can dissolve some of the anhydrous salt, in an inert atmosphere. Suggested combinations were potassium in tetrahydrofuran (THF), sodium in 1,2-dimethoxyethane, and either metal with benzene or toluene. The exothermic reaction takes a few hours, and usually requires refluxing.[1]
Reaction with an alkali metal at temperatures below its melting point, with a catalytic amount (5-10% by mole) of an electron carrier such as naphthalene[1] or biphenyl.[3] This method can be used with lithium as the reducing agent, even at room temperature, and is therefore less hazardous than the previous method; and often results in more reactive powders.[2]
Reaction with previously prepared lithium naphthalide[1] or lithium biphenylide[3] instead of lithium. This process can be carried out at even lower temperatures, below ambient. Although slower, it was found to produce even smaller particles.[1]
The alkali metal chloride coprecipitates with the finely divided metal, which can be used in situ or separated by washing away the alkali chloride with a suitable solvent.[1]
Usesedit
Rieke zinc has attracted the greatest attention of all the Rieke metals. Interest is motivated by the ability of Rieke Zn to convert 2,5-dibromothiophenes to the corresponding polythiophene.[4] Rieke-Zn also reacts with bromoesters to give organozinc reagents of value for the Reformatsky reaction.[5]
Rieke magnesium reacts with aryl halides, some even at −78 °C, to afford the corresponding Grignard reagents, often with considerable selectivity.[6] Rieke magnesium is famous for enabling the formation of "impossible Grignard reagents" such as those derived from aryl fluorides and from 2-chloronorbornane.[2]
Historyedit
The use of highly reactive metals in chemical synthesis was popularized in the 1960s. One development in this theme is the use of metal vapor synthesis, as described by Skell, Timms, Ozin, and others. All of these methods relied on elaborate instrumentation to vaporize the metals, releasing an atomic form of these reactants.
In 1972, Reuben D. Rieke, a professor of chemistry at the University of North Carolina, published the method that now bears his name.[7] 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.[8]
Safetyedit
Production and use of Rieke metals often involves the handling of highly pyrophoric materials, requiring the use of air-free techniques.
Referencesedit
^ abcdefgRieke, 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.
^ abcRieke, 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.
^ abRieke, 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.
^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.
^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.
^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.
^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.
^(2018): "About Us". Rieke Metals's website, accessed on 2019-03-19.
External linksedit
BASF Organozinc Compounds
Rieke Metals, the owner of the Rieke brand
January 01, 1970
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Not to be confused with Raney nickel 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 the recipes for their preparation Among the many metals that have been generated by this method are Mg Ca Ti Fe Co Ni Cu Zn and In which in turn are called Rieke magnesium Rieke calcium etc 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 mm down to 0 1 mm 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 1 Contents 1 Preparation 2 Uses 3 History 4 Safety 5 References 6 External linksPreparation editRieke metals are usually prepared by a reduction of an anhydrous metal chloride with an alkali metal in a suitable solvent 1 For example Rieke magnesium can be prepared from magnesium chloride with potassium as the reductant 2 MgCl2 2 K Mg 2 KCl Rieke originally described three general procedures Reaction with molten sodium or potassium in a solvent whose boiling point is higher than the metal s melting point and which can dissolve some of the anhydrous salt in an inert atmosphere Suggested combinations were potassium in tetrahydrofuran THF sodium in 1 2 dimethoxyethane and either metal with benzene or toluene The exothermic reaction takes a few hours and usually requires refluxing 1 Reaction with an alkali metal at temperatures below its melting point with a catalytic amount 5 10 by mole of an electron carrier such as naphthalene 1 or biphenyl 3 This method can be used with lithium as the reducing agent even at room temperature and is therefore less hazardous than the previous method and often results in more reactive powders 2 Reaction with previously prepared lithium naphthalide 1 or lithium biphenylide 3 instead of lithium This process can be carried out at even lower temperatures below ambient Although slower it was found to produce even smaller particles 1 The alkali metal chloride coprecipitates with the finely divided metal which can be used in situ or separated by washing away the alkali chloride with a suitable solvent 1 Uses editRieke zinc has attracted the greatest attention of all the Rieke metals Interest is motivated by the ability of Rieke Zn to convert 2 5 dibromothiophenes to the corresponding polythiophene 4 Rieke Zn also reacts with bromoesters to give organozinc reagents of value for the Reformatsky reaction 5 Rieke magnesium reacts with aryl halides some even at 78 C to afford the corresponding Grignard reagents often with considerable selectivity 6 Rieke magnesium is famous for enabling the formation of impossible Grignard reagents such as those derived from aryl fluorides and from 2 chloronorbornane 2 History editThe use of highly reactive metals in chemical synthesis was popularized in the 1960s One development in this theme is the use of metal vapor synthesis as described by Skell Timms Ozin and others All of these methods relied on elaborate instrumentation to vaporize the metals releasing an atomic form of these reactants In 1972 Reuben D Rieke a professor of chemistry at the University of North Carolina published the method that now bears his name 7 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 8 Safety editProduction and use of Rieke metals often involves the handling of highly pyrophoric materials requiring the use of air free techniques References edit a b c d e f g 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 a b c 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 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link Collected Volumes vol 6 p 845 a b 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 a href Template Cite journal html title Template Cite journal cite journal a CS1 maint multiple names authors list link Collected Volumes vol 9 p 9 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 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 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 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 2018 About Us Rieke Metals s website accessed on 2019 03 19 External links editBASF Organozinc Compounds Rieke Metals the owner of the Rieke brand Retrieved from https en wikipedia org w index php title Rieke metal amp oldid 1185552887, wikipedia, wiki, book, books, library,
