Grignard reagent

Last updated
Usually Grignard reagents are written as R-Mg-X, but in fact the magnesium(II) centre is tetrahedral when dissolved in Lewis basic solvents, as shown here for the bis-adduct of methylmagnesium chloride and THF. Methylmagnesium-chloride-THF-3D-balls.png
Usually Grignard reagents are written as R-Mg-X, but in fact the magnesium(II) centre is tetrahedral when dissolved in Lewis basic solvents, as shown here for the bis-adduct of methylmagnesium chloride and THF.

Grignard reagents or Grignard compounds are chemical compounds with the general formula R−Mg−X, where X is a halogen and R is an organic group, normally an alkyl or aryl. Two typical examples are methylmagnesium chloride Cl−Mg−CH3 and phenylmagnesium bromide (C6H5)−Mg−Br. They are a subclass of the organomagnesium compounds.

Contents

Grignard compounds are popular reagents in organic synthesis for creating new carbon–carbon bonds. For example, when reacted with another halogenated compound R'−X' in the presence of a suitable catalyst, they typically yield R−R' and the magnesium halide MgXX' as a byproduct; and the latter is insoluble in the solvents normally used. In this aspect, they are similar to organolithium reagents.

Grignard reagents are rarely isolated as solids. Instead, they are normally handled as solutions in solvents such as diethyl ether or tetrahydrofuran using air-free techniques. Grignard reagents are complex with the magnesium atom bonded to two ether ligands as well as the halide and organyl ligands.

The discovery of the Grignard reaction in 1900 was recognized with the Nobel Prize awarded to Victor Grignard in 1912.

Synthesis

From Mg metal

Traditionally Grignard reagents are prepared by treating an organic halide (normally organobromine) with magnesium metal. Ethers are required to stabilize the organomagnesium compound. Water and air, which rapidly destroy the reagent by protonolysis or oxidation, are excluded. [1] Although the reagents still need to be dry, ultrasound can allow Grignard reagents to form in wet solvents by activating the magnesium such that it consumes the water. [2]

As is common for reactions involving solids and solution, the formation of Grignard reagents is often subject to an induction period. During this stage, the passivating oxide on the magnesium is removed. After this induction period, the reactions can be highly exothermic. This exothermicity must be considered when a reaction is scaled-up from laboratory to production plant. [3] Most organohalides will work, but carbon-fluorine bonds are generally unreactive, except with specially activated magnesium (through Rieke metals).

Magnesium

Typically the reaction to form Grignard reagents involves the use of magnesium ribbon. All magnesium is coated with a passivating layer of magnesium oxide, which inhibits reactions with the organic halide. Many methods have been developed to weaken this passivating layer, thereby exposing highly reactive magnesium to the organic halide. Mechanical methods include crushing of the Mg pieces in situ, rapid stirring, and sonication. [4] Iodine, methyl iodide, and 1,2-dibromoethane are common activating agents. The use of 1,2-dibromoethane is advantageous as its action can be monitored by the observation of bubbles of ethylene. Furthermore, the side-products are innocuous:

Mg + BrC2H4Br → C2H4 + MgBr2

The amount of Mg consumed by these activating agents is usually insignificant. A small amount of mercuric chloride will amalgamate the surface of the metal, enhancing its reactivity. Addition of preformed Grignard reagent is often used as the initiator.

Specially activated magnesium, such as Rieke magnesium, circumvents this problem. [5] The oxide layer can also be broken up using ultrasound, using a stirring rod to scratch the oxidized layer off, [6] or by adding a few drops of iodine or 1,2-Diiodoethane. Another option is to use sublimed magnesium or magnesium anthracene. [7]

"Rieke magnesium" is prepared by a reduction of an anhydrous magnesium chloride with an potassium:

MgCl2 + 2 K → Mg + 2 KCl

Mechanism

In terms of mechanism, the reaction proceeds through single electron transfer: [8] [9] [10]

Mg transfer reaction (halogen–Mg exchange)

An alternative preparation of Grignard reagents involves transfer of Mg from a preformed Grignard reagent to an organic halide. Other organomagnesium reagents are used as well. [11] This method offers the advantage that the Mg transfer tolerates many functional groups. An illustrative reaction involves isopropylmagnesium chloride and aryl bromide or iodides: [12]

i-PrMgCl + ArCl → i-PrCl + ArMgCl

From alkylzinc compounds (reductive transmetalation)

A further method to synthesize Grignard reagents involves reaction of Mg with an organozinc compound. This method has been used to make adamantane-based Grignard reagents, which are, due to C-C coupling side reactions, difficult to make by the conventional method from the alkyl halide and Mg. The reductive transmetalation achieves: [13]

AdZnBr + Mg → AdMgBr + Zn

Testing Grignard reagents

Because Grignard reagents are so sensitive to moisture and oxygen, many methods have been developed to test the quality of a batch. Typical tests involve titrations with weighable, anhydrous protic reagents, e.g. menthol in the presence of a color-indicator. The interaction of the Grignard reagent with phenanthroline or 2,2'-biquinoline causes a color change. [14]

Reactions of Grignard reagents

Grignard reagent reactions
Named after Victor Grignard
Reaction type Coupling reaction
Reaction
Carbon electrophiles
+
R-MgX
+
(H3O+)
Coupling Product

With carbonyl compounds

Grignard reagents react with a variety of carbonyl derivatives. [15]

Reactions of Grignard reagents with carbonyls Grignard with carbonyl.png
Reactions of Grignard reagents with carbonyls

The most common application of Grignard reagents is the alkylation of aldehydes and ketones, i.e. the Grignard reaction: [16]

Reaction of
CH3C(=O)CH(OCH3)2 with
H2C=CHMgBr GrignardReactionVinylation.png
Reaction of CH3C(=O)CH(OCH3)2 with H2C=CHMgBr

Note that the acetal functional group (a protected carbonyl) does not react.

Such reactions usually involve an aqueous acidic workup, though this step is rarely shown in reaction schemes. In cases where the Grignard reagent is adding to an aldehyde or a prochiral ketone, the Felkin-Anh model or Cram's Rule can usually predict which stereoisomer will be formed. With easily deprotonated 1,3-diketones and related acidic substrates, the Grignard reagent RMgX functions merely as a base, giving the enolate anion and liberating the alkane RH.

Grignard reagents are nucleophiles in nucleophilic aliphatic substitutions for instance with alkyl halides in a key step in industrial Naproxen production:

Naproxen synthesis Naproxen synthesis.png
Naproxen synthesis

Grignard reagents also react with many "carbonyl-like" compounds and other electrophiles:

Reactions of Grignard reagents with various electrophiles Grignard with others.png
Reactions of Grignard reagents with various electrophiles

Reactions as a base

Grignard reagents serve as a base for non-protic substrates (this scheme does not show workup conditions, which typically includes water). Grignard reagents are basic and react with alcohols, phenols, etc. to give alkoxides (ROMgBr). The phenoxide derivative is susceptible to formylation by paraformaldehyde to give salicylaldehyde. [17]

Alkylation of metals and metalloids

Like organolithium compounds, Grignard reagents are useful for forming carbon–heteroatom bonds.

Grignard reagents react with many metal-based electrophiles. For example, they undergo transmetallation with cadmium chloride (CdCl2) to give dialkylcadmium: [18]

2 RMgX + CdCl2 → R2Cd + 2 Mg(X)Cl

Schlenk equilibrium

Most Grignard reactions are conducted in ethereal solvents, especially diethyl ether and THF. Grignard reagents react with 1,4-dioxane to give the diorganomagnesium compounds and insoluble coordination polymer MgX2(dioxane)2 and (R = organic group, X = halide):

2 RMgX + dioxane ⇌ R2Mg + MgX2(dioxane)2

This reaction exploits the Schlenk equilibrium, driving it toward the right.

Precursors to magnesiates

Grignard reagents react with organolithium compounds to give ate complexes (Bu = butyl): [19]

BuMgBr + 3 BuLi → LiMgBu3 + BuBr

Coupling with organic halides

Grignard reagents do not typically react with organic halides, in contrast with their high reactivity with other main group halides. In the presence of metal catalysts, however, Grignard reagents participate in C-C coupling reactions. For example, nonylmagnesium bromide reacts with methyl p-chlorobenzoate to give p-nonylbenzoic acid, in the presence of Tris(acetylacetonato)iron(III) (Fe(acac)3), after workup with NaOH to hydrolyze the ester, shown as follows. Without the Fe(acac)3, the Grignard reagent would attack the ester group over the aryl halide. [20]

4-nonylbenzoicacid synthesis using a grignard reagent 4nonylbenzoicacidSynthesis.svg
4-nonylbenzoicacid synthesis using a grignard reagent

For the coupling of aryl halides with aryl Grignard reagents, nickel chloride in tetrahydrofuran (THF) is also a good catalyst. Additionally, an effective catalyst for the couplings of alkyl halides is the Gilman catalyst lithium tetrachlorocuprate (Li2CuCl4), prepared by mixing lithium chloride (LiCl) and copper(II) chloride (CuCl2) in THF. The Kumada-Corriu coupling gives access to [substituted] styrenes.

Oxidation

Treatment of a Grignard reagent with oxygen gives the magnesium organoperoxide. Hydrolysis of this material yields hydroperoxides or alcohol. These reactions involve radical intermediates.

The simple oxidation of Grignard reagents to give alcohols is of little practical importance as yields are generally poor. In contrast, two-step sequence via a borane (vide supra) that is subsequently oxidized to the alcohol with hydrogen peroxide is of synthetic utility.

The synthetic utility of Grignard oxidations can be increased by a reaction of Grignard reagents with oxygen in presence of an alkene to an ethylene extended alcohol. [21] This modification requires aryl or vinyl Grignards. Adding just the Grignard and the alkene does not result in a reaction demonstrating that the presence of oxygen is essential. The only drawback is the requirement of at least two equivalents of Grignard although this can partly be circumvented by the use of a dual Grignard system with a cheap reducing Grignard such as n-butylmagnesium bromide.

Grignard oxygen oxidation example Grignard oxidation example.png
Grignard oxygen oxidation example

Elimination

In the Boord olefin synthesis, the addition of magnesium to certain β-haloethers results in an elimination reaction to the alkene. This reaction can limit the utility of Grignard reactions.

Boord olefin synthesis, X = Br, I, M = Mg, Zn BoordReactionOverview.png
Boord olefin synthesis, X = Br, I, M = Mg, Zn

Industrial use

An example of the Grignard reaction is a key step in the (non-stereoselective) industrial production of Tamoxifen [22] (currently used for the treatment of estrogen receptor positive breast cancer in women): [23]

Tamoxifen production TamoxifenSynthesisGrignard.svg
Tamoxifen production

See also

Related Research Articles

<span class="mw-page-title-main">Haloalkane</span> Group of chemical compounds derived from alkanes containing one or more halogens

The haloalkanes are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely used commercially. They are used as flame retardants, fire extinguishants, refrigerants, propellants, solvents, and pharmaceuticals. Subsequent to the widespread use in commerce, many halocarbons have also been shown to be serious pollutants and toxins. For example, the chlorofluorocarbons have been shown to lead to ozone depletion. Methyl bromide is a controversial fumigant. Only haloalkanes that contain chlorine, bromine, and iodine are a threat to the ozone layer, but fluorinated volatile haloalkanes in theory may have activity as greenhouse gases. Methyl iodide, a naturally occurring substance, however, does not have ozone-depleting properties and the United States Environmental Protection Agency has designated the compound a non-ozone layer depleter. For more information, see Halomethane. Haloalkane or alkyl halides are the compounds which have the general formula "RX" where R is an alkyl or substituted alkyl group and X is a halogen.

<span class="mw-page-title-main">Alkylation</span> Transfer of an alkyl group from one molecule to another

Alkylation is a chemical reaction that entails transfer of an alkyl group. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene. Alkylating agents are reagents for effecting alkylation. Alkyl groups can also be removed in a process known as dealkylation. Alkylating agents are often classified according to their nucleophilic or electrophilic character. In oil refining contexts, alkylation refers to a particular alkylation of isobutane with olefins. For upgrading of petroleum, alkylation produces a premium blending stock for gasoline. In medicine, alkylation of DNA is used in chemotherapy to damage the DNA of cancer cells. Alkylation is accomplished with the class of drugs called alkylating antineoplastic agents.

In organic chemistry, an aryl halide is an aromatic compound in which one or more hydrogen atoms, directly bonded to an aromatic ring are replaced by a halide. Haloarenes are different from haloalkanes because they exhibit many differences in methods of preparation and properties. The most important members are the aryl chlorides, but the class of compounds is so broad that there are many derivatives and applications.

<span class="mw-page-title-main">Victor Grignard</span> French chemist (1871–1935)

Francois Auguste Victor Grignard was a French chemist who won the Nobel Prize for his discovery of the eponymously named Grignard reagent and Grignard reaction, both of which are important in the formation of carbon–carbon bonds. He also wrote some of his experiments in his laboratory notebooks.

Metalation is a chemical reaction that forms a bond to a metal. This reaction usually refers to the replacement of a halogen atom in an organic molecule with a metal atom, resulting in an organometallic compound. In the laboratory, metalation is commonly used to activate organic molecules during the formation of C—X bonds, which are necessary for the synthesis of many organic molecules.

The Hiyama coupling is a palladium-catalyzed cross-coupling reaction of organosilanes with organic halides used in organic chemistry to form carbon–carbon bonds. This reaction was discovered in 1988 by Tamejiro Hiyama and Yasuo Hatanaka as a method to form carbon-carbon bonds synthetically with chemo- and regioselectivity. The Hiyama coupling has been applied to the synthesis of various natural products.

The Corey–House synthesis (also called the Corey–Posner–Whitesides–House reaction and other permutations) is an organic reaction that involves the reaction of a lithium diorganylcuprate () with an organic halide or pseudohalide () to form a new alkane, as well as an ill-defined organocopper species and lithium (pseudo)halide as byproducts.

The Schlenk equilibrium, named after its discoverer Wilhelm Schlenk, is a chemical equilibrium taking place in solutions of Grignard reagents and Hauser bases

<span class="mw-page-title-main">Indium(III) chloride</span> Chemical compound

Indium(III) chloride is the chemical compound with the formula InCl3 which forms a tetrahydrate. This salt is a white, flaky solid with applications in organic synthesis as a Lewis acid. It is also the most available soluble derivative of indium. This is one of three known indium chlorides.

The Negishi coupling is a widely employed transition metal catalyzed cross-coupling reaction. The reaction couples organic halides or triflates with organozinc compounds, forming carbon-carbon bonds (C-C) in the process. A palladium (0) species is generally utilized as the catalyst, though nickel is sometimes used. A variety of nickel catalysts in either Ni0 or NiII oxidation state can be employed in Negishi cross couplings such as Ni(PPh3)4, Ni(acac)2, Ni(COD)2 etc.

<span class="mw-page-title-main">Organocopper chemistry</span> Compound with carbon to copper bonds

Organocopper chemistry is the study of the physical properties, reactions, and synthesis of organocopper compounds, which are organometallic compounds containing a carbon to copper chemical bond. They are reagents in organic chemistry.

<span class="mw-page-title-main">Group 2 organometallic chemistry</span>

Group 2 organometallic chemistry refers to the organic derivativess of any group 2 element. It is a subtheme to main group organometallic chemistry. By far the most common group 2 organometallic compounds are the magnesium-containing Grignard reagents which are widely used in organic chemistry. Other organometallic group 2 compounds are typically limited to academic interests.

<span class="mw-page-title-main">Tetramethyltin</span> Chemical compound

Tetramethyltin is an organometallic compound with the formula (CH3)4Sn. This liquid, one of the simplest organotin compounds, is useful for transition-metal mediated conversion of acid chlorides to methyl ketones and aryl halides to aryl methyl ketones. It is volatile and toxic, so care should be taken when using it in the laboratory.

Organomanganese chemistry is the chemistry of organometallic compounds containing a carbon to manganese chemical bond. In a 2009 review, Cahiez et al. argued that as manganese is cheap and benign, organomanganese compounds have potential as chemical reagents, although currently they are not widely used as such despite extensive research.

<span class="mw-page-title-main">Organobismuth chemistry</span>

Organobismuth chemistry is the chemistry of organometallic compounds containing a carbon to bismuth chemical bond. Applications are few. The main bismuth oxidation states are Bi(III) and Bi(V) as in all higher group 15 elements. The energy of a bond to carbon in this group decreases in the order P > As > Sb > Bi. The first reported use of bismuth in organic chemistry was in oxidation of alcohols by Frederick Challenger in 1934 (using Ph3Bi(OH)2). Knowledge about methylated species of bismuth in environmental and biological media is limited.

In organic chemistry, dehalogenation is a set of chemical reactions that involve the cleavage of carbon-halogen bonds; as such, it is the inverse reaction of halogenation. Dehalogenations come in many varieties, including defluorination, dechlorination, debromination, and deiodination. Incentives to investigate dehalogenations include both constructive and destructive goals. Complicated organic compounds such as pharmaceutical drugs are occasionally generated by dehalogenation. Many organohalides are hazardous, so their dehalogenation is one route for their detoxification.

<span class="mw-page-title-main">Phenylsodium</span> Chemical compound

Phenylsodium C6H5Na is an organosodium compound. Solid phenylsodium was first isolated by Nef in 1903. Although the behavior of phenylsodium and phenyl magnesium bromide are similar, the organosodium compound is very rarely used.

Tamejiro Hiyama is a Japanese organic chemist. He is best known for his work in developing the Nozaki-Hiyama-Kishi reaction and the Hiyama coupling. He is currently a professor at the Chuo University Research and Development Initiative, and a Professor Emeritus of Kyoto University.

<span class="mw-page-title-main">Isopropylmagnesium chloride</span> Chemical compound

Isopropylmagnesium chloride is an organometallic compound with the general formula (CH3)2HCMgCl. This highly flammable, colorless, and moisture sensitive material is the Grignard reagent derived from isopropyl chloride. It is commercially available, usually as a solution in tetrahydrofuran.

In organometallic chemistry, metal–halogen exchange is a fundamental reaction that converts an organic halide into an organometallic product. The reaction commonly involves the use of electropositive metals and organochlorides, bromides, and iodides. Particularly well-developed is the use of metal–halogen exchange for the preparation of organolithium compounds.

References

  1. Goebel, M. T.; Marvel, C. S. (1933). "The Oxidation of Grignard Reagents". Journal of the American Chemical Society. 55 (4): 1693–1696. doi:10.1021/ja01331a065.
  2. Smith, David H. (1999). "Grignard Reactions in "Wet" Ether". Journal of Chemical Education. 76 (10): 1427. Bibcode:1999JChEd..76.1427S. doi:10.1021/ed076p1427.
  3. Philip E. Rakita (1996). "5. Safe Handling Practices of Industrial Scale Grignard Ragents" (Google Books excerpt). In Gary S. Silverman; Philip E. Rakita (eds.). Handbook of Grignard reagents. CRC Press. pp. 79–88. ISBN   0-8247-9545-8.
  4. Smith, David H. (1999). "Grignard Reactions in "Wet" Ether". Journal of Chemical Education. 76 (10): 1427. Bibcode:1999JChEd..76.1427S. doi:10.1021/ed076p1427.
  5. 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.
  6. Clayden, Jonathan; Greeves, Nick (2005). Organic chemistry . Oxford: Oxford Univ. Press. pp.  212. ISBN   978-0-19-850346-0.
  7. Wakefield, Basil J. (1995). Organomagnesium Methods in Organic Chemistry. Academic Press. pp. 21–25. ISBN   0080538177.
  8. Garst, J. F.; Ungvary, F. "Mechanism of Grignard reagent formation". In Grignard Reagents; Richey, R. S., Ed.; John Wiley & Sons: New York, 2000; pp 185–275. ISBN   0-471-99908-3.
  9. Advanced Organic chemistry Part B: Reactions and Synthesis F.A. Carey, R.J. Sundberg 2nd Ed. 1983. Page 435
  10. Garst, J.F.; Soriaga, M.P. "Grignard reagent Formation", Coord. Chem. Rev. 2004, 248, 623 - 652. doi:10.1016/j.ccr.2004.02.018.
  11. Arredondo, Juan D.; Li, Hongmei; Balsells, Jaume (2012). "Preparation of t-Butyl-3-Bromo-5-Formylbenzoate Through Selective Metal-Halogen Exchange Reactions". Organic Syntheses. 89: 460. doi: 10.15227/orgsyn.089.0460 .
  12. Knochel, P.; Dohle, W.; Gommermann, N.; Kneisel, F. F.; Kopp, F.; Korn, T.; Sapountzis, I.; Vu, V. A. (2003). "Highly Functionalized Organomagnesium Reagents Prepared through Halogen–Metal Exchange". Angewandte Chemie International Edition. 42 (36): 4302–4320. doi:10.1002/anie.200300579. PMID   14502700.
  13. Armstrong, D.; Taullaj, F.; Singh, K.; Mirabi, B.; Lough, A. J.; Fekl, U. (2017). "Adamantyl Metal Complexes: New Routes to Adamantyl Anions and New Transmetallations". Dalton Transactions. 46 (19): 6212–6217. doi:10.1039/C7DT00428A. PMID   28443859.
  14. Krasovskiy, Arkady; Knochel, Paul (2006). "Convenient Titration Method for Organometallic Zinc, Harshal ady Magnesium, and Lanthanide Reagents". Synthesis. 2006 (5): 890–891. doi:10.1055/s-2006-926345.
  15. Henry Gilman and R. H. Kirby (1941). "Butyric acid, α-methyl-". Organic Syntheses ; Collected Volumes, vol. 1, p. 361.
  16. Haugan, Jarle André; Songe, Pål; Rømming, Christian; Rise, Frode; Hartshorn, Michael P.; Merchán, Manuela; Robinson, Ward T.; Roos, Björn O.; Vallance, Claire; Wood, Bryan R. (1997). "Total Synthesis of C31-Methyl Ketone Apocarotenoids 2: The First Total Synthesis of (3R)-Triophaxanthin" (PDF). Acta Chemica Scandinavica. 51: 1096–1103. doi: 10.3891/acta.chem.scand.51-1096 . Retrieved November 26, 2009.
  17. Peters, D. G.; Ji, C. (2006). "A Multistep Synthesis for an Advanced Undergraduate Organic Chemistry Laboratory". Journal of Chemical Education. 83 (2): 290. Bibcode:2006JChEd..83..290P. doi:10.1021/ed083p290.
  18. "Unit 12 Aldehydes, Ketones and Carboxylic Acids" (PDF). Chemistry Part II Textbook for class XII. Vol. 2. India: National Council of Educational Research and Training. 2010. p. 355. ISBN   978-81-7450-716-7. Archived from the original (PDF) on September 20, 2018. Retrieved March 9, 2019.
  19. Arredondo, Juan D.; Li, Hongmei; Balsells, Jaume (2012). "Preparation of t-Butyl-3-Bromo-5-Formylbenzoate Through Selective Metal-Halogen Exchange Reactions". Organic Syntheses. 89: 460. doi: 10.15227/orgsyn.089.0460 .
  20. A. Fürstner, A. Leitner, G. Seidel (2004). "4-Nonylbenzoic Acid". Organic Syntheses . 81: 33–42{{cite journal}}: CS1 maint: multiple names: authors list (link).
  21. Youhei Nobe; Kyohei Arayama; Hirokazu Urabe (2005). "Air-Assisted Addition of Grignard Reagents to Olefins. A Simple Protocol for a Three-Component Coupling Process Yielding Alcohols". J. Am. Chem. Soc. 127 (51): 18006–18007. doi:10.1021/ja055732b. PMID   16366543.
  22. Richey, Herman Glenn (2000). Grignard Reagents: New Developments. Wiley. ISBN   0471999083.
  23. Jordan VC (1993). "Fourteenth Gaddum Memorial Lecture. A current view of tamoxifen for the treatment and prevention of breast cancer". Br J Pharmacol. 110 (2): 507–17. doi:10.1111/j.1476-5381.1993.tb13840.x. PMC   2175926 . PMID   8242225.

Further reading

Specialized literature