Isopropylmagnesium chloride
Chemical compound
From Wikipedia, the free encyclopedia
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.
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| ChemSpider | |
| ECHA InfoCard | 100.012.680 |
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CompTox Dashboard (EPA) |
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| Properties | |
| C3H7ClMg | |
| Molar mass | 102.84 g·mol−1 |
| Solubility | Ethyl ether |
| Hazards | |
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| Danger | |
| H225, H260, H314 | |
| P210, P223, P231+P232, P233, P240, P241, P242, P243, P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P335+P334, P363, P370+P378, P402+P404, P403+P235, P405, P501 | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Synthesis and reactivity
Solutions of isopropylmagnesium chloride by treating isopropyl chloride with magnesium metal in refluxing ether:[1]
- (CH3)2HCCl + Mg → (CH3)2HCMgCl
This reagent is used to prepare other Grignard reagents by transmetalation.[2] An illustrative reaction involves the generation of the Grignard reagent derived from bromo-3,5-bis(trifluoromethyl)benzene:[3]
- (CH3)2HCMgCl + (CF3)2C6H3Br → (CH3)2HCCl + (CF3)2C6H3MgBr
Addition of one equivalent of LiCl to isopropylmagnesium chloride gives "Turbo Grignard" solutions, named so due to the increased rate and efficiency for transmetalation reactions.[4][5]
Isopropylmagnesium chloride is also used to prepare isopropyl compounds, such as chlorodiisopropylphosphine:[6]
- PCl3 + 2 (CH3)2CHMgCl → [(CH3)2CH]2PCl + 2 MgCl2
This reaction exploits the bulky nature of the isopropyl substituent.
Turbo-Grignard reagents
As initially reported by Knochel et al.,[7] lithium chloride enhances the ability of isopropylmagnesium chloride toward transmetalation reactions. The more reactive species, a LiCl-iPrMgCl complex, is called a Turbo-Grignard reagent. These species are related to Turbo-Hauser bases, a family of magnesium amido compounds containing also LiCl.[8] "Turbo-Grignards", as they are often called, are aggregates with the formula [i-PrMgCl·LiCl]2. These species promote formation of aryl and heteroaryl Grignard reagents by halogen-magnesium exchange:[9]
- fast, homogeneous: XC6H4Br + i−PrMgCl·LiCl → XC6H4MgCl·LiCl + i−PrBr
The traditional method for generating the aryl Grignard reagent proceeds less predictably:
- slow, heterogeneous: XC6H4Br + Mg → XC6H4MgBr
Furthermore, traditional routes to Grignard reagents has limited functional group compatibility, whereas the Turbo-Grignard method tolerates other halides, some ester groups, and nitriles.
Studies suggest that the enhanced reactivity towards electrophiles by "Turbo-Grignard" reagents in comparison to their "classic" equivalent can be attributed to a greater concentration of nucleophilic magnesate complexes in the solution due to the presence of LiCl.[10][11]
Structure and speciation
In ether solution, chloride-containing Grignard reagents consist of ether complexes, often as clusters such as R2Mg4Cl6(THF)6.[12] In the case of the Turbo Grignard reagent, the cluster R2Mg4Cl6(THF)6 was identified by X-ray crystallography.[13]