The Composition of Grignard Reagents as Determined by Precipitation with Dioxane

Noller, C. R.; White, W. R.

doi:10.1021/ja01286a055

Cited by 23 publications

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“…Conducting the iron-catalyzed hydromagnesiation of styrene in d 8 -tetrahydrofuran gave a mixture of (1-phenylethyl)magnesium bromide ( 2 ; RMgBr) and bis(1-phenylethyl)magnesium ( 3 ; R 2 Mg), which could be observed at room temperature (25 °C) in a ratio of 1:1.5, corresponding to an equilibrium constant ( K eq ) of 0.44 (Scheme ). , Characterization was aided by perturbation of the Schlenk equilibrium to favor either organomagnesium species. Addition of 1,4-dioxane resulted in the precipitation of MgBr 2 ·(dioxane) to give a majority of 3 , while addition of MgBr 2 led to an increase in 2 (Figure ). Two-dimensional NMR spectroscopy was used to identify and fully characterize 2 and 3 .…”

Section: Resultsmentioning

confidence: 99%

Iron-Catalyzed Hydromagnesiation: Synthesis and Characterization of Benzylic Grignard Reagent Intermediate and Application in the Synthesis of Ibuprofen

et al. 2014

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Iron-catalyzed hydromagnesiation of styrene derivatives using ethylmagnesium bromide has been investigated for the synthesis of benzylic Grignard reagents. The benzylic Grignard reagent formed in the reaction was observed directly and its conformation in solution characterized by multinuclear and variable-temperature NMR spectroscopy. The Grignard reagent could be stored for at least 2 weeks without significant loss in activity. Hydromagnesiation of styrene in tetrahydrofuran gave a mixture of monoalkyl-and dialkylmagnesium species, (1phenylethyl)magnesium bromide (2; RMgBr) and bis(1-phenylethyl)magnesium (3; R 2 Mg), with the equilibrium between these species lying in favor of the dialkylmagnesium species. The thermodynamic parameters of alkyl exchange for the reaction MgBr 2 + R 2 Mg (3) ⇌ 2RMgBr (2) were quantified, with the enthalpy and entropy of formation of 2 from MgBr 2 and 3 calculated as 32 ± 7 and 0.10 ± 0.03 kJ mol −1 , respectively. This methodology was applied, on a 10 mmol scale, as the key step in the synthesis of ibuprofen, using sequential iron-catalyzed alkyl−aryl and aryl−vinyl cross-coupling reactions to give 4isobutylstyrene, which following hydromagnesiation and reaction with CO 2 gave ibuprofen. Each step proceeded in excellent yield, at temperatures between 0 °C and room temperature, at atmospheric pressure. Inexpensive, nontoxic, and air-and moisture-stable iron(III) acetylacetonate was used as the precatalyst in each step in combination with inexpensive amine ligands.

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Section: Resultsmentioning

confidence: 99%

Iron-Catalyzed Hydromagnesiation: Synthesis and Characterization of Benzylic Grignard Reagent Intermediate and Application in the Synthesis of Ibuprofen

et al. 2014

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“…The effect of different R groups and of the halide substituents on the Schlenk equilibrium was further investigated by Schlenk, Jr. and other groups. , It was found that the addition of dioxane to solutions of Grignard reagents not only led to precipitation of MgX 2 and RMgX as their dioxane adducts but also could shift the equilibrium to the right. , This offered a simple and general approach to the preparation of halide-free diorganomagnesium compounds. Furthermore, the solvent and temperature dependence of the Schlenk equilibrium in the presence of dioxane was studied .…”

Section: Introductionmentioning

confidence: 99%

1,4-Dioxane Adducts of Grignard Reagents: Synthesis, Ether Fragmentation Reactions, and Structural Diversity of Grignard Reagent/1,4-Dioxane Complexes

et al. 2009

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The 1,4-dioxane precipitation method was employed to obtain solutions of R 2 Mg from Grignard reagents via precipitation of polymeric magnesium dihalides as dioxane adducts. The addition of a slight excess of dioxane resulted in partial cleavage of the initially formed [( μ-diox)MgR 2 ] ¥ polymer into smaller fragments of the type [(diox) nþ1 (MgR 2 ) n ]. In addition to the polymeric compounds(2) can be obtained from such solutions. In the system MesMgBr/1,4dioxane the compounds [( μ-diox)MgBr 2 ] ¥ and [( μ-diox)Mg(Mes) 2 ] ¥ are both sparingly soluble, offering the opportunity to remove most of these compounds from the reaction mixture and leaving the products of ether cleavage reactions as the major species in solution. Using this procedure, the new ether degradation products [(diox)Mg(Mes)(μ-OEt)] 2 (3) and [(EtOCH(Me)CH(Me)OEt)Mg-(Mes) 2 ] (4) were isolated. Excess dioxane yields mononuclear [(diox) 2 Mg(Mes) 2 ] (5). Exchange of the thf coligands in closely related [(thf) 2 Mg(Mes) 2 ] for other Lewis bases such as 2,2 0 -bipyridine (bpy) and 2,4,6-trimethylphenyl (Mes) anions allowed the preparation of [(bpy)Mg(Mes) 2 ] (6) and [(thf) 4 -Li] þ [Mg(Mes) 3 ] -(7). Molecular structures of all new compounds 2-7 are reported.

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“…Dialkylmagnesium is often obtained by displacement of the Schlenk equilibrium of the corresponding alkylmagnesium bromide in ethereal solution. − In a first step, 1-(3-bromopropyl)-2,2,5,5-tetramethyl-1-aza-2,5-disilacylopentane ( 1 ) (Scheme ) was isolated by reacting 1,1,4,4-tetramethyl-1,4-dichloro-1,4-disilabutane with 3-bromopropylamine hydrobromide (see Supporting Information Figure S1). Di(1-(propyl)-2,2,5,5-tetramethyl-1-aza-2,5-disilacylopentane)magnesium ( 3 ) was further successfully obtained by addition of 1.5 equiv of dioxane to a THF solution of 1-(propyl)-2,2,5,5-tetramethyl-1-aza-2,5-disilacylopentane magnesium bromide ( 2 ) obtained from 1 .…”

Section: Resultsmentioning

confidence: 99%

Amino End-Functionalized Polyethylenes and Corresponding Telechelics by Coordinative Chain Transfer Polymerization

et al. 2017

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Di(1-(propyl)-2,2,5,5-tetramethyl-1-aza-2,5-disilacylopentane)magnesium was synthesized and used as chain transfer agent for the ethylene polymerization in the presence of a neodymocene precursor. The polymerization was shown to be governed by a catalyzed chain growth process (CCG) on magnesium, allowing the quantitative formation of ammonium or amine functionalized polyethylene (PE) chains. The structure of these chains was shown by 1H and 13C NMR analyses. MALDI-ToF mass spectrometry was successfully used to confirm the structure predicted by the CCG mechanism. The additional formation of telechelic PE chains carrying an ammonium and either a diethyldithiocarbamate or an iodo moiety as end groups was shown after a simple deactivation of the polymerization medium with disulfiram or molecular iodine, respectively.

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The Composition of Grignard Reagents as Determined by Precipitation with Dioxane

Abstract: The salt was dehydrated completely at 78°over phosphorus pentoxide. A sample of the salt weighing 25.270 ing. dried at room temperature over phosphorus pentoxide when completely dehydrated at 78°lost 0.378 mg. weight, or 1.50%. This dehydrated salt was analyzed for nitrogen.

Cited by 23 publications

References 0 publications

Iron-Catalyzed Hydromagnesiation: Synthesis and Characterization of Benzylic Grignard Reagent Intermediate and Application in the Synthesis of Ibuprofen

Iron-Catalyzed Hydromagnesiation: Synthesis and Characterization of Benzylic Grignard Reagent Intermediate and Application in the Synthesis of Ibuprofen

1,4-Dioxane Adducts of Grignard Reagents: Synthesis, Ether Fragmentation Reactions, and Structural Diversity of Grignard Reagent/1,4-Dioxane Complexes

Amino End-Functionalized Polyethylenes and Corresponding Telechelics by Coordinative Chain Transfer Polymerization

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