Organomagnesium halide,

Holm determined the enthalpies of formation of a collection of hydrocarbyhnagnesium bromides by reaction calorimetry with HBr in diethyl ether . He also determined the enthalpies of formation in ethereal solution of the magnesium bromide salts of 20 Bronsted acids, HB, by measuring the enthalpies of reaction of the acid with pentylmag-nesium bromide. For those species that were reported in both studies (hydrocarbyl = phenylethynyl, phenyl, methyl, cyclopropyl, cyclopentyl, cyclohexyl), the enthalpies of formation were identical. The values are listed in Tables 3 and 4. 

There is one other report in the literature of a measurement of the enthalpy of formation of an organomagnesium halide. The enthalpy of reaction of magnesium with methyl iodide in ether was calorimetrically determined as —273.6 0.8 kJmoH Using a recent enthalpy of formation for liquid methyl iodide of —13.6 0.5 kJmoU, the enthalpy of formation of methylmagnesium iodide is —287.2 kJmoU. The exchange (equation 8) is thus 11.2 kJmoU endothermic. 

TABLE 3. Enthalpies of reaction and enthalpies of formation of hydrocarbyhnag-nesium hromides (RMgBr) in ether solution (kJ mol ) 

There is one additional study on the enthalpy of hydrolysis of solid butylmagnesium chloride. Additional calculations result in a solid phase enthalpy of formation of -455.7 2.0 kJmol-.  

---

The much simpler steroid, 253, was fortuitously found to fulfill this role when injected into animals. Its lack of oral activity was overcome by incorporation of the 7a-thioacetate group. Reaction of the ethisterone intermediate, 77b, with a large excess of an organomagnesium halide leads to the corresponding acetylide salt carbonation with CO2 affords the carboxyllic acid, 251. This is then hydrogenated and the hydroxy acid cy-clized to the spirolactone. Oppenauer oxidation followed by treatment with chloranil affords the 4,6-dehydro-3-ketone (254). Conjugate addition of thiolacetic acid completes the synthesis of spironolactone (255), an orally active aldosterone antagonist. ... 

The reduction of carbonyl compounds by reaction with hydride reagents (H -) and the Grignard addition by reaction with organomagnesium halides (R - +MgBr) are examples of nucleophilic carbonyl addition reactions. What analogous product do you think might result from reaction of cyanide ion with a ketone ... 

Grignard reagent (Section 10.7) An organomagnesium halide, RMgX. 

As precursors of the organocopper compounds, organolithium reagents are slightly preferable to organomagnesium halides. 

Allenyl and 1- and 2-alkynyl sulfoxides have also been prepared by reaction of organomagnesium halides with sulfinate ester 19. 1-Alkynyl p-tolyl sulfoxides were prepared in good yield from 1-alkynylmagnesium halides plus ester 19 in toluene (equation ll)63. The corresponding organolithium compound was unsatisfactory as a... 

Organomagnesium halide reagents RMgX (RX = CjH,Br, i-PrBr, n-BuBr, PhBr) react in toluene-ether with (t7 -Cp)2MoH2 to form compounds II, in which each molecule contains four Mo—Mg bonds " . When II is dissolved in THF a red solution is formed, which after concentration yields orange crystals of III. Compound III is monomeric with a Mo—Mg bond of length 273.2 pm, consistent for Mo as a one-electron donor. 

Organomagnesium halides were discovered by the French chemist Victor Grignard in 1900. 

Grignard received the Nobel Prize in 1912 and organomagnesium halides are now called Grignard reagents. 

Organolithium compounds, 2 69 ring stacking, 37 82-92 systems capable of, 37 82-83 uncomplexed, structure, 37 53-54 X-ray crystal structure, 37 48 Organomagnesium halides, 2 71 Organomercury compounds, see Mercury, -carbon compounds Organometallic complexes... 

The second route (Scheme 1) is a redistribution reaction, in fact the Schlenk equilibrium. This route may be used in the reverse direction for the preparation of pure diorganomagnesium compounds from organomagnesium halides. Addition of a ligand, usually dioxane, that forms an insoluble complex with magnesium dihalide, shifts the Schlenk equilibrium completely to the left side and allows isolation of pure diorganomagnesium compounds from the remaining solution. ... 

The dimeric organomagnesium halide complexes 187-189 (Figure 82) were obtained from the reaction of (2-Py)(SiMe3)2C-Sb=C(SiMe3)(2-Py) with Et2Mg in THF in the... 

FIGURE 82. Schematic structures of organomagnesium halides containing monoanionic C,N-chelating hgands... 

Bromo- and iodoanihnes, -phenols and -benzoic acids are first deprotonated in situ by an excess of the organomagnesinm reagent and then coupled (PdCl2(dppf), 1 mol%, THF, 25 °C, 3 h) with organomagnesium halides, thus avoiding tedious protection-deprotection steps . Iron(in) salts can also serve as appropriate catalysts for varions cross-coupling... 

O-Benzyllactaldehyde dimethylhydrazone 230 allows a substrate control in the addition reaction of organomagnesium halides, leading almost exclusively to the 5yn-isomer 231 (equation 155) . The resulting hydrazide can be reduced on Raney Ni to the corresponding iyw-aminoalcohol 232. The stereoselective Grignard addition to a similar A-formyl hydrazone 233 proceeds with 92% diastereoselectivity (equation 156). The silylation of the amide nitrogen by TMSCl provides the pure iyw-adduct . 

The term Grignard reaction refers to both the preparation of a class of organomagnesium halide compounds and their subsequent reaction with a wide variety of organic and inorganic substrates. As such it has had a wide and profound influence on synthetic chemistry since its first elucidation by Victor Grignard at the beginning of the twentieth century. 

The stability of the alkyl and aryl derivatives increases with the number of phosphines bound to nickel(II). The bis-phosphine derivatives can be prepared according to equations (144)-(146) and using organomagnesium halides or organolithium compounds.1224-1231 A tetrakis phosphine complex was obtained similarly (equation 147). 

---