Organomagnesium Research Articles

Zirconocene catalysis in the synthesis of 1,4-dimagnesium reagents: using competitive inhibition to suppress β-hydrogen abstraction

Substituted 1,4-dimagnesium reagents were synthesized by the zirconocene-catalyzed reaction of alkenes with ethylmagnesium reagents in the presence of a methylmagnesium containing additive. Improved selectivity for formation of dimagnesium reagents over monomagnesium reagents was obtained in the presence of the methylmagnesium containing additive. The ratio of mono- to dimagnesiated products was extrapolated from the ratio of alkene to diene in the products formed when the reaction was quenched with allyl bromide. The extent of the increase in the alkene/diene ratio was dependent on the type of organomagnesium halide, with greatest increases (59%) for the alkylmagnesium chlorides. A mechanism for improved selectivity by suppression of β-hydrogen abstraction in the catalytic cycle is presented. Quenching the 1,4-dimagnesium reagents with allyl bromide yielded decadienes.

Zirconium-mediated cyclomagnesiation of styrene using magnesacyclopentane and 1,4-di(brommagnesium)butane as a method for the preparation of macrocyclic organomagnesium compounds

Cyclometalation of styrene with 1,4-bis(brommagnesium)butane and magnesacyclopentane in the presence of Cp 2ZrCl 2 gives rise to the formation of magnesacycloalkanes, composed of one ethylene molecule and two, three or four styrene molecules.

Selective cyclometalation of disubstituted acetylenes and ethylene with diethylmagnesium and ethylmagnesium halides in the presence of zirconium complexes

Catalytic cyclometalation of disubstituted acetylenes and ethylene with ethylmagnesium halides EtMgHlg (Hlg = Cl, Br) and diethylmagnesium Et2Mg in the presence of Cp2ZrCl2 gave tetrasubstituted magnesacyclopenta-2,4-dienes and disubstituted magnesacyclopent-2-enes. A probable scheme of formation of cyclic unsaturated organomagnesium compounds was proposed, according to which the reactive intermediates in the cyclometalation process are zirconacyclopentadienes and zirconacyclopentenes generated from Cp2ZrCl2, EtMgHlg, Et2Mg, acetylenes, and ethylene.

Experimental determination of magnesium isotope fractionation during higher plant growth

Two higher plant species (rye grass and clover) were cultivated under laboratory conditions on two substrates (solution, phlogopite) in order to constrain the corresponding Mg isotope fractionations during plant growth and Mg uptake. We show that bulk plants are systematically enriched in heavy isotopes relative to their nutrient source. The Δ 26Mg plant-source range from 0.72‰ to 0.26‰ for rye grass and from 1.05‰ to 0.41‰ for clover. Plants grown on phlogopite display Mg isotope signatures (relative to the Mg source) ∼0.3‰ lower than hydroponic plants. For a given substrate, rye grass display lower δ 26Mg (by ∼0.3‰) relative to clover. Magnesium desorbed from rye grass roots display a δ 26Mg greater than the nutrient solution. Adsorption experiments on dead and living rye grass roots also indicate a significant enrichment in heavy isotopes of the Mg adsorbed on the root surface. Our results indicate that the key processes responsible for heavy isotope enrichment in plants are located at the root level. Both species also exhibit an enrichment in light isotopes from roots to shoots (Δ 26Mg leaf-root = −0.65‰ and −0.34‰ for rye grass and clover grown on phlogopite respectively, and Δ 26Mg leaf-root of −0.06‰ and −0.22‰ for the same species grown hydroponically). This heavy isotope depletion in leaves can be explained by biological processes that affect leaves and roots differently: (1) organo–Mg complex (including chlorophyll) formation, and (2) Mg transport within plant. For both species, a positive correlation between δ 26Mg and K/Mg was observed among the various organs. This correlation is consistent with the link between K and Mg internal cycles, as well as with formation of organo–magnesium compounds associated with enrichment in heavy isotopes. Considering our results together with the published range for δ 26Mg of natural plants and rivers, we estimate that a significant change in continental vegetation would induce a change of the mean river δ 26Mg that is comparable to analytical uncertainties.

N-Heterocyclic carbene stabilized adducts of alkyl magnesium amide, bisalkyl magnesium and Grignard reagents: trapping oligomeric organo s-block fragments with NHCs

Developing N-heterocyclic carbene (NHC) chemistry of simple organomagnesium compounds, this study reports the synthesis, X-ray crystallographic, and NMR spectroscopic characterization of three such new carbene complexes. The 1 : 1 alkyl magnesium amide : carbene complexes nBuMg(TMP)·IPr 1 and nBuMg(HMDS)·IPr 2 both exist as mononuclear complexes in the crystal but differ in solution as 2 remains intact whereas 1 undergoes a dynamic exchange involving partial decoordination of IPr [TMP is 2,2,6,6-tetramethylpiperidide; IPr is 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene); HMDS is 1,1,1,3,3,3-hexamethyldisilazide]. Reaction of commercial nBu(2)Mg with IPr surprisingly produced the organoaluminium carbene complex nBu(3)Al·IPr, 3, which also forms a simple mononuclear structure in the crystal. The presence of the Al could be traced to the deliberate addition of a small quantity of Et(3)Al as a stabilizing agent in the commercial nBu(2)Mg reagent. Repeating this reaction with Al-free nBu(2)Mg afforded the hemisolvated carbene complex nBu(8)Mg(4)·2IPr, 4, the stoichiometry of which is dictated by its structure rather than by that used in the initial reaction mixture. The molecular structure of 4 is tetranuclear with a linear chain of 4 Mg centres bridged by nBu ligands and capped at each end by terminal nBu and IPr ligands. Synthesized by treating the Grignard reagent nBuMgCl with IPr, nBuMgCl·IPr, 5, forms a cyclodimer structure with chloro bridges and terminal nBu and IPr ligands.

Cyclomagnesation of cycloalkynes with the use of RMgR’ catalyzed by zirconium complexes

The intermolecular cyclomagnesation of cycloalkynes and joint cyclomagnesation of cycloalkynes and disubstituted acetylenes was carried out by treating with RMgR′ (R, R′ = Et, Bu, Hlg) in the presence of Cp2ZrCl2 as a catalyst. As a result new unsaturated bi-and tricyclic organomagnesium compounds were obtained in high yields.

Book Review of The Chemistry of Organomagnesium Compounds, Parts 1−2: R−Mg

Book Review of The Chemistry of Organomagnesium Compounds, Parts 1−2: R−Mg

Novel Mg-organic reagents in organic synthesis. Cp 2TiCl 2 catalyzed intermolecular cyclomagnesiation of cyclic and acyclic 1,2-dienes using Grignard reagents

High-yield (>80%) catalytic intermolecular cyclomagnesiation of cyclic and acyclic allenes with the aid of Grignard reagents has been realized in the presence of Cp 2TiCl 2. The synthesized unsaturated bi- and tricyclic organomagnesium compounds (OMC) have been successfully converted in situ into thiophenes, unsaturated ketones, cyclic and acyclic hydrocarbons with high regio- and stereoselectivity.

Reaction of 4-aryl-2,6-dichlorobenzo[e[1,2]oxaphosphinine 2-oxides with organomagnesium compounds as a convenient synthetic approach to (Z)-dialkyl(aryl)[2-(2-hydroxyaryl)-2-arylethenyl]phosphine oxides

We recently prepared benzo[e][1,2]oxaphosphinine 2-oxides [1, 2], phosphorus analogs of coumarins which are widespread in nature and possess diverse biological activity [3]. The chemical behavior of this class of compounds is comparatively poorly studied. Thus it was shown that they fairly readily chlorinated [4] and brominated [5] into the heterocyclic fragment to form finally 3-halo derivatives. In the present work we investigated for the first time reactions of 4-aryl2,6-dichlorobenzo[e][1,2]oxaphosphinine 2-oxides I with organomagnesium reagents (Grignard reagents). Taking into account the data summarized in the monograph [6], we expected that the reactions would lead to 2-alkyl(aryl)-4-aryl-6-chlorobenzo[e][1,2]oxaphosphinine 2-oxides II which attract some interest as complexing agents for rare metals. However, phosphinines I were found to react unambiguously with a double excess of Grignard reagents to give functionally substituted phosphine oxides III in quantitative yields. At an equimolar ratio of the starting reagents, mixtures of phosphinines II, phosphine oxides III, and 2-hydroxy-4-aryl-6-chlorobenzo[e][1,2]oxaphosphinine 2-oxides IV formed. It is obvious that Grignard reagents almost equally reactive toward DOI: 10.1134/S1070363208060340

Rate and equilibrium constants for Grignard reaction with alkoxysilanes and ketones

Kinetics of tetraethoxysilane reaction with n-butylmagnesium chloride, specifically solvated with dibutyl ether, diethyl ether, THF, and triethylamine, was studied in toluene. Also isopropylmagnesium chloride, isopropyltriethoxysilane, and diisopropylketone were involved in a similar investigation. The pseudo-first-order rate constants determined at a great excess of these organomagnesium compounds were used for separation of the appropriate equilibrium and rate constants. An advantage of the method consists in preclusion of non-specific solvation effects when effects of donor solvents are considered. In separate experiments, thermodynamic parameters were determined for rate and equilibrium constants, measured for the reaction of tetraethoxysilane with n-butylmagnesium chloride solvated with dibutyl ether in toluene, and also in bulk dibutyl ether. The implication of steric and solvation effects on this reaction is discussed.

Preferred Functionalization of Metallic and Small‐Diameter Single‐Walled Carbon Nanotubes by Nucleophilic Addition of Organolithium and ‐Magnesium Compounds Followed by Reoxidation

Covalent sidewall addition to single-walled nanotubes (SWNTs) of a series of organolithium and organomagnesium compounds (nBuLi, tBuLi, EtLi, nHexLi, nBuMgCl, tBuMgCl) followed by reoxidation is reported. The functionalized R(n)-SWNTs were characterized by Raman and NIR emission spectroscopy. The reaction of SWNTs with organolithium and magnesium compounds exhibits pronounced selectivity: in general, metallic tubes are more reactive than semiconducting ones. The reactivity of SWNTs toward the addition of organometallic compounds is inversely proportional to the diameter of the tubes. This was determined simultaneously and independently for both metallic and semiconducting SWNTs. The reactivity also depends on the steric demands of the addend. Binding of the bulky t-butyl addend is less favorable than addition of primary alkyl groups. Significantly, although tBuLi is less reactive than, for example, nBuLi, it is less selective toward the preferred reaction with metallic tubes. This unexpected behavior is explained by fast electron transfer to the metallic SWNTs having low-lying electronic states close to the Fermi level, a competitive initial process. The NIR emission of weakly functionalized semiconducting SWNTs, also reported for the first time, implies interesting applications of functionalized tubes as novel fluorescent reporter molecules.

Exploration of meso‐Substituted Formylporphyrins and Their Grignard and Wittig Reactions

AbstractFormylporphyrins were prepared by using either the 1,3‐dithian‐2‐yl residue as a precursor for the CHO group or by the Vilsmeier reaction. Two synthetic routes for the introduction of the 1,2‐dithian‐2‐yl group were explored. Furthermore, reactions of the 1,3,5‐trithian‐2‐yl group with porphyrins were examined as well as spirobisdithiane derivatives as precursors for the ultimate assembly of porphyrin spirobisdithanyl‐linked bioconjugates. The obtained formylporphyrins were reacted with organomagnesium or organophosphorus compounds. A series of hydroxyporphyrins resulting from the Grignard reaction of 5,15‐substituted porphyrins were synthesised in high yields. Several porphyrins with unsaturated residues introduced by the Wittig reaction were obtained in moderate yields. The less sterically hindered 5,15‐substituted porphyrins show increased reactivity and give higher yields; their reaction products are higher in stability relative to other porphyrin systems.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

First example of one-pot synthesis of hydrocarbon macrorings

Cyclomagnesation of α,ω-diallenes by EtMgBr in the presence of chemically activated Mg and Cp2TiCl2 catalyst led to the formation of cyclic organomagnesium compounds whose hydrolysis provided gigantic hydrocarbon macrorings with 1,5-cis-disubstituted double bonds.

Interaction of (1‐Phenylethyl)indole‐2‐carbonitrile with C‐Nucleophiles.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Mechanistic Studies of the Copper-Catalyzed Electrophilic Amination of Diorganozinc Reagents and Development of a Zinc-Free Protocol

[reaction: see text] An SN2 mechanism for the copper-catalyzed amination of diorganozinc reagents by O-benzoyl-N,N-dialkylhydroxylamines is supported by following stereochemically defined organometallics through the reaction and by employing the endocyclic restriction test. A copper-catalyzed electrophilic amination of organomagnesium compounds is also described in which the use of zinc halides has been eliminated.

Preparation of Substituted Hydroquinones and Benzofurans from 1,4‐Quinone Monoketals.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Organolithium and Organomagnesium Compounds of the Naphthalene Series in Organic Synthesis

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Cobalt-Catalyzed Cross-Coupling Reactions of Heterocyclic Chlorides with Arylmagnesium Halides and of Polyfunctionalized Arylcopper Reagents with Aryl Bromides, Chlorides, Fluorides and Tosylates

A range of aromatic organocopper or organomagnesium compounds undergo smooth cross-coupling reactions with aryl bromides, chlorides, fluorides and tosylates, leading to polyfunctionalized aromatics or heterocycles in the presence of cobalt salts (5-7.5 mol%) as catalysts. Very mild reaction conditions are needed and, in the case of cross-coupling with organocopper compounds, BU 4 NI (1 equiv) and 4-fluorostyrene (20 mol%) are essential as promoters for successful couplings.

Preparation of Substituted Hydroquinones and Benzofurans from 1,4-Quinone Monoketals

An easy procedure for the preparation of 2-substituted hydroquinones, by addition of organolithium or organomagnesium compounds to 1,4-quinone monoketals followed by acid-catalyzed dienone-phenol type rearrangement, is described. Transformation of the propargylated derivatives to benzofurans is also reported.

Interaction of (1-phenylethyl)indole-2-carbonitrile with C-nucleophiles

Methods of obtaining ketones and enamino esters have been developed on the basis of reactions of 1-(1-phenylethyl)indole-2-carbonitrile with organomagnesium and organozinc compounds. Removal of a benzyl group from the indole nitrogen atom by the Grignard reagent has been discovered.