G. Schat

The structure of the grignard reagent : IX. The crystal structure of the dimeric ethylmagnesium bromide/diisopropyl ether complex

The structure of the dimeric ethylmagnesium bromide/diisopropyl ether complex [C2H5MgBr - O(i-C3H7)2]2 was studied with s ingle crystal X-ray diffraction techniques. Crystals are monoclinic with spacegroup P21/n and two dimers per unit cell of dimensions a 7.85(1), b 14.43(2), c 11,31(2) °A, β 100.3(1)o The structure was refined to a final R-value of 0.073. The magnesium is four coordinate; dimers are formed through bridging bromine atoms. p]This result is briefly discussed in the context of factors governing complex formation of Grignard reagents.

Synthese von 1,3-Dimetallacyclobutanen mit dem Methylen-di-Grignardreagens

Abstract An improved preparation of the methylene-di-Grignard reagent CH2(MgBr)2 (2) is described 2 is applied as a synthon for the preparation of 1,3-dimetallacyclobutanes (1) in a two step sequence. First,, two molar equivalents of 2 and one molar equivalent of a dichlorometallocene Cp2MCl2 (3) (M = Ti, Zr, Hf) are combined to form a 1,3-di-Grignard reagent Cp2M(CH2MgBr)2 (4) which with a metal dichloride L2M′Cl2 (L2M′ = Cp2Ti, Cp2Zr, Cp2Hf, Me2Si, Me2Ge, Me2Sn) gives 1. The 1H and 13C NMR spectra of 1 show interesting trends which are briefly discussed.

The coordination modes of simple diarylmagnesium species: Some representative X-ray crystal structures

The coordination modes of simple diarylmagnesium species have been investigated by crystal structure studies of representation compounds. In the case of diphenylmagnesium (1), both the solvated monomeric complex Ph2Mg·[THF]2 (1a) and the solvent-free compound [Ph2Mg]n (1b) were characterized. A polymeric structure was found for 1b, with tetrahedrally coordinated magnesium atoms interconnected by μ,η1-bridging phenyl groups to form linear chains. Bis(p-tolyl)magnesium (3) crystallized in a remarkable double structure that contained dimeric and monomeric units in a 1:2 ratio. In the dimer, two aryl groups are μ,η1-bridging.

Some applications of the methylene di-Grignard reagent for the synthesis of main group IV organometallic compounds

Abstract The di-Grignard reagent methylenedimagnesium dibromide, CH2(MgBr)2 (1), which can be prepared from dibromomethane and magnesium amalgam in diethyl ether/benzene 1/1, has been obtained in a pure form. Treatment of 1 with tetrahydrofuran gave insoluble 5″, a reagent with the approximate composition CH2Mg·CH2(MgBr)2. Both reagents were used for the synthesis of the dimetallomethanes (Me3M)2CH2 (M = Si, Ge, Sn) and (CH2(HgBr)2. Reaction of 1 or 5″ with dichlorodimethylgermane or dichlorodimethylstannane gave the polygermacycloalkanes ((Me2GeCH2)n; n = 2,3,4) or polystannacycloalkanes ((Me2SnCH2)n; n = 3,4), respectively, in useful yields (10 to 35%). In the germanium series, there is a pronounced tendency to form the smaller ring systems; in particular, the reaction of 5″ with Me2GeCl2 gave 30–35% of 1,1,3,3,-tetramethyl-1,3-digermacyclobutane. In contrast, the corresponding distannacyclobutane was not observed, but the eight-membered species (Me2MCH2)4 was formed more readily for M = Sn (9% yield) than for M = Ge (2% yield).

A general synthesis of metallacyclobutanes

Abstract Metallacycloalkanes containing four to six carbon atoms are easily synthesized from α,ω-dimetal-organic compounds and the appropriate metal dihalide. Metallacyclobutanes were not accessible in this way however, as the corresponding organometallic reagents were not easily available. However, our recent synthesis of di-Grignard reagents from 1,3-dibromopropanes allowed the development of a general synthesis of the title compounds. In addition to the synthesis in high yields of the (already known) germana- and titana-cyclobutanes, the method has also proved useful in the preparation of stanna-, hafna-, zircona- and vanada-cyclo butanes. The newly prepared compounds have been characterized by their NMR spectra (plus the ESR spectrum for the paramagnetic vanadium compound) and the products of their reaction with elemental bromine. Their behaviour as organometallic compounds has been derived from their reactions with cyclohexanone. The scope and limitations of the synthesis appear to be mainly determined by the stability of the 1,3-di-Grignard compounds, which is strongly dependent on the substitution pattern.

Bifunctional and cyclic organomagnesium compounds: III. The crystal and molecular structure of the dimer of magnesiacyclohexane, 1,7-dimagnesiacyclododecane

Summary The structure of the dimer of magnesiacyclohexane, the 1,7-dimagnesiacyclododecane/tetrahydrofuran complex [(CH 2 ) 5 Mg] 2 • 4THF (IV) has been determined by single X-ray diffraction techniques. Crystals are triclinic with space-group P 1 and one centrosymmetric dimer per unit cell of dimensions a 8.85(2), b 9.60(2), c 9.63(2)A, α 92.2(3), β 93.2(3), γ 112.7(3)°. The structure was refined to a final R -value of 0.094. Dimer IV contains two tetracoordinated magnesium atoms in a twelve-membered ring. The conformation of IV is discussed in the context of other medium-sized ring structures. The strong tendency to form a twelve-membered ring is ascribed to the remarkably large C Mg C valence angle of 141.5°, which causes ring strain in monomeric magnesiacyclohexane and thus makes dimerization exothermic (Δ H = −11.5 ± 0.8 kcal mol −1 , Δ S = −25 ± 3 eu). The unfavourable entropy of association explains the absence of higher polymers in solutions.

Complexation of diphenylzinc with simple ethers. Crystal structures of the complexes Ph2Zn · glyme and Ph2Zn · diglyme

Abstract The complexation behavior of diphenylzinc with a series of mono-, di- and tri-coordinating ethers has been investigated. Two stable crystalline 1 : 1 adducts, with ethyleneglycol dimethyl ether (glyme) ( 1 ) and diethyleneglycol dimethyl ether (diglyme) ( 2 ) were isolated and characterized by an X-ray diffraction study. Complex 1 has a normal tetra-coordinated zinc atom; 2 represents the first example of a complex penta-coordinated diorganozinc compound, and has a rather unusual geometry.

Methylenedimagnesium dibromide as precursor of metal carbene complexes; preparation of titanacyclobutanes.

Abstract The reaction of CH 2 (MgBr) 2 with Cp 2 TiCl 2 gives a titanium methylene complex which, similar to Tebbes reagent, forms four-membered titana-heterocycles with alkenes and alkines.

The structure of 1,4-bisorganomagnesium compounds in magnesacyclopentane

1,4-Bis(bromomagnesio)butane (VI) and magnesacyclopentane (IV) were prepared and investigated as such and in combination with MgBr2 by measuring the degree of association in THF solution at three temperatures. It was established that IV does not exist as such, but is completely dimerized to 1.6-dimagnesacyclodecane (V). A Schlenk equilibrium is established between V and VI with K{in4}(28.17∘) = 100 ± 50, K{in4}(39.75∘) = 250 ± 100 and K{in4}(48.84∘) = 500 ± 200 and the thermodynamic parameters ΔH{in4} = 15 kcal mol-1 and ΔS{in4} = 59 e.u. These values are very close to those of the higher homologue, 1,5-bis(bromomagnesio)pentane (III) and of ethylmagnesium bromide. It is concluded that these di-Grignard reagents behave essentially like the normal monovalent Grignard reagents.

Bis(bromomagnesio)trimethylsilylmethane

Abstract The reaction of Me 3 SiCHBr 2 with magnesium amalgam in diisopropyl ether furnished the di-Grignard reagent Me 3 SiCH(MgBr) 2 in 70% yield. Derivatization with Me 3 SnCl gave Me 3 SiCH(SnMe 3 ) 2 (6,94%). Wittig type reaction occurred readily with benzophenone (80%), but the yield was low with cyclohexanone (13%).