B.J.J. van de Heisteeg

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.

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.

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%).

Die bildung von titanocen-methylen-komplexen aus 1,3-dititanacyclobutanen

The dititanacyclobutane Cp2TiCH2Ti(Cp2)CH2 (2) reacts rapidly and quantitatively with PMe3 to give the complex Cp2TiCH2 · PMe3 (1a); its structure is discussed on the basis of its NMR spectra. The reaction is found to be rather sensitive to steric and electronic factors.

1,1-Dicyclopentadienyl-3,3-dimethylvanada(IV) cyclobutane

Abstract The reaction of 1,3-bis(bromomagnesio)-2,2-dimethylpropane (1b) with dichlorodicyclopentadienylvanadium(IV) (5) gave 1,1-dicyclopentadienyl-3,3-dimethylvanada(IV)cyclobutane (4) in 30% yield, contaminated with dicyclopentadienylneopentylvanadium(III) (12). Attempts to purify 4 were only partially successful due to its limited stability (t 1 2 = 4 h at 25°C in cyclopentane). Identification of 4 is therefore based on its having sufficient thermal stability for isolation, on its reaction with bromine to give 1,3-dibromo-2,2-dimethylpropane (2b), and especially on its ESR and 1H NMR spectra. The reaction of 4 with cyclohexanone (15) gave 17 and 18 as the main products; 17 is the aldol dimer of 15, while 18 may be derived from either 4 or 12. Because methylenecyclohexane (16) is not one of the reaction products, it is concluded that 4 does not have a pronounced tendency to fragment to give a metallacarbene (20).

A versatile method for the synthesis of 1,3-metallatitanacyclobutanes

Abstract The reaction of Cp 2 TiCl 2 with two moles of CH 2 (MgBr) 2 gave Cp 2 Ti(CH 2 MgBr) 2 which with Me 2 MCl 2 (M  Si,Ge,Sn) was converted to the corresponding 1,3-metallatitanacyclobutanes.

Synthesis of metallacyclobutanes and metallacyclobutabenzenes of molybdenum and tungsten

Abstract Reactions of 1,3-bis(bromomagnesio)-2,2-dimethylpropane or 1-magnesacyclo-butabenzene with either dichloromolybdenocene or dichlorotungstenocene have given the corresponding four-membered metallacycles of both metals.

Interconversions of titanocene-methylene complexes

The Tebbe-type reagent Cp2Ti(X)CH2MgX (X = Br, Cl) (2) in diethyl ether/benzene gave, on evaporation of the solvent and solution in toluene, (3). Both compounds differ dramatically in their spectral properties and reactivities. Compound 3 reacts with ethers to give Cp2TiCH2Ti(Cp2)CH2. (4), with PMe3 to give Cp2(MeP3)TiCH2 (5) and with benzophenone to give 1,1-diphenylethene. Analogous derivatives were obtained from Cp′2TiCl2 (Cp′=MeC5H4).

The synthesis of four-membered spiro compounds of silicon and germanium: 2,2,6,6-tetramethyl-4-metallaspiro[3.3]heptanes

Summary The reaction of the 1,3-di-Grignard reagent 1,3-bis(bromomagnesio)-2,2-dimethylpropane ( 2 ) with silicon or germanium tetrachloride gave the 2,2,6,6-tetramethyl-4-metallaspiro[3.3]heptanes ( 1 ) in 15% (Si) and 48% (Ge) isolated yield, respectively. The spectroscopic properties of 1 are briefly discussed.