Investigations on the Reactivity of Bis(bromomagnesio)trimethylsilylmethane − Molecular Structure of a Tebbe‐Type Spiro‐Organomagnesium Compound

Abstract

The reactivity of the 1,1‐di‐Grignard reagent Me3SiCH(MgBr)2 (8) towards transition metal dihalides has been investigated. While most transformations were sluggish and gave no well‐defined products, the reaction of 8 with [Cp2ZrCl2] in a 1:1 ratio gave, in low yield, the novel spiro‐organomagnesium compound [Cp2ZrCHSiMe3(μ‐Br)]2Mg (12), which is stable at room temperature and does not disproportionate on addition of dioxane. An X‐ray crystal structure determination has shown that, in the solid state, 12 is present as the C2 symmetric stereoisomer 12a; it is sterically very crowded due to the trimethylsilyl substituents. Partial metalla‐alkene character is indicated by the short zirconium−carbon bonds, and agostic zirconium−hydrogen interactions by the short zirconium−hydrogen distances (Zr···H−C) and small 1JC,H coupling constants. In benzene solution, equilibrium between 12a and its C1 symmetric stereoisomer 12b was detected by 1H and 13C NMR spectroscopy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

2 Alkali and alkaline-earth metals

“…80 Most reactions of the 1,1-di-Grignard reagent, Me 3 SiCH(MgBr) 2 , with transition metal halides gave no well-defined products but Cp 2 ZrCl 2 afforded the spiro compound [Mg{Cp 2 ZrCHSiMe 3 (m-Br)} 2 ]. 81 The carbenoid homologation of a-haloalkyl Grignard reagents with Mg(Pr i )Cl gives not only the expected secondary compounds but also the tertiary species, possibly via C-H insertion within the mixed halide-bridged intermediate. 82 The preparation of some Grignard clusters, [Mg 4 (Ph)X] (X = Cl or Br), in solution 83 and the preparations and X-ray structures of [Mg(m-Br){CH(SiMe 3 ) 2 }(OEt 2 )] 2 and [Mg{CH(SiMe 3 ) 2 } 2 (OEt 2 )] have been reported.…”