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Trimethylsilylmethylcalcium Iodide, an Easily Accessible Grignard-Type Reagent of a Heavy Alkaline Earth Metal

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posted on 25.01.2016, 00:00 authored by Mathias Köhler, Alexander Koch, Helmar Görls, Matthias Westerhausen
The direct synthesis of iodomethyl­trimethylsilane with calcium and magnesium in ether yields the corresponding ether adducts [(thf)4Ca­(I)­(CH2SiMe3)] (1a) and [(Et2O)2Mg­(I)­(CH2SiMe3)] (2a). The 1,4-dioxane method allows shifting the Schlenk equilibrium toward bis­(trimethylsilylmethyl)­magnesium 2b. After substitution of ligated thf ligands by tetrahydropyran (thp) crystalline [(thp)4Ca­(I)­(CH2SiMe3)] (1b) can be isolated. The Ca–C and Ca–I bond lengths of 252.7(3) and 319.11(3) pm represent characteristic values. Steric repulsion between ligated thp ligands and the rather bulky trimethylsilylmethyl group widens the Ca–C–Si angle to 131.19(14)°. NMR data and quantum chemical studies support that hyperconjugative effects might be operative, leading to a shortened Si–C bond of this Ca–C–Si fragment.