Some sterically hindered lithium alkylbromo- and alkylchloro-magnesates, -cadmates, and -manganates. Crystal and molecular structures of [Li(thf)2(µ-Br)2Mg{C(SiMe3)3}(thf)], [Li(thf)4][{Cd[C(SiMe3)3]}3(µ-Br)3(µ3-Br)]·0.5C6H12, [{Li(thf)}3(µ3-Br)3(µ3-OSiMe3)Cd{C(SiMe3)3}], and [Li(thf)4][{Mn[C(SiMe3)3]}3(µ-Cl)4(thf)](thf = tetrahydrofuran)

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Abstract
Tris(trimethylsilyl)methyl-lithium reacts with anhydrous magnesium(II) bromide to give the magnesate [Li(thf)2(µ-Br)2Mg{C(SiMe3)3}(thf)](1), which has been shown by an X-ray study to have a structure with two bridging bromine atoms between lithium and magnesium. With cadmium(II) bromide, Li{C(SiMe3)3} gives the tricadmate [Li(thf)4][{Cd[C(SiMe3)3]}3(µ-Br)3(µ3-Br)]·0.5C6H12(2)(C6H12= cyclohexane), in which the anion has a structure based on a Cd3Br4 cube with one corner missing. In the presence of traces of moisture, the neutral compound [{Li(thf)}3(µ3-Br)3(µ3-OSiMe3)Cd{C(SiMe3)3}](3), also with a cage structure, is obtained. Both (2) and (3) can be converted into CdBr{C(SiMe3)3}, and Cd(OH){C(SiMe3)3}. The chloride CdCl{C(SiMe3)3} is dimeric in the gas phase. The reaction between tris(dimethylphenylsilyl)methyl-lithium and cadmium(II) bromide yields the cadmate Li(thf)2CdBr2{C(SiMe2Ph)3} which can be converted into Cd(OH){C(SiMe2Ph)3}, CdBr{C(SiMe2Ph)3}, or Cd(OMe){C(SiMe2Ph)3}. The reaction between Li{C(SiMe3)3} and anhydrous manganese(II) chloride gives the trimanganate [Li(thf)4][{Mn[C(SiMe3)3]}3(µ-Cl)4(thf)], in which the anion has been shown by X-ray diffraction to have a cage structure related to that of the anion in (2). In each C(SiMe3)3 group the three SiMe3 fragments are twisted from fully staggered positions so the group as a whole is chiral. In some tris(trimethylsilyl)methylmetal compounds left- and right-handed C(SiMe3)3 groups alternate in the crystal lattice; in other chiralities are arranged randomly.

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