Crystal structures of organometallic compounds of lithium and magnesium containing the bulky ligands C(SiMe3)2(SiMe2X) X=Me, Ph, NMe2, or C5H4N-2

The complex [Me2}] (1) (TMEDA=N,N,N′,N′-tetramethylethane-1,2,-diamine) was found to crystallise with an internally coordinated structure like that of [Me2}] (THF=tetrahydrfuran). In contrast, the compound with Ph in place of NMe2 crystallised as a dialkyllithate [Li(TMEDA)2][Li{C(SiMe3)2(SiMe2Ph)}2] (4). The reaction of 4 with MgBr2 gave the doubly bromide-bridged lithium–magnesium complex [Li(TMEDA)(μ-Br)2Mg{C(SiMe3)2(SiMe2Ph)}(THF)] (6), and that of [-2)}] gave the singly bridged compound [Li(THF)3(μ-Br)-2)] (8). The Grignard reagents [Mg{C(SiMe3)3}I(OEt2)]2 (10) and [Mg{C(SiMe3)2 (SiMe2Ph)}I(OEt2)]2 (11) were obtained from the reactions between (Me3Si)3CI and (Me2Ph)(Me3Si)CI, respectively, with magnesium metal and shown to have halide-bridged structures. The unsymmetrical dialkylmagnesium [Me2)}(THF)] (13), was prepared from a mixture of LiBu, 1 and [MgBr2 (OEt2)2].