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 [Li(TMEDA) {C(SiMe3)(2)SiMe(2)NMe2}] (1) (TMEDA = N,N,N',N'-tet ramethylethane-1,2,-diamine) was found to crystallise with an internally co ordinated structure like that of [Li(THF)(2){C(SiMe3)(2)SiMe2Me2}] (THF = t etrahydrfuran). In contrast, the compound with Ph in place of NMe2 crystall ised as a dialkyllithate [Li(TMEDA)(2)][Li{C(SiME3)(2)(SiMe2Ph)}(2)] (4). T he reaction of 4 with MgBr2 gave the doubly bromide-bridged lithium-magnesi um complex [Li(TMEDA)(mu -Br)(2)Mg{C(SiMe3)(2)(SiMe2Ph)} (THF)] (6), and th at of [Li(THF){C(SiMe3)(2)(SiMe2C5H4N-2)}] gave the singly bridged compound [Li(THF)(3)(mu -Br)MgBr{C(SiMe3)(2)(SiMe2C5H4N-2)] (8). The Grignard reage nts [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)(3)CI and (Me2Ph) (Me3Si)CI, respectively, with magnesium metal and shown to have halide-brid ged structures. The unsymmetrical dialkylmagnesium [MgBu{C(SiMe3)(2)(SiMe2N Me2)}(THF)] (13), was prepared from a mixture of LiBu, 1 and [MgBr2(OEt2)(2 )]. (C) 2001 Elsevier Science B.V. All rights reserved.