Highly Hindered Amido-Lithium and Amido-Magnesium Complexes. Crystal-Structures of [Li(Mu-N(SiMe3)2)(Tetrahydrofuran)]2 and [MgBu^s(Mu-N(SiMe₃)₂)]2

Abstract

Treatment of hexamethyldisilazane in thf (tetrahydrofuran) with LiBu in hexane yields [Li{μ-N(SiMe₃)₂}(thf)]₂, (1). MgBu⁸Bu in heptane with hexamethyldisilazane results in initially formation of [MgBu^s(μ- N(SiMe₃)₂}]₂, (2), then ?Mg{N(SiMe₃)₂}₂,(3). The structures of (1) and (2) have been determined by X-ray diffraction. Remarkably, they are isomorphous: crystals are tetragonal, space group P4n2 with a 9.970(7), c 16.753(9) Ǻ for (1), and a 9.524(6), c 17.385(9) Ǻ for (2), with Z = 2. The lattices are comprised of discrete molecules with symmetry 222, and thus Bu^s disorder in (2), yith the amido ligands bridging three- coordinate metal centres [Li-N 2.025(9), Li-O 1.882(14) Ǻ, Li-N-Li 73.7(5)°, N-Li-N 106.3(6)°, O-Li-N 126.8(3)° (1); Mg-N 2.118(4), Mg-C 2.08(1) Ǻ, Mg-N-Mg 87.1(2)°, N-Mg-N 92.9(2)°; C-Mg-N 133.6(1)°(2)].