The molecular structure of bis(bis(trimethylsilyl)amido) magnesium, Mg{N(Si(CH 3) 3) 2} 2, as determined by gas-phase electron diffraction: a sterically hindered magnesium amide

Abstract

Gaseous bis(bis(trimethylsilyl)amido) magnesium, Mg{N(SiMe 3) 2} 2, has been studied by electron diffraction at a nozzle temperature of ca 400 K. The diffraction data are consistent with a model including only monomers. Important structural features of the equilibrium conformation of the monomer are the linear NMgN arrangement and the staggered Si 2NMgNSi 2 backbone. The ligands undergo large-amplitude vibration about the NMgN axis, and the barrier to internal rotation is 3(1) kcal mol −1. Principal bond lenghts ( r a) and valence angles are: MgN 1.91(3) Å, SiN 1.703(6) Å, SiC 1.886(5) Å; ∠SiNSi 132(2)°, ∠MgNSi 114.0(1.2)°, ∠NSiC 116.4(1.2)° and ∠SiCH 111.3(1.5)°. The SiMe, groups are twisted 14(4)° away from the reference position typified by one SiC bond of each such group eclipsing the adjacent MgN bond, while the methyl groups themselves are twisted 9(9)° away from their staggered reference positions. These torsional distortions lower the overall symmetry of the molecule from D 1d to S 4.