The Pyramidal Si₂N−O Skeleton of <i>O</i>-Methyl-<i>N</i>,<i>N</i>-disilylhydroxylamine:  An Inherent Phenomenon As Confirmed by Structural Studies in Different Phases

Abstract

O -Methyl- N, N -disilylhydroxylamine, (H 3 Si) 2 NOCH 3 ( 1 ), has been prepared by the reaction of bromosilane with O-methylhydroxylamine in the presence of 2,6-lutidine. The compound has been found to be reasonably stable at ambient temperature, but explodes if heated to 200 °C. 1 has been completely characterized by MS, HRMS, IR in the solid state and gas phase, and NMR spectra of the nuclei 1 H, 13 C, 14/15 N, 17 O, and 29 Si. The NMR chemical shifts are compared with those of Si-methylated derivatives and with values obtained in high-level ab initio calculations. It has been concluded that there is close similarity between the structure in solution and the calculated one. A single crystal of 1 grown in situ and studied by X-ray diffraction is orthorhombic, space group P 2 1 2 1 2 1, a = 6.3664(11) Å, b = 8.488(2) Å, c = 11.783(4) Å, ρ calc = 1.119 g cm - 1, Z = 4. Intermolecular Si···O interactions (2.92 Å) are found in the solid state structure leading to a zigzag type aggregation of the molecules. The gas phase structure of 1 has been determined by electron diffraction showing the molecule to have C s symmetry. In both phases, the crystalline and the gas phase, the nitrogen atom configuration of 1 is pyramidal [∑<(N) GED 351.8(12)°, XRD 352.8(3)°], showing this to be an inherent feature of N -silylated hydroxylamines and not caused by packing forces. Most of the geometrical parameters are consistent for both phases showing that the intermolecular Si···O interactions cause only minor structure distortions. The structural results are discussed in comparison with ab initio calculated geometries, and it is concluded that the exceptional nitrogen configuration is caused by repulsion between the nitrogen and oxygen lone pairs of electrons.