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

Abstract

O-Methyl-N,N-disilylhydroxylamine, (H3Si)2NOCH3 (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 1H, 13C, 14/15N, 17O, and 29Si. 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 P212121, a = 6.3664(11) Å, b = 8.488(2) Å, c = 11.783(4) Å, ρcalc = 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.

A Steeply Pyramidal Silylamine: N,O-Dimethyl-N-silylhydroxylamine

“…The fact that this chemical shift is not between the resonances of (H 3 Si) 2 NOMe and MeNOH (−267.6 ppm; a chemical shift for Me 2 NOMe, which should be preferred for comparison, is not available) could be an indication for an unusual Si−N bonding situation, which would occur if the nitrogen atom is markedly pyramidal and thus hybridized differently than in most silylamines, including the only slightly pyramidal (H 3 Si) 2 NOMe. The proton-decoupled signal has a line width smaller than 1 Hz, which does not reflect the behavior of the signals caused by the silicon nuclei and silyl protons, and thus a Si···O interaction in solution should be favored, as is paralleled by the Si···O contacts found in the crystal structure of (H 3 Si) 2 NOMe …”

“…The nitrogen−oxygen bond vector encloses an angle of 57.2(13)° with the N3/Si4/C5 plane, corresponding to a deviation of the nitrogen atom of 0.476 Å from the O2/Si4/C5 plane. The coordination in H 3 SiMeNOMe is thus markedly more pyramidal than that in (H 3 Si) 2 NOMe, with the nitrogen−oxygen bond vector enclosing an angle of 33.2(25)° relative to the NSi 2 plane and the sum of angles at the nitrogen atom being 351.8(12)° 4 Molecular structure of H 3 SiMeNOMe as determined by gas-phase electron diffraction. …”

“…Moreover, the nitrogen coordination can be forced to be pyramidal by incorporation into a small ring cycle such as aziridine as a result of ring strain . For acyclic strain-free systems, it was only recently established that the pyramidal nitrogen coordination is an inherent phenomenon in the chemistry of silylhydroxylamine derivatives. , (H 3 Si) 2 NOMe, the simplest compound of this class prepared so far, has been studied in both the gas phase and the solid state to prove this . However, the examples studied so far were always doubly silylated at nitrogen and showed only slight deviations from planarity: the sum of angles at the nitrogen atoms never fell below 350°, and the corresponding declination of the N−O vector from the NSi 2 plane never exceeded ca.…”

Synthesis, Properties, and Structure of Poly(silyl)pyridines. The Phantom of Intramolecular Si−N Bonding

“…There are many very pronounced differences in the chemistry of carbon and silicon compounds, and these differences are perhaps best reflected in a comparison of simple methyl and silyl analogues with the C/Si atoms solely substituted by hydrogen (CH 3 /SiH 3 ). Classical examples are dimethyl ether versus methoxysilane and disiloxane, 1,2 trimethyl-versus dimethyl(silyl)-3 and trisilylamine, 4 methyl-versus silylhydrazines 5,6 and -hydroxylamines, 7,8 neopentane versus tetrasilylmethane, 9 methylated versus silylated ylides, 10 dimethylversus disilylnaphthalines, 11 or finally hexamethylversus hexasilylbenzene. 12 The reactivity pattern of the compounds not only is determined by the consequences of an umpolung of the E-H bond but also shows ready access to transition Organometallics 1998, 17, 4444-4453 S0276-7333(98) states with larger coordination numbers at silicon in nucleophilic substitution reactions or even to regular pentacoordinate silicon compounds as ground-state species.…”

O-Halogensilyl-N,N-bis(trimethylsilyl)hydroxylamine - Synthese, Kristallstruktur und Reaktionen

“…Sowohl ab initio Berechnungen der Geometrie [19,20] als auch Ro È ntgenstrukturanalysen [20,21] von N,N-Bis(silyl)-O-methylhydroxylaminen zeigen eine pyramidale Koordination am Stickstoffatom. Als Erkla È rung fu È r diese Befunde werden theoretische Studien [22] und die effektive Kernladung Z eff herangezogen [23].…”