N,N-dimethyl(trimethylsilyl)amine: crystal and molecular structure at 116 K and gas phase structure by electron diffraction

Abstract

The structure of NMe₂(SiMe₃) has been studied in the crystalline phase at 116 K by X-ray crystallography and in the gas phase at 295 K by electron diffraction. The solid phase structure consists of essentially isolated molecules with a Si–N bond length of 1.719 4(12)Å. The geometry at silicon is nearly tetrahedral and that at nitrogen is slightly non-planar, with angles CNC 111.95(12), SiNC 122.92(10) and 122.91(10)°. The molecule possesses non-crystallographic C_s symmetry and the N-bonded methyl groups are distorted from planarity towards the unique Si-bonded methyl group, which is bent back to give an NSiC angle of 113.93(6)°. The conformation of the Si-methyl groups is such that one CH vector of each is approximately parallel to the NSi direction; for those bonded to nitrogen, one CH bond of each lies close to the CSiN plane. In the vapour the SiNC₂ skeleton was found to be planar. Principal parameters (r_a) are: r(Si–N) 1.710(5), r(Si–C) 1.868(4), r(C–N) 1.462(4)Å; angles SiNC 121.4(5), NSiC 110.3(7), CNC 117.1(10)°. The molecule is distorted from C_s symmetry by a 9.6(20)° twist of the SiMe₃ group and by twists of –12.1(45)° for each of the methyl groups on silicon.