Strukturchemie ungesättigter Siliciumverbindungen: Kristall- und Molekülstrukturen des stabilen Silanimins ′Bu2Si=N—Si′Bu3 und von Silanimin-Donoraddukten (Donor = Tetrahydrofuran, Benzophenon) / Structural Chemistry of Unsaturated Silicon Compounds: Crystal and Molecular Structures of the Stable Silaneimine ′Bu2Si=N—Si′Bu3 and of Silaneimine Donor Adducts (Donor = Tetrahydrofuran, Benzophenone)

Abstract

The structure of the first stable silaneimine ′Bu2Si=N—Si′Bu3 (1) (i.e. a compound containing a silicon nitrogen double bond) has been determined by X-ray crystallography (monoclinic, space group P21/n, a = 8.962(1), b = 18.361(1), c = 14.658(1) Å, β = 90.98(1)°, V = 2411.6 Å3.Z = 4, wR = 0.043, w = 1/σ2(Fo) for 208 refined parameters and 2610 observed structure factors. It is monomeric in the solid state and has a nearly linear Si=N—Si skeleton (Si—N—Si 177.8(2)°) with drastically different Si=N and Si—N bond lengths (1.568(3) and 1.695(3) A, respectively). The benzophenone adduct of ′Bu2Si=N—Si′Bu3 and the tetrahydrofuran (THF) adduct of the closely related silaneimine Me2Si=N—Si′Bu3 contain the donor molecules being coordinated exclusively to the unsaturated silicon atoms, which adopt a distorted tetrahedral coordination geometry upon coordination with characteristically elongated Si=N double bonds. The solid state structure of the benzophenone adduct strongly suggests that [2+2] cycloadditions of Si=N double bonds with aldehydes or ketones proceed in a non-concerted manner via prior formation of donor-Si bonds. ((THF) • Me2Si=N—Si′Bu3 (2): P21/n, a = 18.480(4), b = 14.209(2), c = 18.683(5) Å, β = 115.11(2)°, V = 4442.2 Å3, Z = 8, wR = 0.094 for 397 parameters and 3432 observables; (Ph2C=O) · ′Bu2Si=N—Si′Bu3 (3): P21,/n, a = 13.247(2), b = 15.689(2), c = 17.073(2) Å. β = 110.53(1)°, V = 3323.0 Å3, Z = 4, wR = 0.039 for 379 refined parameters and 3789 observables.)