Strukturbestimmungen an Bor–Stickstoff-Verbindungen. IV. Die Kristall- und Molekularstruktur von Hexakis(trimethylsilyl)-2,4-diamino-1,3,2,4-diazadiboretidin

Abstract

The title compound, a four-membered boron-nitrogen ring system, was investigated by X-ray methods.The crystals are monoclinic, space group P21/a with a=22.11, b= 14.96, c= 10.93/~, ~= 108"6 °, and four molecules in the unit cell. The structure determination is based on 3449 reflexion values, which were mainly obtained with the aid of an automatic diffractometer. Three-dimensional Patterson and Fourier syntheses were used for the structure determination. The structure was refined by least squares. The proposed structure could be confirmed. The four-membered.ring is planar, within the limits of accuracy of the determination, and the substituents on the N atoms are also arranged in a plane. The Si atoms attached to the exocyclic N atoms lie, however, not in the plane of the four-membered ring, but almost perpendicular to it. This can be attributed to steric factors. The following average bond lengths were found: B-N 1.45, N-Si 1.75, Si-C 1.87/~. The shortness of the exocyclic B-N bond is surprising since the substituent on the B and N atoms are arranged nearly perpendicularly to one another, not allowing the formation of a classical n-bond.

Synthesis of Complex Boron–Nitrogen Heterocycles Comprising Borylated Triazenes and Tetrazenes Under Mild Conditions

“…As our proposed quantum-chemically derived mechanism suggests, the reactivity we observed is consistent with the formation of transient novel boryl-substituted iminoboranes (Schemes and ). This is further supported by the observation of MesB­(X)-diazadiboretidine 7 , ,,,,− which is the dimer of the putative iminoborane 8_3 , by X-ray crystallography. Most iminoboranes are unstable with respect to dimerization, and diazadiboretidines are therefore typical byproducts of their formation.…”

Reactivity of Terminal Iron Borylenes and Bis(borylenes) with Carbodiimides: Cycloaddition, Metathesis, Insertion and C−H Activation Pathways

“…Recrystallization from hexane at À 30 °C yielded colorless crystals of all three dimers suitable for X-ray diffraction analysis (the structure of 11 SiMe3 is literature-known). [25] None of the products could be isolated in sufficient purity for further analyses. 11…”

“…In a similar way to the reaction with I, the addition of bis (trimethylsilyl)carbodiimide to the bis(borylene) complex II led directly to the formation of all three possible iminoborane dimers, the symmetrical 1,3,2,4-diazadiboretidines (Me 3 SiNBR) 2 (R=Dur 3 SiMe3 , N(SiMe 3 ) 2 11 SiMe3 ) and the unsymmetrical compound 13 SiMe3 resulting from the cycloaddition of [Me 3 SiN�BN-( SiMe 3 ) 2 ] and [Me 3 SiN�BDur]. These were identified by both their 11 B NMR shifts at 46.5, 27.0 and 38.0 ppm, respectively, as well as single-crystal X-ray crystallographic analyses of literature-known 11 SiMe3 , [25] and 13 SiMe3 (see Figure S52 in the Supporting Information).…”

Die 2,6‐Diisopropyl‐phenylgruppe als sperriger Substituent in Bor‐Stickstoff‐Verbindungen. II [1]

“…Die B-N-und Si-N-Bindungsabstande liegen mit 144,5 bzw. 174,4 pm in der gleichen GroDenordnung wie sie fur ein N-silyliertes Diazadiboretidin gefunden wurde [7].…”