Two representatives of the three membered B2N-ring system have been obtained by dehalogenation of diborylamines Me3CN[BHalNR2]2. In solution there is no restricted rotation at the exocyclic BN bond, even at low temperature. In contrast, the X-ray structure analysis of the bis-tetramethylpiperidino derivative 10a reveals alternation of short and long BN bonds; one of the tetramethylpiperidino groups stands nearly coplanar with the B2N-ring system, the other, however, is almost perpendicular to the ring plane. The ring contains a short BB bond (1.612 Å).
The crystal and molecular structures of two trans-1,2,4,5-tetraza-diphospha-3,6-cyclohexane- 3,6-disulfides, 2 and 3, have been determined by X-ray diffraction methods. The 3,6-diphenyl- 1,2,4,5-tetramethyl-derivative 2 crystallizes in the monoclinic system, space group C He. Its P2N 4 heterocycle adopts a twist conformation. In contrast, the hexamethyl derivative 3 is triclinic, space group P1̅, and its ring shows chair conformation. Torsion angles in these two compounds and similar ones reveal less interaction between lone pairs of electrons on adjacent N-atoms in the chair conformation but stronger interaction of those bound to phosphorus. It is suggested that the latter interaction is responsible for the larger N -P -N bond angle (107°) as compared to the smaller one (101°) in the P2N4 rings present in twist conformation.
Die Titelverbindungen (IV) werden durch Enthalogenierung der Haloborierungsprodukte (III) von Aminoiminoboran (I) und den Aminobordihalogeniden (II) mittels einer Na/K‐Legierung synthetisiert.
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