Reaktionen der Azadiboriridine: Clusterbildung und Ringerweiterung

Reactions of the Azadiboriridines: Formation of Clusters and Ring Expansions* Nine bis(haloboryl)amines 1 were synthesized by haloboration of iminoboranes RB = NR” with dihaloboranes R'BHal2 [R/R'/R” = Et/iPr/tBu (1b), Et/sBu/tBu (c), iPr/iPr/iPr (d), iPr/tBu/iPr (e), tBu/Me/tBu (g), tBu/Et/tBu (h), tBu/Et/SiMe3 (k), tBu/tBu/SiMe3 (1), tBu/Cl/tBu n)]. The borane 1n can be transformed into 1o (R' = NMe2) by the reaction with Me3SiNMe2; an equilibrium between 1o and the four‐membered ring 1o' is observed, 1o' being formed from 1o by intramolecular B – N coordination. On reduction with lithium, the nido‐diazahexaboranes 3b–e, g, h are formed from the corresponding bis‐(haloboryl)amines 1. In the case of 3e, g, h, the ligands R and R' are unsymmetrically distributed to axial and equatorial positions of the fragment structure derived from the pentagonal bipyramid. In particular cases, azadiboriridines of type 2 are either isolated or proven as intermediates on the way from 1 to 3. The three‐membered ring of the known azadiboriridines 2i, m (R/R'/R” = tBu/iPr/tBu, tBu/tBu/tBu) is expanded to the five‐membered ring of the corresponding azadiborolines 4i, m by the reaction with 3‐hexyne. The products 4i, m are reduced to the dilithium azadiborolinates 5i, m by the action of lithium; the molecular structure of a closo‐azadicarbadili‐thiaheptaborane is recognized in crystals of 5i. The threemembered ring of 2m is also expanded by the reaction with the iminoborane EtB ≡ NtBu giving the diazatriborolidin 6m, which crystallizes in the space group Pca21