Five- and Six-Coordinate Nitrogen in Azaborane Clusters

Abstract

In the majority of known azaboranes NaBbHc and their derivatives, the coordination number of the nitrogen atoms within the cluster does not exceed the classical values of 3 or 4. In the azaboranes closo‐NB9H10, nido‐NB10H13, and closo‐NB11H12 and in their derivatives, however, the nitrogen atoms are 5‐ or 6‐coordinate and thus represent a novel bonding situation. The synthesis, structure, and reactivity of these azaboranes are reviewed in this article.

Four Decades of Organic Chemistry of closo-Boranes: A Synthetic Toolbox for Constructing Liquid Crystal Materials. A Review

“…C-Amino substituted monocarbaboranes 20 and 21 have been obtained in good yields via borane insertion to The newest addition to the pool of closo-heteraboranes are the azaboranes 69 . Unlike the synthesis of 9 (ref.…”

“…70 ), the preparation of the parent [NB 11 H 12 ] (3) is rather inefficient and involves the dangerous hydrazoic acid 71 . N-Substituted derivatives are easily prepared using the corresponding amines and [B 9 H 13 (SMe 2 )] via the nido derivative 22 (Scheme 1) 69 . Subsequent thermal dehydrogenation of 22 yields ten-vertex derivatives 9R (ref.…”

“…The chemistry of azaboranes will be omitted in the following discussion. Although azaboranes 3 and 9 can be N-alkylated 80 and B-halogenated 81 they exhibit rather significant sensitivity to solvents and nucleophiles 69 and their usefulness for materials purposes is questionable 74 .…”

Aza-nido-dodecaboranes and -borates from Aza-closo-dodecaboranes by the Addition of Neutral or Anionic Bases: Mechanism

“…Neutral bases L or anionic bases X Ϫ can add their lone pair to one of the ortho-BH vertices under opening of two neighbouring BϪN bonds, accompanied by the migration of the corresponding exo-H atom into a bridging position. The resul- A mechanism for the reaction of closo-RNB 11 H 11 with bases had been proposed [2], which leaves the base in a fixed position at the primarily attacked vertex, whereas the extra-proton jumps from endo into bridging positions and vice versa, and the RN apex builds and breaks BϪN bonds around the pentagon B2ϪB5ϪB8ϪB9ϪB4 (i.e. the orthobelt B2ϪB3ϪB4ϪB5ϪB6 in the former closo-structure), until the final isomer 7 is formed via the endo-H containing isomers 2, 4, 6 and the bridge-H containing isomers 3 and 5 (Fig.…”

“…We used external standards for 11 B (BF 3 (OEt 2 )) and 19 F (CFCl 3 ); residual protons and 13 C atoms of the deuterated solvents acted as standards for 1 H and 13 C, respectively, converted finally into the common tms standard. CD 2 Cl 2 was the solvent, but [D 8 ]thf was used for 1a, 1a·py, 1a·NH2 tBu, Li[1dMe], and Na{1a [FeCp(CO) 2 ]} and a diluted solution of H 2 O in MeOD for H[1f(OH)]. COSY 45 was applied for pulse recurrence in 2D-11 B/ 11 B NMR spectra; cluster-exo-H atoms were assigned with the aid of 2D-1 H/ 11 B HMQC.…”