Two-electron aromatics containing three and four adjacent boron atoms

Abstract

A two-electron aromatic bis(tris-trimethylsilylmethylene)-substituted tetraborane(4) was found to be a useful precursor for the synthesis of two-electron aromatic tetraboranes(6), triboracyclopropanates, as well as tetraboranes(6) distorted toward triboracyclopropanates with boryl bridges. Bishomo two-electron aromatics with a borata bridge and a protonated borata bridge, respectively, are also presented.

A Radical Tricationic Rhomboid Tetraborane(4) with Four‐Center, Five‐Electron Bonding

“…The derivative bicyclotetraborane(4) [B(NMe 2 )] 2 [B{B(NMe 2 ) 2 } 2 ] ( 4 ; see Scheme ) with a transannular B−B bond distance of 1.633(1) Å was synthesized and structurally characterized. While dicationic tetraborane(4) [B 4 H 4 ] 2+ (SE=6) or derivatives are unknown, the tetraborane(6) 5 (also with SE=6, see Scheme ) was synthesized and is the rhomboid tetraborane with the shortest experimentally verified transannular B−B bond (1.511(3) Å) . Quantum‐chemical calculations predict a decrease of the transannular B−B distance with decreasing SE (SE≥6).…”

Electron‐Deficient Triborane and Tetraborane Ring Compounds: Synthesis, Structure, and Bonding

“…Consequently,t hese compounds are both sand p-homoaromatic compounds [(p + s)-double aromatic]. [5,28] These compounds are related to an isomer (also C 2v -symmetric) of (B 3 H 4 ) À that is slightly higher in energy than the global energy minimum structure.T hey exhibit both s-a nd p-delocalized electron systems,and can thus be classified as (p + s)-double aromatic compounds. [26] Formal monoprotonation of (B 3 H 3 ) 2À leads to (B 3 H 4 ) À (Scheme 4).…”

Ein radikaltrikationisches Tetraboran(4) mit rhombischer Struktur und Vier‐Zentren‐fünf‐Elektronen‐Bindung

“…Das entsprechende Bicyclotetraboran(4) [B(NMe 2 )] 2 [B{B(NMe 2 ) 2 }] 2 ( 4 ; Schema ), mit einer transannularen B‐B‐Bindungslänge von 1.633(1) Å, konnte hergestellt und strukturell charakterisiert werden. Während das dikationische Tetraboran(4) [B 4 H 4 ] 2+ (GEZ=6) oder entsprechende Derivate nicht bekannt sind, konnte das Tetraboran(6) 5 (ebenfalls mit GEZ=6, Schema ) mit der bislang kürzesten experimentell gefundenen transannularen B‐B‐Bindung (1.511(3) Å) synthetisiert werden . Quantenchemische Rechnungen sagen eine Abnahme des transannularen B‐B‐Abstands mit kleiner werdender GEZ voraus (GEZ≥6).…”