Trishomoaromatic Dianions of 1,3,5-Triboracyclohexanes

Abstract

A new trishomoarene is obtained by reduction of hexamethyl‐1,3,5‐triboracyclohexane with lithium in donor solvents. Addition of tetrahydropyran (THP) and [12]crown‐4 yields crystalline tetramers (the structure of the tetrameric anion obtained with [12]crown‐4 is shown). The B3 rings are aromatic.

Reductions of 1,3,5-Triboracyclohexanes and Related 1,3,5-Triboraalkanes with Alkali Metals to Trishomoaromatic Aggregates — Tetrameric Lithium and Sodium, and Polymeric Sodium and Potassium Trishomoaromatic Cyclotriborate Compounds

“…[1] Remarkable results such as the synthesis of the doubly-aromatic anion 1 with σ and π 3c,2e bonding have been reported by Berndt et al [2,3] Recently we obtained the new, trishomoaromatic system 3 by reducing 1,3,5-triboracyclohexanes 2 with lithium. [4,5] The empty p-orbitals of 2 are able to accept two electrons to form the dianion 3, which is isoelectronic with the trishomocyclopropenylium cation 6. [6] We now describe the reactions of the hexamethyl derivative 2 with various alkali metals and the influence of these metals on the structures and on the NMR chemical shifts of the trishomoaromatic dianions 3.…”

“…Stabilization energies (kcalmol Ϫ1 at //B3LYP/6Ϫ311ϩG**) and NICS values (at PW91/IGLO III) [4] for the trishomoaromatic systems 3Ϫ6 RЈ ϭ H), which is larger than all three of the isoelectronic counterparts 4Ϫ6 (Table 2), even when evaluated by two different methods. [12] These stabilization energies are based on the isodesmic reactions in Scheme 5 and the chair (delocalized)Ϫboat (localized) energy differences.…”

Elektronen‐defizitäre Triboran‐ und Tetraboran‐Ringverbindungen: Synthese, Struktur und Bindung

“…Diese Verbindungen sind ebenfalls isoelektronisch zum Trishomocyclopropenylium‐Kation . Schema a zeigt als Beispiel die Synthese von [B 3 Me 3 (C(H)Me) 3 ] 2− , das einen tetrameren Ring bildet, bei dem die [B 3 Me 3 (C(H)Me) 3 ] 2− ‐Einheiten über Li + ‐Ionen miteinander verknüpft sind . Schema b zeigt ein Beispiel mit zwei “nicht‐klassischen” (3c,2e)‐B‐H‐B‐Homobrücken von Paetzold et al …”

“…Eine eingehende theoretische Analyse wies auf fast gleich große σ‐ und π‐Beiträge zur Bindung zwischen den drei Boratomen hin; also liegt die Verbindung zwischen einem σ‐ und einem π‐Homoaren (σ/π‐gemischtes Homoaren) . Mehrere strukturell und elektronisch zu (B 3 H 6 ) + verwandte Verbindungen wurden synthetisiert, insbesondere solche, bei denen die “nichtklassischen” (3c,2e)‐B‐H‐B‐Homobrücken teilweise oder vollständig durch klassische Brücken (zwei (2c,2e)‐Bindungen unter Einbeziehung von zwei Boratomen des B 3 ‐Rings) ersetzt sind …”

Adventures in Tin(II) phosphinidene chemistry; insights into the mechanism of P–P and Sn–Sn bond formation

“…6). The electronic structure of this species, which can be regarded as part way between the electron precise arrangements of Sn(II) phosphinidene cages and the delocalised electron structure of a metal, is related to that of the cycloproponium cation and trishomoaromatics of boron reported by Siebert and von Schleyer [14]. Irrespective of the stoichiometry, the analogous reaction of Sn(NMe 2 ) 2 with CyPHK gives [Sn 2 (l-PCy)(l-CyPPCy) 2 ](K AE 2thf) 2 (10) (Fig.…”