Benzocarborane

Synthesis, Structure, and Reactivity of 1,2-(1‘,1‘,2‘,2‘-Tetramethyldisilane-1‘,2‘)carborane

“…o -Carborane has been described as “superaromatic” due to the delocalized nature of the bonding in the framework. ,, In the case of thermal stability and electrophilic substitution reactions, o -carborane acts similarly to arenes. There are also examples of fused aryl- o -carborane compounds where there is evidence that the electrons are delocalized throughout the structure . However, the poor overlap between the delocalized MO of the carborane framework and the “p-like” orbitals needed from the sp 2 silicon must inhibit any significant resonance contribution of an o -quinonedisilane-type for 1 .…”

The enhanced structural carborane effect

“…1) and first prepared by Matteson [9] and studied crystallographically by Wade et al [10] A fundamental question concerning I is the degree of aromatic character associated with the exopolyhedral C 6 ring. Based primarily on 1 H NMR spectroscopy Matteson concluded that the ring has little aromatic character, a view echoed by Wade et al from their analysis of CeC distances and calculated p-bond orders.…”

“…Such a compound would be H2-II, the dihydro analogue. This is a derivative of 1,2-m-(C 4 H 6 )-1,2-closo-C 2 B 10 H 10 , "dihydrobenzocarborane" (H2-I), also prepared by Matteson [9] and studied structurally by Wade [10]. But in comparing II and H2-II the C cage eB distances as well as the C cage eM3 distances should be susceptible to any enhanced structural carborane effect.…”

Reactions of 1,2-Dehydro-o-carborane with Thiophenes. Cycloadditions and an Easy Synthesis of “Benzo-o-carboranes”1

“…Removal of the solvent at the rotary evaporator gave a yellow semisolid, which was then chromatographed (SiO 2 /hexanes) to yield a white solid. After recrystallization from aqueous ethanol, colorless needles of benzo- o -carborane ( 2 ) were obtained (0.51 g, 19%): mp 111−112 °C (lit . 110 °C); 1 H NMR (CDCl 3 , 300 MHz) δ 1.10−3.40 (br m, 10 H, BH), 6.27 (m, 2 H), 6.48 (m, 2 H).…”

“…This exquisite compound was first made in 1968 by Matteson and his collaborators by a double displacement of 1,2-dilithio-ocarborane on 1,4-dibromobut-2-ene, followed by an oxidation procedure. 14 Our reaction constitutes an extremely simple route to these compounds in which a 1,3-diene is appended to the icosahedron in a union that might well be regarded as miscegenetic. We assumed that an intermediate of structure 3 was first formed but were unable to isolate it.…”