Synthesis and crystal structure of an assembly of three ortho‐carborane cages linked via para‐phenylene units: effect of aryl orientation on cage CC bond lengths in C‐aryl‐ortho‐carboranes

Abstract

The synthesis and crystal and molecular structure are described of (C 2 B 10 H 11 )C 6 H 4 (C 2 B 10 H 10 )C 6 H 4 (C 2 B 10 H 11 ) (4), an acyclic assembly of three ortho-carborane units connected through their carbon atoms by two para-phenylene units. For this compound, and published structures of other arylortho-carboranes, correlations are noted between the orientations of aryl substituents and cage carbon-carbon distances (C1-C2). Ab initio RHF/6-31G * and MP2/6-31G * studies on 1-phenylortho-carborane, PhC 2 B 10 H 11 , and other model systems have been used to explore the variations in their energies, C1-C2 bond lengths, and C2-C1-C aryl bond angles with the orientation of their aryl groups, variations believed to reflect weak interactions between the aryl substituents' π systems and the carborane cages. The synthesis of a pentafluorophenyl derivative of 4,

Studies on bis(1′-ortho-carboranyl)benzenes and bis(1′-ortho-carboranyl)biphenyls

“…A cage C-C bond length of around 1.64 Å is expected when the torsion angle θ is small. 15 In the reported crystal structures of 1, the cage C-C bonds are 1.640(5) and 1.649(2) Å with the torsion angles θ of 18.3º and 22.3º respectively. 24 In the crystal structure of 2 the C(4')-C(5') bonds of benzene rings of adjacent molecules are antiparallel with the shortest interatomic C…C(1-x,-y,1-z) distance of 3.40 Å, that probably indicates the presence of π…π interactions ( Figure 6).…”

“…or misfit procedure, 15,23 using the ofit command in XP within the SHELXTL package, 31 was applied between the experimentally determined molecule of 7 and the four MP2-optimised conformers a-d. The lower the misfit value (Å) is calculated, the better the fitting is.…”

Sulfur, tin and gold derivatives of 1-(2′-pyridyl)-ortho-carborane, 1-R-2-X-1,2-C2B10H10(R = 2′-pyridyl, X = SH, SnMe3or AuPPh3)

“…24,25 This was further explored by ab initio RHF/6-31G* and MP2/6-31G* calculational studies on 1-phenylortho-carborane and other aryl-carboranes in order to probe the orientational preferences of aryl groups attached to the carbon atoms of ortho-carborane. 26,27 These calculations have indicated that, although the overall energy of an aryl-carborane may vary only slightly with the aryl group orientation, the latter does have a perceptible influence on the C(1)-C(2) bond distance, which is greatest when the aryl group is aligned perpendicular to the aryl C-C(1)-C(2) plane. This is because this orientation optimises transfer of electronic charge from the filled π orbitals of the aryl group into a cage LUMO that is σ-antibonding with respect to the cage bond C(1)-C(2).…”

Exo-π-bonding to an ortho-carborane hypercarbon atom: systematic icosahedral cage distortions reflected in the structures of the fluoro-, hydroxy- and amino-carboranes, 1-X-2-Ph-1,2-C2B10H10 (X = F, OH or NH2) and related anions

“…In 2-phenyl-ortho-carborane itself, PhCb o H (Fig 1(a), R = Ph, X = H), the hypercoordinated carbon ('hypercarbon' 6 ) atom C1 forms a single bond to the exohydrogen atom and bonds of lower order to the five neighbouring cage atoms (one carbon, four borons). As the order of the exo-C-X bond increases from one to two, we 3 shall show how the bond to the neighbouring cage carbon atom is particularly affected, 4,8 When the aryl planes are roughly perpendicular to the ipsoC-C1-C2 plane (as preferred sterically in diaryl derivatives) the skeletal C1-C2 distance is longer than for other ring orientations. Involvement in exo C1-Cipso dative -bonding from the aryl -system reduces the capacity of the appropriate tangential p AO on C1 for C1-C2 skeletal -bonding ( Fig.…”