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

The synthesis and crystal and molecular structure are described Of (C2B10H11)C6H4(C2B10H10)C6H4 (C2B10H11) (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 aryl-ortho-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-phenyl-ortho-carborane, PhC2B10H11, 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' pi systems and the carborane cages. The synthesis of a pentafluorophenyl derivative of 4, (C2B10H11)C6H4(C2B10H10)C6H4(C2B10H10)C6F5, is also described

Big macrocyclic assemblies of carboranes (big MACs): synthesis and crystal structure of a macrocyclic assembly of four carboranes containing alternate ortho- and meta-carborane icosahedra linked by para-phenylene units.

The macrocyclic compound, [1,2-C2B10H10-1,4-C6H4-1,7-C2B10H10-1,4-C6H4](2) (5)-a novel cyclooctaphane, was prepared by condensation of the C,C'-dicopper(l) derivative of meta-carborane with 1,2-bis(4-iodophenyl)-ortho-carborane. The X-ray crystal structure of 5.C6H6-6C(6)H(12) was determined at 150 K, revealing an extremely loose packing mode. Molecule 5 has a crystallographic C-s and local C-2r symmetry; the macrocycle adopts a butterfly (dihedral angle 143degrees) conformation with the ortho-carborane units at the wingtips and the phenylene ring planes roughly perpendicular to the wing planes. Multinuclear NMR spectra suggest that molecule 5 in solution inverts rapidly via the planar D-2h geometry, which (from ab initio HF/6-31G* calculations) is only I kcal mol(-1) higher in energy than the C-2r. one. An attempt to prepare an even larger macrocycle, comprising three para-carborane and three ortho-carborane units linked by six para-phenylene units, was unsuccessful

New synthetic and structural studies on nitroso-ortho-carboranes RCB10H10CNO and bis(ortho-carboranyl)amines (RCB10H10C)(2)NH (R = Ph or Me)

Improved procedures are reported for the preparation of nitroso-carboranes RCb°NO (Cb° = 1,2-C2B10H10; R = Ph, Me at cage carbon C2) in 44–77% yield, and of dicarboranylamines (RCb°)2NH in 55–65% yield by reactions between the lithio-carboranes, RCb°Li and nitrosyl chloride, NOCl, in cold mixtures of diethyl ether and either pentane (for RCb°NO) or dimethoxyethane (for (RCb°)2NH). Deprotonation of the amines by KOtBu in toluene in the presence of 18-crown-6, (CH2CH2O)6, affords the salts [K(18-crown-6)]+[(RCb°)2N]−. X-ray crystal structures of PhCb°NO, (PhCb°)2NH, (MeCb°)2NH and [K(18-crown-6)]+[(PhCb°)2N]− are described, and the bonding implications of their cage C…C distances (1.68, 1.80, 1.75 and 1.99 Å, respectively) are discussed. These species provide further striking examples of the remarkable capacity of the ortho-carborane cage to act as a sensitive indicator of the π-donor characteristics of ligands attached to its cage carbon atoms

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

Reactions between the C,C’-dicopper(I) derivative of ortho-carborane and ortho-, meta- and para-diiodobenzene are reported. The reaction with 1,2-C6H4I2 unexpectedly afforded 2,2’-bis(1’-ortho-carboranyl)biphenyl, [HCB10H10CC6H4]22, whereas reactions with 1,3- or 1,4-C6H4I2 provided alternative routes to 1,3-bis(1’-ortho-carboranyl)benzene 3 and 1,4-bis(1’-ortho-carboranyl)benzene 4 respectively. The crystal structure of the biphenyl derivative 2 revealed significant distortions in the biphenylene framework attributable to the proximity of the two bulky carborane cages. UV absorption spectra and electrochemical data on 2 and 3 showed little electronic communication between the two carborane cages in either, and negligible pi-conjugation between the two ortho-phenylene rings in 2. However, substantial evidence was found of electronic communication between the carborane cages via the para-phenylene bridge in 4. B3LYP/6-31G* computations have been carried out on compounds 2 and 4, on 4,4’-bis(ortho-carboranyl)biphenyl 6 and on 1,2-bis(1’-ortho-carboranyl)benzene 7. Those on 2, 4 and 6 show the computed geometries to be in very good agreement with the experimental geometries: those on 7 allowed the reported molecular geometry of this compound to be revised and revealed a long cage C-C bond of 1.725(3)A

Intra- and inter-molecular carboranyl C-H center dot center dot center dot N hydrogen bonds in pyridyl-containing ortho-carboranes

Four C-substituted derivatives of ortho-carborane, 1-R-1,2-C2B10H11, where R = 2'-pyridyl (1), 2'-picolyl (2), 5'-bromo-2'-pyridyl (3) or 3'-pyridyl (4) have been prepared using adaptations of standard procedures, and structurally characterised by single crystal X-ray diffraction studies in an exploration of C-H...N hydrogen bonding effects involving their carborane CH units. Calculations at the MP2/6-31G* level of theory were used to assess the strength of the hydrogen bonding detected, and calculated NMR shifts at the GIAO-B3LYP/6-311G* level were compared with measured C-H shifts to show that intramolecular C-H...N hydrogen bonding persisted in solution in the case of compound 1. The value of IR C-H stretching frequencies for probing hydrogen bonding in these systems was also studied. An unsuccessful attempt to convert compound 3 into a macrocyclic species (C2B10H10C5H3N)(3) in which three ortho-carborane units are linked through 2,5-disubstituted pyridine rings is also described

Substituent Effects on the Fluorescence Properties of ortho-Carbor­anes: Unusual Emission Behaviour in C-(2′-Pyridyl)-ortho-carboranes

Seventeen compounds including the parent ortho-, meta- and para-carboranes and derivatives of ortho-carborane were investigated for luminescence in cyclohexane and dichloromethane solutions. Fifteen of these carboranes revealed very weak emissions in the 285–493 nm range. These carboranes may arguably be viewed as non-emissive in solutions at room temperatures. No emissions could be observed for 1,2-dimethyl-ortho-carborane and 2-methyl-1-phenyl-ortho-carborane. The carboranes with a 2′-pyridyl substituent at the cluster carbon atom gave unusual local and charge-transfer emissions indicating that different excited states are generated on photoexcitation. Of all the carboranes investigated, only 2-(diphenylphosphino)-1-phenyl-ortho-carborane, 1,2-diphenyl-ortho-carborane and 1-phenyl-2-(2′-pyridyl)-ortho-carborane are luminescent in the solid state with emissions at 476–612 nm and large Stokes shifts of 12000–13600 cm–1. The solid-state structures of 1,2-bis(2′-pyridyl)- and 1-phenyl-2-(2′-pyridyl)-ortho-carborane were determined by X-ray crystallography

Preparative and structural studies on sulfur-linked carborane icosahedra: 2-phenyl-ortho-carboranyl-sulfur systems (2-Ph-1,2-C2B10H10)(2)X (X = S, S-2 or SO), and ortho-carboran-di-yl systems (1,2-C2B10H10Y)(2) (Y = S or SO)

Details are reported of the preparation and X-ray structural characterisation of the new compounds (PhCbo)2X, where PhCbo = 2-Ph-1,2-C2B10H10 and X = S (1) or SO (3), prepared from PhCboLi and SCl2 or SOCl2 respectively, as well as the known compound with X = S2 (2). Hydrogen in the presence of palladium/carbon reduced (3) to (1). Features of their structures (exo C–S and cage C–C distances and substituent orientations) are consistent with significant exo Sdouble bond; length as m-dashC dative π-bonding from their sulfur atoms to the cage hypercarbon atoms and weak exo π-bonding from the phenyl groups. Attempts to prepare systems (CboY)2, in which two ortho-carboran-di-yl residues Cbo are linked through two bridging units Y (S, SO) are also reported, as are their calculated structures