Conformational control of benzyl-o-carboranylbenzene derivatives and molecular encapsulation of acetone in the dynamically formed space of 1,3,5-tris(2-benzyl-o-carboran-1-yl)benzene

A 1,3,5-substituted benzene platform has been widely used in the fields of supramolecular chemistry and molecular recognition. Here, we show that 1,3,5-tris(2-benzyl-o-carboran-1-yl)benzene 6 exhibits solvent-dependent conformation in the crystalline state. Recrystallization from dichloromethane-n-pentane gave the anti conformation 6-anti, while recrystallization from methanol-acetone gave the syn conformation 6-syn, in which the three benzyl-o-carboranyl moieties are located to one side of the central benzene ring. Interestingly, one acetone molecule is captured in the π-rich space of 6-syn and two complexes facing each other encapsulate two acetone molecules in a π-rich container formed by the eight benzene rings. The inclusion involves several weak interactions, that is, T-shaped C-H···π interactions, and C-H···O and C-H···π interactions. Two C-H···O interactions involving benzylic C-H hydrogens activated by the electron-withdrawing character of the o-carborane cage and the oxygen atom of the acetone seem to be the most important. DFT calculations indicate that the binding energy for entrapment of acetone is 6.6 kcal/mol. Inclusion of acetone is achieved through not only multiple C-H···O interactions but also a number of C-H···π interactions. The third benzyl-o-carborane moiety is fixed in the syn conformation by intramolecular and intermolecular C-H···π interactions.     

Distorted benzene bearing two bulky substituents on adjacent positions: structure of 1,2-bis(1,2-dicarba-closo-dodecaboran-1-yl)benzene

Synthesis and structural analysis of 1,2-bis(o-carboranyl)benzene were performed to examine the steric effects of the two extremely bulky o-carborane cages at adjacent positions on the planarity of the benzene ring. X-ray crystallographic analysis supported by DFT calculations revealed that the benzene ring is significantly deformed by the bulky o-carboranyl groups.     

Synthesis of distorted molecules based on spatial control with icosahedral carboranes

In the crystal structure of 1,2-bis(o-carboranyl)benzene (2), the benzene ring is remarkably twisted out of planarity, owing to the steric bulkiness of two adjacent carboranyl groups. In the carboracycle (3), the two benzene rings are slantingly stacked owing to spatial control by the carborane cages.