Synthesis and Crystallographic Studies of Disubstituted Carboranyl Alcohol Derivatives: Prevailing Chiral Recognition?

Abstract

The syntheses of new o-carboranyldiols bearing aromatic rings bis-[R(hydroxy)methyl]-1,2-dicarba-closo-dodecaborane (R = 2-pyridyl 1a, 3-pyridyl 1b, 4-pyridyl 1c, 2-quinolyl 1d, 4-quinolyl 1e, henyl 1f) are reported. The compounds are obtained as mixtures of meso (syn) and racemic (anti) stereoisomers with a slight diastereomeric excess (syn:anti ratio of 0.7:1) in all cases but in 1b. The cristal structures of the meso compounds syn-1a.2MeOH, syn-1b, syn-1f.0.25H2 O and racemic anti-1a.MeOH, anti-1a.EtOH, and anti-1d.2H2 O are reported. We provide an analysis of these compounds by means of NMR and X-ray crystallography, in the context of crystal engineering and chiral recognition. The results show that the cristal packings for these alcohols are dominated by the supramolecular O-H...N and/or O-H...O hydrogen bonds. Supramolecular analysis of all compounds in this work reveals that homochiral self-assembly, that is, formation of homochiral hydrogen bonded complexes, prevails over heterochiral self-assembly (formation of heterochiral hydrogen bonded complexes).