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

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, phenyl 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 crystal structures of the meso compounds syn-1a·2MeOH, syn-1b, syn-1f·0.25H2O and racemic anti-1a·MeOH, anti-1a·EtOH, and anti-1d·2H2O 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 crystal 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).