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

The syntheses of new o-carboranyldiols bearing aromatic rings bis-[R(hydroxy)methy1]-1,2-dicarba-c/oso-dodecaborane (R = 2-pyridyl la, 3-pyridyl lb, 4pyridyl lc, 2-quinoly1 Id, 4-quinoly1 le, phenyl If) 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 lb. The crystal structures of the meso compounds syn-la.2Me0H, syn-lb, syn-If center dot 0.25H(2)O and racemic anti-la center dot MeOH, anti-la center dot EtOH, and anti-ld center dot 2H(2)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 crystal packings for these alcohols are dominated by the supramolecular OH center dot center dot N and/or O-H center dot center dot center dot 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).