CHROMATOGRAPHIC-SEPARATION OF STEREOISOMERS OF LIGAND-BRIDGED DIRUTHENIUM POLYPYRIDYL SPECIES

Cation-exchange chromatographic techniques have been developed to sepa rate stereoisomers of polymetallic complexes, using SP Sephadex C-25 a s support. Through the example of the ligand-bridged dinuclear cation u-bipym)](4+)(dmbpy=4,4'-dimethyl-2,2'-bipyridine, bipym=2,2'-bipyrimi dine), the isolation and characterisation of the, meso and rac diaster eoisomers by elution with aqueous sodium toluene-4-sulfonate solution are demonstrated. The effects of variation in salt concentration and t emperature on the efficacy of the separation are discussed. The enanti omeric pair of the rac diastereoisomer (Delta Delta and Lambda Lambda) was subsequently chromatographically resolved on SP Sephadex C-25, re lying upon the inherent chirality of the support. Optical resolutions using eluents with chiral anions [aquecus sodium (+)-O,O'-dibenzoyl-D- tartrate and sodium (-)-O,O'-dibenzoyl-L-tartrate] were investigated, with the (-)-enantiomer demonstrating a positive [the (+)-enantiomer a negative] synergistic effect in combination with the Sephadex support . Crystals of the meso form were isolated, allowing an X-ray structura l determination.