Dimolybdenum Method for Determination of the Absolute Configuration of vic-Diols - Foundations and Developments

A straightforward and versatile method for the determination of the absolute configuration of vic-diols is presented. The proposed method involves the in situ formation of chiral complexes of optically active vic-diols with the achiral dimolybdenum tetraacetate [Mo2(OAc)4] acting as an auxiliary chromophore. The resulting CD spectra are suitable for the assignment of absolute configuration, since the observed sign of Cotton effects arising within the d-d absorption bands of the metal cluster depends solely upon the chirality of the 1,2-diol ligands.An empirically based rule correlating a positive/negative helicity expressed by the O-C-C-O torsional angle with the sign of Cotton effects occurring in the 400-280 nm spectral range has been presented. The applicability of the rule is extended to sterically hindered sec/tert vic-diols.