Oxorhenium(V) Complexes of Carbohydrate Ligands

The reaction of anhydroerythritol (AnEryt) and methyl-β-D-galactopyranoside (Me-β-D-Galp) with dichloro[hydridotris(pyrazolyl)borato]oxorhenium(V) [(tpb)ReOCl2] in methanol/triethylamine results in the formation of blue crystals of the diolato complexes [(tpb)ReO(AnErytH−2)] (1) and [(tpb)ReO(Me-β-D-Galp3,4H−2)] (2). The amounts of anti-1 and syn-1 isomers are investigated by means of NMR spectroscopy and depend on the solvent chosen. For 2, the generally rigid pyranoside ligand enters the complex in a conformation that is even more heavily strained than the corresponding isopropylidene sugar in terms of torsion angles. Though anti and syn isomers are also formed in non-aqueous media initially, various synthetic procedures are given to obtain pure syn-2. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)