Palladium(II) complexes of the reducing sugars D-arabinose, D-ribose, rac-mannose, and D-galactose

The cellulose solvent Pd-en, an aqueous solution of [(en)Pd-11(OH)(2)] (en=ethylenediamine), reacts with the monosaccharides D-arabinose (D-Ara), D-ribose (D-Rib), rac-mannose (rac-Man), and D-galactose (D-Gal) under formation of dimetalated aldose complexes, if the molar ratio of Pd and sugar is 2:1 or larger. In the Pd-2 complexes, the aldoses are tetra-deprotonated and act as bisdiolato ligands. Two crystalline pentose complexes were isolated: [(en)(2)Pd-2(beta-D-Arap1,2,3,4 H-4)].5H(2)O (1) and [(en)(2)Pd-2(beta-D-Ribp1,2,3,4H(-4))].6.5H(2)O (2), along with two hexose complexes. With rac-Man, the major solution species is crystallized as the 9.4-hydrate [(en)(2)Pd-2(beta-rac-Manp-1,2,3,4H(-4))].9.4H(2)O (3). From the respective D-Gal solutions, [(en)(2)Pd-2(beta-D-Galf1,3,5,6H(-4))].5H(2)O.C2H5OH (4), with the sugar tetraanion in its furanose form, is crystallized though it is not the major species, rather the second most abundant in purely aqueous solutions. The Galf species is enriched in the mother liquors to the extent of 25% of total sugar content. Substitution of the en ligand by two molecules of ammonia, methylamine, or isopropylamine, respectively, results in the formation of different solution species. With the bulkiest ligand, isopropylamine, monometalation of the aldoses in the 1,2-position is exclusively observed.