Palladium(II) Complexes of the Reducing Sugars D‐Arabinose, D‐Ribose, rac‐Mannose, and D‐Galactose

Abstract

The cellulose solvent Pd-en, an aqueous solution of [(en)Pd(II)(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))].5 H(2)O (1) and [(en)(2)Pd(2)(beta-D-Ribp1,2,3,4 H(-4))].6.5 H(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-Manp1,2,3,4 H(-4))].9.4 H(2)O (3). From the respective D-Gal solutions, [(en)(2)Pd(2)(beta-D-Galf1,3,5,6 H(-4))].5 H(2)O.C(2)H(5)OH (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.

Silicon Chelation in Aqueous and Nonaqueous Media: The Furanoidic Diol Approach

“…Attempts to crystallize the silicic acid ester of anhydroerythritol yielded a total of four polymorphic forms of Si-(AnErytH À2 ) 2 (6). When sorted according to the molecular structures, three polymorphs are formed from the spirocyclic molecules whose synthesis had been attempted.…”

“…Keywords: carbohydrates · NMR spectroscopy · Si ligands · silicates · spiro compounds tion, with the second containing a number of glycose-phenylsilicates in methanolic solution and includes some aldopentoses as well as two ketoses. [5][6][7] From the viewpoint of the carbohydrate, palladium is a "conservative" bonding partner as bonding to palladium alters the equilibrium mixture of aldose isomers in only a limited way-the prevalence of the pyranoses is maintained on deprotonation and bonding by the rather large metal center. [5,6] Silicon binding, on the other hand, induces a radical shift of the isomer mixture in the protic methanol solvent towards the furanose that bears its anomeric hydroxy group cis to the epimeric one.…”

“…[5][6][7] From the viewpoint of the carbohydrate, palladium is a "conservative" bonding partner as bonding to palladium alters the equilibrium mixture of aldose isomers in only a limited way-the prevalence of the pyranoses is maintained on deprotonation and bonding by the rather large metal center. [5,6] Silicon binding, on the other hand, induces a radical shift of the isomer mixture in the protic methanol solvent towards the furanose that bears its anomeric hydroxy group cis to the epimeric one. Thus, the most acidic cis-furanose group of a monosaccharide acts as a bidentate silicon chelator in the isolated bis-(diolato)(phenyl)silicates, as shown in the synthetic strategy that has been derived from studies on glycose model compounds.…”

“…Ph 2 Si(cisCptdH À2 ) (5) (Cptd = cyclopentanediol) is monomeric in solution but dimerizes on crystallization. Si(AnErytH À2 ) 2 (6) and Si(cis-CptdH À2 ) 2 (7) are monomeric spiro compounds in solution but are pentacoordinate dimers in the crystalline state. Pentacoordinate silicate ions are found in A[Si(OH)(AnErytH À2 (9) is a prototypical example as it shows the two most significant isomers in one crystal structure: the syn/anti and the anti/anti form (syn and anti define the oxolane ring orientation close to, or apart from, the monodentate ligand, respectively).…”

Monosaccharides as Silicon Chelators: Pentacoordinate Bis(diolato)(phenyl)silicates with the cis‐Furanose Isomers of Common Pentoses and Hexoses

“…For the remaining monosaccharides dealt with in this work, d-arabinose and d-ribose, structural data are available for palladium(ii) complexes of their pyranose forms. [6] Comparison of 2 and 3 with these latter structures illustrates the working hypothesis of this investigation. Both monosaccharides act as pyranose ligands with a larger bite towards the larger palladium(ii) and as furanose ligands with a flat chelate ring with the smaller silicon.…”