Über Hydroxygruppen an Platin(IV) koordinierte Kohlenhydrate - eine neue Klasse von Platinkomplexen mit bioaktiven Liganden

Carbohydrate–metallocene conjugates: selective formation of a zirconadioxacyclopentane-type dimer from the reaction of a bis(enolate)ZrCp2reagent with a glucofuranoside derivative

The zirconocene enolate complex bis(2-propenolato)ZrCp2 (1) reacts with two molar equivalents of the 1,2,3,4-O-tetramethyl-alpha-D-glucopyranoside (2) with liberation of two equivalents of acetone to yield cleanly the bis(carbohydrate)zirconcene complex (3). Alternatively 1 and the "bifunctional" glucose derivative 3-O-benzyl-1,2-O-isopropylidene-glucofuranoside (4) react to the corresponding zirconadioxacyclopentane-type metallacyclic product that was isolated as the respective dimer (5) featuring a sequence of linearly anellated five-, four-, five-membered metallacycles. Both carbohydrate zirconocene complexes 3 and 5 were characterized by NMR experiments as well as by X-ray diffraction.

Sugar ligands in organotitanium complexes

Using ligands derived from D-glucose, dinuclear organotitanium compounds with interesting structural features were synthesized.

Organometallic supramolecular chemistry with monosaccharides: triethylammonium mu-chloro-bis[chloro(eta5-cyclopentadienyl)-(methyl 4,6-o-benzylidene-beta-D-glucopyranosidato-1kappaO2,1:2kappaO3) zirconate]

The reaction of [CpZrCl3(thf)2] with methyl 4,6-O-benzylidene-beta-D-glucopyranoside (beta-MeBGH2, 1) in the presence of Et3N results in the formation of the zirconate complex [Et3NH] [(CpZrCl)2(mu-Cl) (mu-(beta-MeBG)]2] (2). X-ray structure analyses were performed from the ligand precursor beta-MeBGH2 1 as well as from 2. Compound 1 crystallizes in the monoclinic chiral space group P2(1). The molecules show a flat arrangement including the benzylidene protecting group, and are packed in columns. The columns are held together in pairs by the formation of hydrogen bonds between the hydroxy functions in positions 2 and 3. Compound 2 crystallizes in the orthorhombic space group P2(1)2(1)2(1). The beta-MeBG ligands are chelating the Zr atoms through the oxygen atoms in positions 2 and 3 of the glucopyranosidato ligand revealing a 1-zircona-2,5-dioxolane moiety each; the oxygen atom in position 3 is linked to both of the Zr atoms. Additionally one chloro ligand is bridging the two Zr centers. Two terminally bound chloro ligands stick out from the two Zr atoms into a chiral U-shaped cavity constructed by the two beta-MeBG ligands. The cavity incorporates the tertiary ammonium cation [Et3NH]+ which is bound to one of the terminal chloro ligands through a hydrogen bond. The inclusion of the [Et3NH]+ cation in the U-shaped cavity, even in solution, is demonstrated by NMR spectroscopic data.

13C-labeled platinum(IV)-carbohydrate complexes: structure determination based on (1)H-(1)H, (13)C-(1)H, and (13)C-(13)C spin-spin coupling constants

The reaction of D-mannose and D-allose with [PtMe(3)(Me(2)CO)(3)]BF(4) 1 in acetone affords complexes [PtMe(3)L]BF(4) 5 and 6 (5, L = alpha-D-mannofuranose; 6, L = beta-D-allofuranose). The coordination mode and conformation of the carbohydrate ligands in 5 and 6 in acetone-d(6) have been determined from an analysis of J(HH), J(CH), and J(CC) in complexes formed using site-specific (13)C-labeled D-mannose and D-allose. These coupling data are compared to those measured in (13)C-labeled complex [PtMe(3)L]BF(4) 2 (L = 1, 2-O-isopropylidene-alpha-D-glucofuranose) and 1, 2-O-isopropylidene-alpha-D-glucofuranose 3, whose solid-state structures are known, and in (13)C-labeled 1,2;5, 6-di-O-isopropylidene-alpha-D-glucofuranose 4. The preferred furanose ring conformations in 2 and 5 are very similar ((3)E/E(4) and E(4)/(o)E/E(1), respectively; eastern hemisphere of the pseudorotational itinerary), with platinum coordination involving O3, O5, and O6 of the saccharide. In contrast, the furanose ring of 6 prefers an (4)E/E(o)/(1)E geometry (western hemisphere of the pseudorotational itinerary) resulting from altered complexation involving O1, O5, and O6. Couplings within the exocyclic fragments of 2, 5, and 6 also support the existence of two different platinum coordination modes. In addition to establishing the structures and conformations of 2, 5, and 6 in solution, one-, two-, and three-bond J(CH) and J(CC) observed in these complexes provide new insights into the effect of structure and conformation on the magnitudes of these couplings in saccharides. Weak platinum(IV) complexation with the carbohydrate conformationally restricts the furanose and exocyclic fragment without introducing undesirable structural strain, thereby allowing more reliable correlations between structure and coupling magnitude.

The First Platinum(IV) Complexes with Glucopyranoside Ligands. A New Coordination Mode of Carbohydrates

[(PtMe(3)I)(4)] reacts with AgBF(4) in acetone to give fac-[PtMe(3)(Me(2)CO)(3)]BF(4) (2) which was isolated as strongly moisture and air sensitive, colorless crystals and characterized by microanalysis and NMR spectroscopy ((1)H, (13)C, (195)Pt). The X-ray structure analysis (orthorhombic, Pcab, a = 15.599(3) Å, b = 15.685(2) Å, c = 15.763(3) Å, Z = 8) reveals that 2 is monomeric and that the cation exhibits local C(3)(v)() symmetry. The reaction of 2 with glucopyranoses (1,6-anhydro-beta-D-glucopyranose (3a), 1-methyl-alpha-D-glucopyranoside (3b), and 1-phenyl-beta-D-glucopyranoside (3c)) yields carbohydrate complexes [PtMe(3)L]BF(4) (4a-4c, L = 3a-3c). The complexes were characterized by microanalysis, ESI mass spectrometry and by NMR spectroscopy ((1)H, (13)C, (195)Pt) displaying that the carbohydrates act as tridentate chelating ligands coordinated by the hydroxyl groups 2-OH and 4-OH and by the acetal oxygen atom of the pyranose ring. This structure was also confirmed by X-ray structure analysis of 4a (orthorhombic, P2(1)2(1)2(1), a = 6.404(1) Å, b = 8.636(2) Å, c = 27.161(5) Å, Z = 4). The cyclic system of the two five-membered and the one six-membered 1,3,2-dioxaplatina rings is not free from angle strain; two O-Pt-O angles are distinctly smaller than 90 degrees (O2-Pt-O5 73.6(2), O4-Pt-O5 75.6(2) degrees ). The Pt-O bond to the acetal oxygen atom in the pyranose ring is significantly longer (Pt-O5 2.288(5) Å) than the two Pt-OH bonds (Pt-O2 2.246(5), Pt-O4 2.248(4) and belongs to the longest Pt-O bonds at all.