Zum Heteroatomeinfluß in α- und β-funktionalisierten Alkylübergangsmetallkomplexen

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.