Novel platinum(IV)-carbohydrate complexes: Metal ion coordination behavior of monosaccharides in organic solvents

New platinum(IV)-coordinated carbohydrate complexes [PtMe3L]BF4 (14E-21E, 22D-24D) have been prepared from the reaction of [PtMe3(Me2CO)(3)]BF4 (1) with a wide range of isopropylidene-protected carbohydrates L'in acetone. These complexation reactions can be accompanied by a platinum-promoted cleavage of an isopropylidene group (14E, L' = 1,2;5,6-di-O-isopropylidene-alpha-D-glucofuranose (1A), L = 1,2-O-isopropylidene-alpha-D-glucofuranose; 15E, L' = 3-O-acetyl-1,2;5,6-di-O-isopropylidene-alpha-D-glucafuranose (2A), L = 3-O-acetyl-1,2-O-isopropylidenel-alpha-D-glucofuranose; 16E, L' = 3-O-(methylsulfonyl)-1,2;5;6-di-O-isopropylidene-alpha-D-glucofuranose (3A), L = 3-O-(methylsulfonyl)-1,2-O-isopropylidene-alpha-D-glucofuranose: 17E, L' = 1,2;5,6-di-O-isopropylidene-alpha-D-allofuranose (4A), L = 1,2-O-isopropylidene-alpha-D-allofuranose; 18E, L' = 2,3;4,6-di-O-isopropylidene-2-keto-L-gulonic acid(5A), L = 2,3-O-isopropylidene-2-keto-L-gulonic acid; 19E, L' = 2,3;4,6-di-O-isopropylidene-alpha-L-sorbofuranose (6A), L = 2,3-O-isopropylidene-alpha-L-sorbofuranose). In some cases, complexation proceeds without the loss of an isopropylidene group (14E, L = L' = 1,2-O-isopropylidene-alpha-D-glucofuranose (10B); 15E, L = L' = 3-O-acetyl-1,2-O-isopropylidene-alpha-D; glucofuranose (11B); 20E, L = L' = 1,2-O-isopropylidene-alpha-D-xylofuranose (12B), 21E, L = L' = 5,6-O-isopropylidene-D-gulono-gamma-lactone (13B)). Furthermore, complexes 22D-24D with diprotected carbohydrate ligands undergo a platinum-promoted cleavage of an isopropylidene group in wet methylene chloride to give 19E, cleavage of the carbohydrate ligand L (7A) to give [PtMe3(H2O)(3)]BF4, and substitution of the isopropylidene ligand by an aqua ligand to give [PtMe3L(H2O)]BF4 (24D', L = 2,3;4,5-di-O-isopropylidene beta-D-fructopyranose), respectively. Complex 14E reacted in acetone within 1 week in a platinum-promoted addition of an isopropylidene protecting group, yielding [PtM3L']BF4 (25D, L' = 1,2;5,6-di-O-isopropylidene-alpha-D-glucofuranose). The results show that carbohydrates can act as tridentate neutral ligands with a wide :variety-of donor sites: 3 x OH (14E, 17E-19E), 2 x OH + O-COMe (15E), 2 x OH + O-SO2Me (16E), 2 x OH + O-ring (20E), 2 x OH + O-acetal (21E), 1 x OH + O-ring + O-acetal (22D - 25D). Bidentate ligation (OH + O-ring) is observed in 24D'. Complexes E-14 singly C-13-labeled at each of the saccharide carbons were prepared, and an analysis of the J couplings involving the labeled carbons permitted an assignment of the solution conformation of the carbohydrate ligand. X-ray structure analysis of 19E (monoclinic, P2(1), a= 8.607(3) Angstrom, b = 9.955(4) Angstrom, c = 11.415(4) Angstrom, Z = 2) and 24D' (orthorhombic, P2(1)2(1)2(1), a = 9.851(2) Angstrom, b = 11.141(4) Angstrom, c = 20.418(6) Angstrom, Z = 4) exhibits the same coordination in the solid state as in solution, namely, via the three hydroxyl groups, yielding a strained-cyclic system (19E) and a five-membered 1,3,2-dioxaplatina ring (24D').